From 751f068486beb7cf8acfdae9a24f43ac4612a15a Mon Sep 17 00:00:00 2001
From: Toby Jaffey <toby@ringtailsoftware.co.uk>
Date: Mon, 8 Dec 2025 02:44:38 +0000
Subject: [PATCH] Rework host/target interface to use ecall and proper syscalls
 instead of CSRs

---
 README.md                     |   8 +-
 apps/crt0.s                   |  10 --
 apps/fib/Makefile             |   2 +-
 apps/hello-asm/Makefile       |   2 +-
 apps/hello-asm/hello-asm.s    |   9 --
 apps/helloworld/Makefile      |   2 +-
 apps/helloworld/helloworld.c  |  14 ++-
 apps/rust-hello/src/main.rs   |  29 +++---
 apps/sketch/Makefile          |   2 +-
 apps/zig-mandel/src/uvm.zig   |  42 +++-----
 apps/zigtris/src/uvm.zig      | 102 ++++++++-----------
 common/uvm32_common_custom.h  |   2 +-
 common/uvm32_target.h         |  34 ++++---
 common/uvm32_target_custom.h  |  17 ----
 host-arduino/host-arduino.ino |  41 ++++----
 host-arduino/uvm32.cpp        | 178 +++++++++++++++++++---------------
 host-arduino/uvm32.h          |   8 +-
 host-mini/host-mini.c         |  12 +--
 host-parallel/host-parallel.c |  12 +--
 host/host.c                   |  16 +--
 precompiled/fib.bin           | Bin 252 -> 476 bytes
 precompiled/helloworld.bin    | Bin 60 -> 48 bytes
 precompiled/mandel.bin        | Bin 204 -> 236 bytes
 precompiled/zigtris.bin       | Bin 16284 -> 16364 bytes
 uvm32/uvm32.c                 | 174 ++++++++++++++++++---------------
 uvm32/uvm32.h                 |   8 +-
 26 files changed, 360 insertions(+), 364 deletions(-)
 delete mode 100644 apps/crt0.s
 delete mode 100644 apps/hello-asm/hello-asm.s

diff --git a/README.md b/README.md
index a317b95..16a1b48 100644
--- a/README.md
+++ b/README.md
@@ -78,7 +78,7 @@ If the bytecode attempts to execute more instructions than the the passed value
 
 ## Internals
 
-uvm32 emulates a RISC-V 32bit CPU using [mini-rv32ima](https://github.com/cnlohr/mini-rv32ima). All IO from vm bytecode to the host is performed using [CSRs](https://five-embeddev.com/riscv-priv-isa-manual/Priv-v1.12/priv-csrs.html). Each "function" provided by the host requires a unique CSR value. A CSR passes a single `uint32_t` from bytecode to the host.
+uvm32 emulates a RISC-V 32bit CPU using [mini-rv32ima](https://github.com/cnlohr/mini-rv32ima). All IO from vm bytecode to the host is performed using `ecall` syscalls. Each "function" provided by the host requires a unique syscall value. A syscall passes a single `uint32_t` from bytecode to the host and may receive a returned `uint32_t`. The host may treat the value as a pointer and modify memory.
 
 uvm32 is always in one of 4 states, paused, running, ended or error.
 
@@ -102,7 +102,7 @@ There are two system ioreqs used by uvm32, `halt()` and `yield()`.
 `halt()` tells the host that the program has ended normally. `yield()` tells the host that the program requires more instructions to be executed.
 
 New ioreqs can be added to the host via `uvm32_init()`.
-Each ioreq maps a CSR number to a value understood by the host (`F_PRINTD` below) and has an associated type which tells the host how to interpret the data passed to the CSR.
+Each ioreq maps a syscall number to a value understood by the host (`F_PRINTD` below) and has an associated type which tells the host how to interpret the data passed to the syscall.
 
 Here is a full example of a working VM host from [apps/host-mini](apps/host-mini)
 
@@ -116,7 +116,7 @@ Here is a full example of a working VM host from [apps/host-mini](apps/host-mini
 #include "../common/uvm32_common_custom.h"
 
 // Precompiled binary program to print integers
-// This code expects to print via CSR 0x13C (IOREQ_PRINTD in common/uvm32_common_custom.h)
+// This code expects to print via syscall 0x13C (IOREQ_PRINTD in common/uvm32_common_custom.h)
 uint8_t rom[] = {
   0x23, 0x26, 0x11, 0x00, 0xef, 0x00, 0x00, 0x01, 0x73, 0x50, 0x80, 0x13,
   0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x93, 0x07, 0x00, 0x00,
@@ -131,7 +131,7 @@ typedef enum {
 
 // Map VM ioreq IOREQ_PRINTD (0x13C) to F_PRINTD, tell VM to expect write of a U32
 const uvm32_mapping_t env[] = {
-    { .csr = IOREQ_PRINTD, .typ = IOREQ_TYP_U32_WR, .code = F_PRINTD },
+    { .syscall = IOREQ_PRINTD, .typ = IOREQ_TYP_U32_WR, .code = F_PRINTD },
 };
 
 int main(int argc, char *argv[]) {
diff --git a/apps/crt0.s b/apps/crt0.s
deleted file mode 100644
index 3209b9d..0000000
--- a/apps/crt0.s
+++ /dev/null
@@ -1,10 +0,0 @@
-.section .initial_jump , "ax", %progbits
-.global _start
-.align 4
-_start:
-# sp is already setup by vm
-sw	ra,12(sp)
-jal	ra, main
-csrwi 0x138,0 # halt
-.section .data
-
diff --git a/apps/fib/Makefile b/apps/fib/Makefile
index 6e39a11..fed2e20 100644
--- a/apps/fib/Makefile
+++ b/apps/fib/Makefile
@@ -10,7 +10,7 @@ CFLAGS+=-g -Os -march=rv32ima_zicsr -mabi=ilp32 -static
 LDFLAGS:= -T ../linker.ld -nostdlib -Wl,--gc-sections
 LIBS:= #-lgcc # needed for softfp
 
-SRCS=${PROJECT}.c ../crt0.s
+SRCS=${PROJECT}.c ../crt0.S
 
 all:
 	${PREFIX}gcc -o ${PROJECT}.elf ${CFLAGS} ${LDFLAGS} ${SRCS} ${LIBS}
diff --git a/apps/hello-asm/Makefile b/apps/hello-asm/Makefile
index 5a0f92c..8b5e7ae 100644
--- a/apps/hello-asm/Makefile
+++ b/apps/hello-asm/Makefile
@@ -10,7 +10,7 @@ CFLAGS+=-g -Os -march=rv32ima_zicsr -mabi=ilp32 -static
 LDFLAGS:= -T ../linker.ld -nostdlib -Wl,--gc-sections
 LIBS:= #-lgcc # needed for softfp
 
-SRCS=hello-asm.s
+SRCS=hello-asm.S
 
 all:
 	${PREFIX}gcc -o ${PROJECT}.elf ${CFLAGS} ${LDFLAGS} ${SRCS} ${LIBS}
diff --git a/apps/hello-asm/hello-asm.s b/apps/hello-asm/hello-asm.s
deleted file mode 100644
index 3c1fabe..0000000
--- a/apps/hello-asm/hello-asm.s
+++ /dev/null
@@ -1,9 +0,0 @@
-.section .initial_jump , "ax", %progbits
-.global _start
-_start:
-la     a5, str
-csrrw zero,0x13b,a5 # println
-csrwi 0x138,0 # halt
-str:
-.ascii "Hi"
-
diff --git a/apps/helloworld/Makefile b/apps/helloworld/Makefile
index e508431..abff4b9 100644
--- a/apps/helloworld/Makefile
+++ b/apps/helloworld/Makefile
@@ -10,7 +10,7 @@ CFLAGS+=-g -Os -march=rv32ima_zicsr -mabi=ilp32 -static
 LDFLAGS:= -T ../linker.ld -nostdlib -Wl,--gc-sections
 LIBS:= #-lgcc # needed for softfp
 
-SRCS=${PROJECT}.c ../crt0.s
+SRCS=${PROJECT}.c ../crt0.S
 
 all:
 	${PREFIX}gcc -o ${PROJECT}.elf ${CFLAGS} ${LDFLAGS} ${SRCS} ${LIBS}
diff --git a/apps/helloworld/helloworld.c b/apps/helloworld/helloworld.c
index 975bddd..6d248a4 100644
--- a/apps/helloworld/helloworld.c
+++ b/apps/helloworld/helloworld.c
@@ -2,6 +2,18 @@
 #include "uvm32_target.h"
 
 void main(void) {
-    println("Hello world");
+    for (int i=0;i<10;i++) {
+        printd(i);
+    }
+#if 0
+    uint32_t c;
+    while(c = getc()) {
+        if (c != 0xFFFFFFFF) {
+            print("Got: ");
+            printx(c);
+            println("");
+        }
+    }
+#endif
 }
 
diff --git a/apps/rust-hello/src/main.rs b/apps/rust-hello/src/main.rs
index fc5c879..4d6281d 100644
--- a/apps/rust-hello/src/main.rs
+++ b/apps/rust-hello/src/main.rs
@@ -9,26 +9,27 @@ use core::panic::PanicInfo;
 include!(concat!(env!("OUT_DIR"), "/bindings.rs"));
 
 // startup code
-global_asm!(include_str!("../../crt0.s"));
+global_asm!(include_str!("../../crt0.S"));
 
-fn println(message: &str) {
+fn syscall(id: u32, n: u32) -> u32 {
+    let mut value;
     unsafe {
-        asm!(
-            "csrw {i}, {x}",
-            i = const IOREQ_PRINTLN,
-            x = in(reg) message.as_ptr(),
+        asm!("ecall",
+            in("a0") n,
+            in("a7") id,
+            lateout("a1") value,
         );
     }
+    return value;
+}
+
+fn println(message: &str) {
+    let addr_value = message.as_ptr() as u32;
+    syscall(IOREQ_PRINTLN, addr_value);
 }
 
 fn printd(n: u32) {
-    unsafe {
-        asm!(
-            "csrw {i}, {x}",
-            i = const IOREQ_PRINTD,
-            x = in(reg) n,
-        );
-    }
+    syscall(IOREQ_PRINTD, n);
 }
 
 #[no_mangle]
@@ -36,7 +37,7 @@ pub extern "C" fn main() {
     for i in 0..10 {
         printd(i);
     }
-    println("Hello, world!");
+    println("Hello, world!\0");
 }
 
 #[panic_handler]
diff --git a/apps/sketch/Makefile b/apps/sketch/Makefile
index ac77db1..524771d 100644
--- a/apps/sketch/Makefile
+++ b/apps/sketch/Makefile
@@ -10,7 +10,7 @@ CFLAGS+=-g -Os -march=rv32ima_zicsr -mabi=ilp32 -static
 LDFLAGS:= -T ../linker.ld -nostdlib -Wl,--gc-sections
 LIBS:= #-lgcc # needed for softfp
 
-SRCS=${PROJECT}.c ../crt0.s
+SRCS=${PROJECT}.c ../crt0.S
 
 all:
 	${PREFIX}gcc -o ${PROJECT}.elf ${CFLAGS} ${LDFLAGS} ${SRCS} ${LIBS}
diff --git a/apps/zig-mandel/src/uvm.zig b/apps/zig-mandel/src/uvm.zig
index e488c09..056da22 100644
--- a/apps/zig-mandel/src/uvm.zig
+++ b/apps/zig-mandel/src/uvm.zig
@@ -4,35 +4,25 @@ const uvm32 = @cImport({
 });
 const std = @import("std");
 
+pub inline fn syscall(id: u32, param: u32) u32 {
+    var val: u32 = undefined;
+    asm volatile ("ecall"
+        : [val] "={a1}" (val),
+        : [param] "{a0}" (param),
+          [id] "{a7}" (id),
+        : .{ .memory = true });
+    return val;
+}
+
 pub inline fn println(val: [:0]const u8) void {
-    asm volatile ("csrw " ++ std.fmt.comptimePrint("0x{x}", .{uvm32.IOREQ_PRINTLN}) ++ ", %[arg1]"
-        :
-        : [arg1] "r" (val.ptr),
-    );
-}
-
-pub inline fn printd(val: u32) void {
-    asm volatile ("csrw " ++ std.fmt.comptimePrint("0x{x}", .{uvm32.IOREQ_PRINTD}) ++ ", %[arg1]"
-        :
-        : [arg1] "r" (val),
-    );
-}
-
-pub inline fn printx(val: u32) void {
-    asm volatile ("csrw " ++ std.fmt.comptimePrint("0x{x}", .{uvm32.IOREQ_PRINTX}) ++ ", %[arg1]"
-        :
-        : [arg1] "r" (val),
-    );
-}
-
-pub inline fn printc(val: u32) void {
-    asm volatile ("csrw " ++ std.fmt.comptimePrint("0x{x}", .{uvm32.IOREQ_PRINTC}) ++ ", %[arg1]"
-        :
-        : [arg1] "r" (val),
-    );
+    _ = syscall(uvm32.IOREQ_PRINTLN, @intFromPtr(val.ptr));
 }
 
 pub inline fn yield() void {
-    asm volatile (std.fmt.comptimePrint("csrwi 0x{x}, 0", .{uvm32.IOREQ_YIELD}));
+    _ = syscall(uvm32.IOREQ_YIELD, 0);
+}
+
+pub inline fn printc(c:u8) void {
+    _ = syscall(uvm32.IOREQ_PRINTC, c);
 }
 
diff --git a/apps/zigtris/src/uvm.zig b/apps/zigtris/src/uvm.zig
index 631c481..5a66218 100644
--- a/apps/zigtris/src/uvm.zig
+++ b/apps/zigtris/src/uvm.zig
@@ -4,70 +4,52 @@ const uvm32 = @cImport({
 });
 const std = @import("std");
 
-// dupeZ would be better, but want to avoid using an allocator
-var new_buf:[128]u8 = undefined;
-pub inline fn print(m: []const u8) void {
-    @memcpy(new_buf[0..m.len], m);
-    new_buf[m.len] = 0;
-    const s = new_buf[0..m.len :0];
-
-    asm volatile ("csrw " ++ std.fmt.comptimePrint("0x{x}", .{uvm32.IOREQ_PRINT}) ++ ", %[arg1]"
-        :
-        : [arg1] "r" (s.ptr),
-    );
+pub inline fn syscall(id: u32, param: u32) u32 {
+    var val: u32 = undefined;
+    asm volatile ("ecall"
+        : [val] "={a1}" (val),
+        : [param] "{a0}" (param),
+          [id] "{a7}" (id),
+        : .{ .memory = true });
+    return val;
 }
 
-pub inline fn println(val: [:0]const u8) void {
-    asm volatile ("csrw " ++ std.fmt.comptimePrint("0x{x}", .{uvm32.IOREQ_PRINTLN}) ++ ", %[arg1]"
-        :
-        : [arg1] "r" (val.ptr),
-    );
-}
-
-pub inline fn printd(val: u32) void {
-    asm volatile ("csrw " ++ std.fmt.comptimePrint("0x{x}", .{uvm32.IOREQ_PRINTD}) ++ ", %[arg1]"
-        :
-        : [arg1] "r" (val),
-    );
-}
-
-pub inline fn printx(val: u32) void {
-    asm volatile ("csrw " ++ std.fmt.comptimePrint("0x{x}", .{uvm32.IOREQ_PRINTX}) ++ ", %[arg1]"
-        :
-        : [arg1] "r" (val),
-    );
-}
-
-pub inline fn printc(val: u32) void {
-    asm volatile ("csrw " ++ std.fmt.comptimePrint("0x{x}", .{uvm32.IOREQ_PRINTC}) ++ ", %[arg1]"
-        :
-        : [arg1] "r" (val),
-    );
-}
-
-pub inline fn yield() void {
-    asm volatile (std.fmt.comptimePrint("csrwi 0x{x}, 0", .{uvm32.IOREQ_YIELD}));
-}
-
-var millis_storage:u32 = 0;
-pub inline fn millis() u32 {
-    asm volatile ("csrw " ++ std.fmt.comptimePrint("0x{x}", .{uvm32.IOREQ_MILLIS}) ++ ", %[arg1]"
-        :
-        : [arg1] "r" (&millis_storage),
-    );
-    return millis_storage;
-}
-
-var getch_storage:u32 = 0;
 pub inline fn getch() ?u8 {
-    asm volatile ("csrw " ++ std.fmt.comptimePrint("0x{x}", .{uvm32.IOREQ_GETC}) ++ ", %[arg1]"
-        :
-        : [arg1] "r" (&getch_storage),
-    );
-    if (getch_storage <= 0xFF) {
-        return @truncate(getch_storage);
-    } else {
+    const key = syscall(uvm32.IOREQ_GETC, 0);
+    if (key == 0xFFFFFFFF) {
         return null;
+    } else {
+        return @truncate(key);
     }
 }
 
+pub inline fn millis() u32 {
+    return syscall(uvm32.IOREQ_MILLIS, 0);
+}
+
+// dupeZ would be better, but want to avoid using an allocator
+// this is of course, unsafe...
+var termination_buf:[128]u8 = undefined;
+
+pub inline fn print(m: []const u8) void {
+    @memcpy(termination_buf[0..m.len], m);
+    termination_buf[m.len] = 0;
+    const s = termination_buf[0..m.len :0];
+    _ = syscall(uvm32.IOREQ_PRINT, @intFromPtr(s.ptr));
+}
+
+pub inline fn println(m: []const u8) void {
+    @memcpy(termination_buf[0..m.len], m);
+    termination_buf[m.len] = 0;
+    const s = termination_buf[0..m.len :0];
+    _ = syscall(uvm32.IOREQ_PRINTLN, @intFromPtr(s.ptr));
+}
+
+pub inline fn yield() void {
+    _ = syscall(uvm32.IOREQ_YIELD, 0);
+}
+
+pub inline fn printc(c:u8) void {
+    _ = syscall(uvm32.IOREQ_PRINTC, c);
+}
+
diff --git a/common/uvm32_common_custom.h b/common/uvm32_common_custom.h
index 7f6d0a8..1131458 100644
--- a/common/uvm32_common_custom.h
+++ b/common/uvm32_common_custom.h
@@ -1,6 +1,6 @@
 // Definitions needed by both host and target
 
-// CSRs for exposed host functions
+// syscalls for exposed host functions
 #define IOREQ_PRINT 0x13A
 #define IOREQ_PRINTLN 0x13B
 #define IOREQ_PRINTD 0x13C
diff --git a/common/uvm32_target.h b/common/uvm32_target.h
index 2a9edf2..b4afdb3 100644
--- a/common/uvm32_target.h
+++ b/common/uvm32_target.h
@@ -9,17 +9,29 @@ typedef int bool;
 #define true 1
 #define false 0
 
-// Convenience macro for defining CSR helper functions
-#define xstr(a) str(a)
-#define str(a) #a
-#define DEFINE_CSR_WRITE_FUNCTION(function_name, csr, typ) \
-    static void function_name(typ val) { \
-	    asm volatile( ".option norvc\ncsrrw x0," xstr(csr) ", %0\n" : : "r" (val)); \
-    }
-#define DEFINE_CSR_WRITE_FUNCTION_VOID(function_name, csr) \
-    static void function_name(void) { \
-	    asm volatile( ".option norvc\ncsrwi " xstr(csr) ", 0"); \
-    }
+static uint32_t syscall(uint32_t id, uint32_t param) {
+    register uint32_t a0 asm("a0") = (uint32_t)(param);
+    register uint32_t a1 asm("a1");
+    register uint32_t a7 asm("a7") = (uint32_t)(id);
+
+    asm volatile (
+        "ecall"
+        : "=r"(a1) // output
+        : "r"(a0), "r"(a7) // input
+        : "memory"
+    );
+    return a1;
+}
+
+#define syscall_cast(id, x) syscall((uint32_t)id, (uint32_t)x)
+#define println(x) syscall_cast(IOREQ_PRINTLN, x)
+#define print(x) syscall_cast(IOREQ_PRINT, x)
+#define printd(x) syscall_cast(IOREQ_PRINTD, x)
+#define printx(x) syscall_cast(IOREQ_PRINTX, x)
+#define millis() syscall_cast(IOREQ_MILLIS, 0)
+#define printc() syscall_cast(IOREQ_PRINTC, 0)
+#define getc() syscall_cast(IOREQ_GETC, 0)
+#define yield() syscall_cast(IOREQ_YIELD, 0)
 
 #include "uvm32_common_custom.h"
 #include "uvm32_target_custom.h"
diff --git a/common/uvm32_target_custom.h b/common/uvm32_target_custom.h
index 8aa3e12..e69de29 100644
--- a/common/uvm32_target_custom.h
+++ b/common/uvm32_target_custom.h
@@ -1,17 +0,0 @@
-// Define wrapper functions for target code to call CSRs
-
-DEFINE_CSR_WRITE_FUNCTION(print, IOREQ_PRINT, const char *)
-DEFINE_CSR_WRITE_FUNCTION(printd, IOREQ_PRINTD, uint32_t)
-DEFINE_CSR_WRITE_FUNCTION(printx, IOREQ_PRINTX, uint32_t)
-DEFINE_CSR_WRITE_FUNCTION(printc, IOREQ_PRINTC, char)
-DEFINE_CSR_WRITE_FUNCTION(println, IOREQ_PRINTLN, const char *)
-DEFINE_CSR_WRITE_FUNCTION_VOID(halt, IOREQ_HALT)
-DEFINE_CSR_WRITE_FUNCTION_VOID(yield, IOREQ_YIELD)
-DEFINE_CSR_WRITE_FUNCTION(millis_internal, IOREQ_MILLIS, uint32_t *)
-
-static inline uint32_t millis(void) {
-    static uint32_t m;
-    millis_internal(&m);
-    return m;
-}
-
diff --git a/host-arduino/host-arduino.ino b/host-arduino/host-arduino.ino
index 269b443..fb0d14c 100644
--- a/host-arduino/host-arduino.ino
+++ b/host-arduino/host-arduino.ino
@@ -3,25 +3,28 @@
 #include "common/uvm32_common_custom.h"
 
 // Precompiled binary program to print integers
-// This code expects to print via CSR 0x13C (IOREQ_PRINTD in common/uvm32_common_custom.h)
+// This code expects to print via syscall 0x13C (IOREQ_PRINTD in common/uvm32_common_custom.h)
 uint8_t rom[] = {
-    0x23, 0x26, 0x11, 0x00, 0xef, 0x00, 0x80, 0x00, 0x73, 0x50, 0x80, 0x13,
-    0x37, 0xf6, 0xff, 0xff, 0xb7, 0x17, 0x00, 0x00, 0x37, 0xe7, 0xff, 0xff,
-    0x13, 0x05, 0xf0, 0x01, 0xb7, 0x45, 0x00, 0x00, 0x13, 0x06, 0xd6, 0xcc,
-    0x93, 0x86, 0x37, 0x33, 0x13, 0x07, 0x77, 0xe6, 0x93, 0x87, 0x37, 0xb3,
-    0x13, 0x08, 0xa0, 0x00, 0x63, 0xcc, 0xc6, 0x06, 0x93, 0x08, 0x07, 0x00,
-    0x63, 0xc2, 0xe7, 0x06, 0x93, 0x03, 0x00, 0x00, 0x13, 0x03, 0x00, 0x00,
-    0x13, 0x0e, 0x00, 0x00, 0x93, 0x0e, 0x00, 0x00, 0x93, 0x02, 0x00, 0x02,
-    0x13, 0x8f, 0x02, 0xfe, 0x63, 0x6e, 0xe5, 0x03, 0x33, 0x0f, 0x73, 0x00,
-    0x63, 0xea, 0xe5, 0x03, 0x33, 0x8e, 0xce, 0x03, 0xb3, 0x0e, 0x73, 0x40,
-    0x73, 0x50, 0x90, 0x13, 0x13, 0x5e, 0xbe, 0x40, 0xb3, 0x8e, 0x1e, 0x01,
-    0x33, 0x0e, 0xce, 0x00, 0x33, 0x83, 0xde, 0x03, 0x13, 0x53, 0xc3, 0x00,
-    0xb3, 0x03, 0xce, 0x03, 0x93, 0xd3, 0xc3, 0x00, 0x93, 0x82, 0x12, 0x00,
-    0x6f, 0xf0, 0x5f, 0xfc, 0x73, 0x90, 0x02, 0x14, 0x93, 0x88, 0x18, 0x09,
-    0xe3, 0xd2, 0x17, 0xfb, 0x73, 0x10, 0x08, 0x14, 0x13, 0x06, 0x96, 0x19,
-    0xe3, 0xd8, 0xc6, 0xf8, 0x37, 0x05, 0x00, 0x80, 0x13, 0x05, 0x05, 0x0c,
-    0x73, 0x10, 0xb5, 0x13, 0x67, 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
-    0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64, 0x00
+  0x23, 0x26, 0x11, 0x00, 0xef, 0x00, 0xc0, 0x00, 0x93, 0x08, 0x80, 0x13,
+  0x73, 0x00, 0x00, 0x00, 0x37, 0xf5, 0xff, 0xff, 0xb7, 0x15, 0x00, 0x00,
+  0x37, 0xe6, 0xff, 0xff, 0x93, 0x06, 0xf0, 0x01, 0x13, 0x07, 0xd5, 0xcc,
+  0x93, 0x87, 0x35, 0x33, 0x13, 0x08, 0x76, 0xe6, 0x93, 0x82, 0x35, 0xb3,
+  0x37, 0x43, 0x00, 0x00, 0x63, 0xc8, 0xe7, 0x08, 0x93, 0x03, 0x08, 0x00,
+  0x63, 0xca, 0x02, 0x07, 0x93, 0x08, 0x00, 0x00, 0x93, 0x05, 0x00, 0x00,
+  0x13, 0x0e, 0x00, 0x00, 0x93, 0x0e, 0x00, 0x00, 0x13, 0x06, 0x00, 0x02,
+  0x13, 0x05, 0x06, 0xfe, 0x63, 0xe2, 0xa6, 0x04, 0x33, 0x85, 0x15, 0x01,
+  0x63, 0x6e, 0xa3, 0x02, 0x13, 0x05, 0x00, 0x00, 0x33, 0x8e, 0xce, 0x03,
+  0xb3, 0x8e, 0x15, 0x41, 0x93, 0x08, 0x90, 0x13, 0x73, 0x00, 0x00, 0x00,
+  0x13, 0x5e, 0xbe, 0x40, 0xb3, 0x8e, 0x7e, 0x00, 0x33, 0x0e, 0xee, 0x00,
+  0xb3, 0x85, 0xde, 0x03, 0x93, 0xd5, 0xc5, 0x00, 0x33, 0x05, 0xce, 0x03,
+  0x93, 0x58, 0xc5, 0x00, 0x13, 0x06, 0x16, 0x00, 0x6f, 0xf0, 0xdf, 0xfb,
+  0x93, 0x08, 0x00, 0x14, 0x13, 0x05, 0x06, 0x00, 0x73, 0x00, 0x00, 0x00,
+  0x93, 0x83, 0x13, 0x09, 0xe3, 0xda, 0x72, 0xf8, 0x13, 0x05, 0xa0, 0x00,
+  0x93, 0x08, 0x00, 0x14, 0x73, 0x00, 0x00, 0x00, 0x13, 0x07, 0x97, 0x19,
+  0xe3, 0xdc, 0xe7, 0xf6, 0x37, 0x05, 0x00, 0x80, 0x13, 0x05, 0x05, 0x0e,
+  0x93, 0x08, 0xb0, 0x13, 0x73, 0x00, 0x00, 0x00, 0x67, 0x80, 0x00, 0x00,
+  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x48, 0x65, 0x6c, 0x6c,
+  0x6f, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64, 0x00
 };
 
 // Create an identifier for our host handler
@@ -98,5 +101,5 @@ void loop(void) {
         delay(2000);
     }
 
-    return 0;
+    return;
 }
diff --git a/host-arduino/uvm32.cpp b/host-arduino/uvm32.cpp
index 69da7c4..4851a58 100644
--- a/host-arduino/uvm32.cpp
+++ b/host-arduino/uvm32.cpp
@@ -24,7 +24,7 @@ static void setup_err_evt(uvm32_state_t *vmst, uvm32_evt_t *evt) {
 
 static void setStatus(uvm32_state_t *vmst, uvm32_status_t newStatus) {
     if (vmst->status == UVM32_STATUS_ERROR) {
-        // always stay in error state until a uvm32_reset()
+        // always stay in error state until a uvm32_init()
         return;
     } else {
         vmst->status = newStatus;
@@ -47,7 +47,7 @@ void uvm32_init(uvm32_state_t *vmst, const uvm32_mapping_t *mappings, uint32_t n
     // setup stack pointer
     // la	sp, _sstack
     // addi	sp,sp,-16
-    vmst->core->regs[2] = (MINIRV32_RAM_IMAGE_OFFSET + UVM32_MEMORY_SIZE) - 16;
+    vmst->core->regs[2] = (MINIRV32_RAM_IMAGE_OFFSET + UVM32_MEMORY_SIZE - sizeof(struct MiniRV32IMAState)) - 16;
     vmst->core->regs[10] = 0x00;  //hart ID
     vmst->core->regs[11] = 0;
     vmst->core->extraflags |= 3;  // Machine-mode.
@@ -67,8 +67,45 @@ bool uvm32_load(uvm32_state_t *vmst, uint8_t *rom, int len) {
     return true;
 }
 
+// Read C-string up to terminator and return len,ptr
+static void get_safeptr_terminated(uvm32_state_t *vmst, uint32_t addr, uint8_t terminator, uvm32_evt_ioreq_buf_t *buf) {
+    uint32_t ptrstart = addr - MINIRV32_RAM_IMAGE_OFFSET;
+    uint32_t p = ptrstart;
+    if (p >= UVM32_MEMORY_SIZE) {
+        setStatusErr(vmst, UVM32_ERR_MEM_RD);
+        buf->ptr = NULL;
+        buf->len = 0;
+        return;
+    }
+    while(vmst->memory[p] != terminator) {
+        p++;
+        if (p >= UVM32_MEMORY_SIZE) {
+            setStatusErr(vmst, UVM32_ERR_MEM_RD);
+            buf->ptr = NULL;
+            buf->len = 0;
+            return;
+        }
+    }
+    buf->ptr = &vmst->memory[ptrstart];
+    buf->len = p - ptrstart;
+}
+
+#if 0
+static void get_safeptr(uvm32_state_t *vmst, uint32_t addr, uint32_t len, uvm32_evt_ioreq_buf_t *buf) {
+    uint32_t ptrstart = addr - MINIRV32_RAM_IMAGE_OFFSET;
+    if (ptrstart + len >= UVM32_MEMORY_SIZE) {
+        setStatusErr(vmst, UVM32_ERR_MEM_RD);
+    }
+    buf->ptr = &vmst->memory[ptrstart];
+    buf->len = len;
+}
+#endif
+
+
 uint32_t uvm32_run(uvm32_state_t *vmst, uvm32_evt_t *evt, uint32_t instr_meter) {
     uint32_t num_instr = 0;
+//    uvm32_evt_ioreq_buf_t b;
+
     if (vmst->status != UVM32_STATUS_PAUSED) {
         setStatusErr(vmst, UVM32_ERR_NOTREADY);
         setup_err_evt(vmst, evt);
@@ -80,7 +117,65 @@ uint32_t uvm32_run(uvm32_state_t *vmst, uvm32_evt_t *evt, uint32_t instr_meter)
     // run CPU until no longer in running state
     while(vmst->status == UVM32_STATUS_RUNNING) {
         uint64_t elapsedUs = 1;
-        if (0 != MiniRV32IMAStep(vmst, vmst->core, vmst->memory, 0, elapsedUs, 1)) {
+        uint32_t ret;
+        ret = MiniRV32IMAStep(vmst, vmst->core, vmst->memory, 0, elapsedUs, 1);
+        if (3 == ret) {
+            const uint32_t syscall = vmst->core->regs[17];  // a7
+            uint32_t value = vmst->core->regs[10]; // a0
+            bool syscall_valid = false;
+            // on exception we should jump to mtvec, but we handle directly
+            // and skip over the ecall instruction
+            vmst->core->pc += 4;
+            switch(syscall) {
+                // inbuilt syscalls
+                 case IOREQ_HALT:
+                    setStatus(vmst, UVM32_STATUS_ENDED);
+                    syscall_valid = true;
+                break;
+                case IOREQ_YIELD:
+                    vmst->ioevt.typ = UVM32_EVT_YIELD;
+                    setStatus(vmst, UVM32_STATUS_PAUSED);
+                    syscall_valid = true;
+                break;
+
+                // user defined syscalls
+                default:
+                    // search in mappings
+                    for (int i=0;i<vmst->numMappings;i++) {
+                        if (syscall == vmst->mappings[i].syscall) {
+                            // setup ioevt.data according to mapping typ
+                            switch(vmst->mappings[i].typ) {
+                                case IOREQ_TYP_VOID:
+                                break;
+                                case IOREQ_TYP_U32_WR:
+                                    vmst->ioevt.data.ioreq.val.u32 = value;
+                                break;
+                                case IOREQ_TYP_BUF_TERMINATED_WR:
+                                    get_safeptr_terminated(vmst, value, 0x00, &vmst->ioevt.data.ioreq.val.buf);
+                                break;
+                                case IOREQ_TYP_U32_RD:
+//                                    get_safeptr(vmst, value, 4, &b);
+                                    vmst->ioevt.data.ioreq.val.u32p = &vmst->core->regs[11]; // r1, //(uint32_t *)b.ptr;
+                                break;
+                            }
+                            vmst->ioevt.typ = UVM32_EVT_IOREQ;
+                            vmst->ioevt.data.ioreq.code = vmst->mappings[i].code;
+                            vmst->ioevt.data.ioreq.typ = vmst->mappings[i].typ;
+//#warning FIXME, retval
+//                            vmst->core->regs[11] = 456; // r1
+                            setStatus(vmst, UVM32_STATUS_PAUSED);
+                            syscall_valid = true;
+                            break;  // stop searching
+                        }
+                    }
+                    // no mapping found
+                    if (!syscall_valid) {
+                        setStatusErr(vmst, UVM32_ERR_BAD_SYSCALL);
+                    }
+                break;
+            }
+        } else if (ret != 0) {
+            // unhandled exception
             setStatusErr(vmst, UVM32_ERR_INTERNAL_CORE);
             setup_err_evt(vmst, evt);
         }
@@ -116,83 +211,6 @@ uint32_t uvm32_run(uvm32_state_t *vmst, uvm32_evt_t *evt, uint32_t instr_meter)
     }
 }
 
-// Read C-string up to terminator and return len,ptr
-static void get_safeptr_terminated(uvm32_state_t *vmst, uint32_t addr, uint8_t terminator, uvm32_evt_ioreq_buf_t *buf) {
-    uint32_t ptrstart = addr - MINIRV32_RAM_IMAGE_OFFSET;
-    uint32_t p = ptrstart;
-    if (p >= UVM32_MEMORY_SIZE) {
-        setStatusErr(vmst, UVM32_ERR_MEM_RD);
-        buf->ptr = NULL;
-        buf->len = 0;
-        return;
-    }
-    while(vmst->memory[p] != terminator) {
-        p++;
-        if (p >= UVM32_MEMORY_SIZE) {
-            setStatusErr(vmst, UVM32_ERR_MEM_RD);
-            buf->ptr = NULL;
-            buf->len = 0;
-            return;
-        }
-    }
-    buf->ptr = &vmst->memory[ptrstart];
-    buf->len = p - ptrstart;
-}
-
-static void get_safeptr(uvm32_state_t *vmst, uint32_t addr, uint32_t len, uvm32_evt_ioreq_buf_t *buf) {
-    uint32_t ptrstart = addr - MINIRV32_RAM_IMAGE_OFFSET;
-    if (ptrstart + len >= UVM32_MEMORY_SIZE) {
-        setStatusErr(vmst, UVM32_ERR_MEM_RD);
-    }
-    buf->ptr = &vmst->memory[ptrstart];
-    buf->len = len;
-}
-
-void uvm32_HandleOtherCSRWrite(void *userdata, uint16_t csrno, uint32_t value) {
-    uvm32_evt_ioreq_buf_t b;
-    uvm32_state_t *vmst = (uvm32_state_t *)userdata;
-
-    switch(csrno) {
-        case IOREQ_HALT:
-            setStatus(vmst, UVM32_STATUS_ENDED);
-        break;
-        case IOREQ_YIELD:
-            vmst->ioevt.typ = UVM32_EVT_YIELD;
-            setStatus(vmst, UVM32_STATUS_PAUSED);
-        break;
-
-        default:
-            // search in mappings
-            for (int i=0;i<vmst->numMappings;i++) {
-                if (csrno == vmst->mappings[i].csr) {
-                    // setup ioevt.data according to mapping typ
-                    switch(vmst->mappings[i].typ) {
-                        case IOREQ_TYP_VOID:
-                        break;
-                        case IOREQ_TYP_U32_WR:
-                            vmst->ioevt.data.ioreq.val.u32 = value;
-                        break;
-                        case IOREQ_TYP_BUF_TERMINATED_WR:
-                            get_safeptr_terminated(vmst, value, 0x00, &vmst->ioevt.data.ioreq.val.buf);
-                        break;
-                        case IOREQ_TYP_U32_RD:
-                            get_safeptr(vmst, value, 4, &b);
-                            vmst->ioevt.data.ioreq.val.u32p = (uint32_t *)b.ptr;
-                        break;
-                    }
-                    vmst->ioevt.typ = UVM32_EVT_IOREQ;
-                    vmst->ioevt.data.ioreq.code = vmst->mappings[i].code;
-                    vmst->ioevt.data.ioreq.typ = vmst->mappings[i].typ;
-                    setStatus(vmst, UVM32_STATUS_PAUSED);
-                    return;
-                }
-           }
-           // no mapping found
-           setStatusErr(vmst, UVM32_ERR_BAD_CSR);
-        break;
-    }
-}
-
 bool uvm32_hasEnded(const uvm32_state_t *vmst) {
     return vmst->status == UVM32_STATUS_ENDED;
 }
diff --git a/host-arduino/uvm32.h b/host-arduino/uvm32.h
index 4caaa7b..9a55b76 100644
--- a/host-arduino/uvm32.h
+++ b/host-arduino/uvm32.h
@@ -13,7 +13,7 @@
     X(UVM32_ERR_NOTREADY) \
     X(UVM32_ERR_MEM_RD) \
     X(UVM32_ERR_MEM_WR) \
-    X(UVM32_ERR_BAD_CSR) \
+    X(UVM32_ERR_BAD_SYSCALL) \
     X(UVM32_ERR_HUNG) \
     X(UVM32_ERR_INTERNAL_CORE) \
     X(UVM32_ERR_INTERNAL_STATE) \
@@ -40,9 +40,9 @@ typedef enum {
 
 typedef uint32_t uvm32_user_ioreq_code_t;
 
-// user supplied mapping from csr to typed ioreq
+// user supplied mapping from syscall to typed ioreq
 typedef struct {
-    uint32_t csr;
+    uint32_t syscall;
     uvm32_user_ioreq_code_t code;
     uvm32_ioreq_typ_t typ;
 } uvm32_mapping_t;
@@ -75,11 +75,9 @@ typedef struct {
     } data;
 } uvm32_evt_t;
 
-void uvm32_HandleOtherCSRWrite(void *userdata, uint16_t csrno, uint32_t value);
 #define MINIRV32_DECORATE static
 #define MINI_RV32_RAM_SIZE UVM32_MEMORY_SIZE
 #define MINIRV32_POSTEXEC(pc, ir, retval) {if (retval > 0) return 3;}
-#define MINIRV32_OTHERCSR_WRITE(csrno, value) uvm32_HandleOtherCSRWrite(userdata, csrno, value);
 #ifndef MINIRV32_IMPLEMENTATION
 #define MINIRV32_STEPPROTO
 #endif
diff --git a/host-mini/host-mini.c b/host-mini/host-mini.c
index dce277a..fe1e76a 100644
--- a/host-mini/host-mini.c
+++ b/host-mini/host-mini.c
@@ -5,12 +5,12 @@
 #include "../common/uvm32_common_custom.h"
 
 // Precompiled binary program to print integers
-// This code expects to print via CSR 0x13C (IOREQ_PRINTD in common/uvm32_common_custom.h)
+// This code expects to print via syscall 0x13C (IOREQ_PRINTD in common/uvm32_common_custom.h)
 uint8_t rom[] = {
-  0x23, 0x26, 0x11, 0x00, 0xef, 0x00, 0x00, 0x01, 0x73, 0x50, 0x80, 0x13,
-  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x93, 0x07, 0x00, 0x00,
-  0x13, 0x07, 0xa0, 0x00, 0x73, 0x90, 0xc7, 0x13, 0x93, 0x87, 0x17, 0x00,
-  0xe3, 0x9c, 0xe7, 0xfe, 0x67, 0x80, 0x00, 0x00
+    0x23, 0x26, 0x11, 0x00, 0xef, 0x00, 0x00, 0x01, 0x93, 0x08, 0x80, 0x13,
+    0x73, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x13, 0x05, 0x00, 0x00,
+    0x93, 0x07, 0xa0, 0x00, 0x93, 0x08, 0xc0, 0x13, 0x73, 0x00, 0x00, 0x00,
+    0x13, 0x05, 0x15, 0x00, 0xe3, 0x1a, 0xf5, 0xfe, 0x67, 0x80, 0x00, 0x00
 };
 
 // Create an identifier for our host handler
@@ -20,7 +20,7 @@ typedef enum {
 
 // Map VM ioreq IOREQ_PRINTD (0x13C) to F_PRINTD, tell VM to expect write of a U32
 const uvm32_mapping_t env[] = {
-    { .csr = IOREQ_PRINTD, .typ = IOREQ_TYP_U32_WR, .code = F_PRINTD },
+    { .syscall = IOREQ_PRINTD, .typ = IOREQ_TYP_U32_WR, .code = F_PRINTD },
 };
 
 int main(int argc, char *argv[]) {
diff --git a/host-parallel/host-parallel.c b/host-parallel/host-parallel.c
index 699258d..f9f09e0 100644
--- a/host-parallel/host-parallel.c
+++ b/host-parallel/host-parallel.c
@@ -13,12 +13,12 @@
 #define SCHEDULE_RANDOM()       scheduler_index = rand()%NUM_VM
 
 // Precompiled binary program to print integers
-// This code expects to print via CSR 0x13C (IOREQ_PRINTD in common/uvm32_common_custom.h)
+// This code expects to print via syscall 0x13C (IOREQ_PRINTD in common/uvm32_common_custom.h)
 uint8_t rom[] = {
-  0x23, 0x26, 0x11, 0x00, 0xef, 0x00, 0x00, 0x01, 0x73, 0x50, 0x80, 0x13,
-  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x93, 0x07, 0x00, 0x00,
-  0x13, 0x07, 0xa0, 0x00, 0x73, 0x90, 0xc7, 0x13, 0x93, 0x87, 0x17, 0x00,
-  0xe3, 0x9c, 0xe7, 0xfe, 0x67, 0x80, 0x00, 0x00
+    0x23, 0x26, 0x11, 0x00, 0xef, 0x00, 0x00, 0x01, 0x93, 0x08, 0x80, 0x13,
+    0x73, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x13, 0x05, 0x00, 0x00,
+    0x93, 0x07, 0xa0, 0x00, 0x93, 0x08, 0xc0, 0x13, 0x73, 0x00, 0x00, 0x00,
+    0x13, 0x05, 0x15, 0x00, 0xe3, 0x1a, 0xf5, 0xfe, 0x67, 0x80, 0x00, 0x00
 };
 
 // Create an identifier for our host handler
@@ -28,7 +28,7 @@ typedef enum {
 
 // Map VM ioreq IOREQ_PRINTD to F_PRINTD, tell VM to expect write of a U32
 const uvm32_mapping_t env[] = {
-    { .csr = IOREQ_PRINTD, .typ = IOREQ_TYP_U32_WR, .code = F_PRINTD },
+    { .syscall = IOREQ_PRINTD, .typ = IOREQ_TYP_U32_WR, .code = F_PRINTD },
 };
 
 int main(int argc, char *argv[]) {
diff --git a/host/host.c b/host/host.c
index 41b122f..d5876a7 100644
--- a/host/host.c
+++ b/host/host.c
@@ -22,15 +22,15 @@ typedef enum {
     F_GETC,
 } f_code_t;
 
-// Map exposed ioreqs to CSRs
+// Map exposed ioreqs to syscalls
 const uvm32_mapping_t env[] = {
-    { .csr = IOREQ_PRINTLN, .typ = IOREQ_TYP_BUF_TERMINATED_WR, .code = F_PRINTLN },
-    { .csr = IOREQ_PRINT, .typ = IOREQ_TYP_BUF_TERMINATED_WR, .code = F_PRINT },
-    { .csr = IOREQ_PRINTD, .typ = IOREQ_TYP_U32_WR, .code = F_PRINTD },
-    { .csr = IOREQ_PRINTX, .typ = IOREQ_TYP_U32_WR, .code = F_PRINTX },
-    { .csr = IOREQ_PRINTC, .typ = IOREQ_TYP_U32_WR, .code = F_PRINTC },
-    { .csr = IOREQ_MILLIS, .typ = IOREQ_TYP_U32_RD, .code = F_MILLIS },
-    { .csr = IOREQ_GETC, .typ = IOREQ_TYP_U32_RD, .code = F_GETC },
+    { .syscall = IOREQ_PRINTLN, .typ = IOREQ_TYP_BUF_TERMINATED_WR, .code = F_PRINTLN },
+    { .syscall = IOREQ_PRINT, .typ = IOREQ_TYP_BUF_TERMINATED_WR, .code = F_PRINT },
+    { .syscall = IOREQ_PRINTD, .typ = IOREQ_TYP_U32_WR, .code = F_PRINTD },
+    { .syscall = IOREQ_PRINTX, .typ = IOREQ_TYP_U32_WR, .code = F_PRINTX },
+    { .syscall = IOREQ_PRINTC, .typ = IOREQ_TYP_U32_WR, .code = F_PRINTC },
+    { .syscall = IOREQ_MILLIS, .typ = IOREQ_TYP_U32_RD, .code = F_MILLIS },
+    { .syscall = IOREQ_GETC, .typ = IOREQ_TYP_U32_RD, .code = F_GETC },
 };
 
 void disableRawMode(void) {
diff --git a/precompiled/fib.bin b/precompiled/fib.bin
index 1786739d5ea12638ef76b28f599b1f5d4f4df87e..9d95c6d11e29c3aa485af1a9ee37ad5a117dfe32 100755
GIT binary patch
literal 476
zcmZvZPfG$p6u{rxoiW!g$^>16-5L?K2*N%<euOSvr8Wy8*ih=c%eIK#Vosg>3f;Qq
zp)b%E@K{mc21!Ary;<E`bD2Nyz2E!Ij4T&m0{iPK>x(WdhRSjf5eL0L^8p0nOl}7t
zSRQ2U24rOeWqB9n<^f9Q2<1)zWT}C|;-D-5#TclZ17ekdd)PNZXM|=cz>spxDq>h2
zfmsV6tTn*gLd`dHANOfs)CYU0cn$=A5R-WLrTUEet`Rc_Ufldqkp(V0K^4(?lGB`u
z0i)RXH}y;$wV(DPSH;MyM|WZw@^h%qtx@myKyhoyus_raIbVOy1+$1{&;D~xJ!ziH
zQb6_eHpJE*Qomz7d{;cbWRBkiXF&G`Vu8ry7x{?j#lz`62VZkk#EXL8rS&g@`^F@;
sUz0eUtLU*v`{#r~F{+_@`+M<I0H^KaO4T{{yo+?*X}Oo3Zu_bQf5hf`YXATM

literal 252
zcmXv}u}Z^G6g>&NcX5%(9UL17h|c|y4xJTzR0#+vebo7Z;OiK;;M&m-aOmt{^9gSL
zLbIexCGn*;cR7c1?me8FU0q-YcV;J!aT=inq5<{<Q7L#uFw+K)4lq9r#`+sJ*|KN?
zlZN<96!oYzZxq>b%Yk<`sRFKBrWEG(9UuM+wyao`2CJsyR|+@lw$Bv8(PN$b=PLBx
zFGo?gA-F7b6i?^2+%PK_@9NRM*Tq*y?IryTnJy0dQBmI=hCh0I$nURj(x;-B4}38*
K%Z1IKXZQnNPfN%E

diff --git a/precompiled/helloworld.bin b/precompiled/helloworld.bin
index 3fca079c8b17bfd2b490d6caf97c4722a430962b..07ed4a216a07f9a0d4fdb9b26bb5081c5e878459 100755
GIT binary patch
literal 48
wcmY#Z6J&VLz`!_}qd~Zs0Rn_s85kzBFJPF=aR4kP%qq(8SnBJ)^ach70MK>{BLDyZ

literal 60
zcmY#Z6J&VLz`$4>&>+kJ1>4yf8YZ{1GZ#<TE}Y%~6NS(osX00M3g!7lIVlVPQ!5Me

diff --git a/precompiled/mandel.bin b/precompiled/mandel.bin
index 2f7f7402c46bcd9c3e9eceac5616bffe2033233e..b64645a8be943d37439b6b1faf442be6015c87e7 100755
GIT binary patch
literal 236
zcmY#Z6J&VLaDZVlM}u%N0|SHk*Z=>wivsCq|Nl>B`@ks7e)Y`cc2i?vj<RQyn@l&G
zJ2NmOpLotOnVEwj`4kiTWDW*~$*c?v!hAp)h=ti0n1or`{v|(J#$wzm%9xzD7|3T}
zFz!3Yytz-*aWcmQusy<Y`y4j+)iD_Jy<^zidXIVX)uRl?tml{~M;ry3A;ysZ;r?%+
z*&;x*7(nit+$_xb_*T&mVb%pew=#%;#Dv+WOFq8y{F^x|LxV6YE8k>}4Pdj=8-S8f
R;E|e>ldn*oUzC%=002VFMkoLP

literal 204
zcmY#Z6J&VL(7;d}&>(F7?f?Jn;tUMt&;S1yX8pjp-IaksnC;q`$!+Gw!tCYGCbye!
z7Uo#MkbLGC+hh)QhU7!f*(Ngs)qpS`1H)txW@2Cx?q~X!ocEO3n7^1I`4y1vJIB14
zuh^kDV1lr4+&+iReR7P(eCHU9o9{6T2OnnG%zTb{^5w$}lbeJX@;}7?DW1S2GPy&7
z^YJC|-^BtPBEoFbBp=^6_QRZ&p+T6Hm8V!>t8jV)0~mOu=H%onl;;=aq%Z&g0eM7`

diff --git a/precompiled/zigtris.bin b/precompiled/zigtris.bin
index 9ce1ebb77919c4daaae4b11cb0e76c4d143b75c3..96ccb8f64f73c5c79383cc5d114ec8714aef57e8 100755
GIT binary patch
delta 4346
zcmb7H3v8Ul5uX3C|GoaZTyA}STuCrqpK(H*BCf$HlyU)|gBucDN}`m96mg_Hgc>Ab
z8eYBMy8L!*pM#Sn1V}_}>~j-Cf{<~qG_87u8q$!EP>HHfC2&Np#LE&jHHztV_W%D2
zcAwPJ@420wot>TeW_EUe>Vs5})h&dN0dD1PgWeASyYwqlFR*GAXm~S>npvQv38)6@
z-fDnJ!>CACkAqU%4pfq)I}HHZ7KS7cxiJ9-CFbWjq}-f1O|>{wP=Gt()qCd8tv^n+
zR%cGR8}-bx<qKuDtX*bHcgd`N*J}+4N6p(G<(g4lNApRl8EA?Mwi%G)VIn1;Aj`N4
z(6|P-_W6p9Vf?)WAlHIxx>`>1mC|7JjlDr(IBc+1JVO=>E!^|~?LckTT>R19a)rkc
zjNizs<;XS0gO>bm5}{hq+SxwXdPmGy=ge19?Y=qln@jW8^GD>!&Cq6vJx<Ezt9jcI
z%U|crhvus}Tbgfn=7SVX=EU!qY;56Eb8Nnr2bFKian4(nH4PvB2cPv?s-7S+CFrBg
zB21*nk1Dsz<Y~T4T`d*)RyCE#q-$H0bkw8p?PYkdE@h6RZsa1`I|-x{zxF4eA!tz$
zSap}q0x#=ZAP;QmQ!)#9biR^Y*_fg0r&n=vx~L4PiZa}!@Ubw&5K}SL1Zr+qxCp2n
zf))!$Wdzs(K0?-|gpJ%iWnr?h4Gab(LwzK}>R&8pOQmv3qzY&08mgip+X)(5;=#A5
z2YFp{dHL(87kS-tdB$q0`6RaN5{WIpQexF>6jpPKlB<K10Nu}6?Hj=A{s^qT2T!&S
zSnYE%t2-jw0PC7{uzr|#c_gZB!ZUfC^W@!PGm0QBl#?a_Ozum(l8XwbZ(h>agn(7m
zVy+hRr(<aQ7r@RR76%_C-p8R4k+0M>pV{rYOuC=PTvuO{KfuX=oO=kBbbB+@^ae1=
ze5__bc9L^wFJ|zhkv}SwD8t>59zKRx_eR+B$12(3KU89vEBSF(BsEe?J^kpk?kegH
zLelHes9A~yR9UeI5n0K0SD}h3j*b=hoisF168O8V4HyjJc}r{ZVcNC=k|KV-rs5a;
zc$tv3_!{z6M3m>VVj&gr%;4r2vGx!bN~VfMEG`dX1Os!%+n8G_SBCH$L&s3I6~Qqg
zvk|XMySfoP?U*!il@fHiRh(cqHIKQ_Sm76yEgNw7Mjz|<>g-wkhVUEq>Ig5y?ST=U
zjdbhm`KNWZ)2rJ?<R3mCxe%#l)fXw;gXw}06jhANQ^m$>kt#tKRYB%zwIl*XHLciq
zJyKmiElLpgP671-q5eMLdQhT)`&{f<l2H=b)2x0V1u;*Zlv{@j76i524X6;}8uw$R
z>1fe%t8v`fIZNHGK&KZ$AwcRyL`(S~a4lrHJ6I<8qHa@PdN$dy-c6^c7bIcAm2{sa
zNjWShp-tuFQdd$PlauA9CLpV1Q)YpiW?>6}YBS8UI6jMG#Tmbc<M(hZb3ecqh$~9=
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zYtGB+D66Av%8$bS9U<zffWrRf&nO9F_tNa)c<U4v@A*{8_Udf;03sN}v2*~^hx~q#
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z5{PUtZu#=MSG?&g?XYx*NMNpRrEc7T3LN4e2-P=zdDYoB?Rx=Ij@jCL)vHRXhxx4w
zA}M3-|5m*T>{FYk9M#(_)m~B~>V*JdBYu>0o=HcsM%0<0L?<9!=aZC+JI~nn>T`HS
zbpWe50&Hj!f#;JZL4(GWD6d#%trCl6^Pj8amZ=N(*an)jN+N*;W?JIJfWk-F*JwBj
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zC5!2dc%fnJUQnq>=Pgq|`rIl=*2R@yg+}EOTZ)CZwiO^ShEBFpIDI}v;|oeDtVG8p
z#2dC^0&g#3cQIb->{7d}>LwG+?QyL0(?ubK8HH{vMJnEB$>>D0WCX~CqUA5nk%667
zJt$RBnN-@cXKj7GWR7gS$I_<~Io*)LO?w+Gh4VLsE=%YFQdTOltbR<vyMa=2Dc%tV
zt_eC<d445&<OPmKm5QB>?s!q0T+}3NJ~Qn3tc>e|>F9U}4~KeA!QPbJ3q(aFYJ31e
zq-mLS^fedXlfcI4Cs=5SyHs1ajKxc9ol{>7?R<T~-r>L27j@&e2i2KYM%=A~WJjx2
zUqA{h`?m!~LtzbtT`26@(Q4P1jv3w`Do?>_0sg{b@}_W%k{}trHVo*1lj5-Kz#;ix
z9g+XAggb=NK0BGn8FZH2L|XS8Tw^6wISFul<xp%xY}`+u<KA)9xd~{wSIYUVCzAFX
z(aBLCkI<S0+*b|BO;5Y&{;y%P-NV<=$X7b{#StV}8L@Fdm{YCPyBWv0K^L#>mI}t!
zb4pZ)!o3G)VxEI>>j9u=ps;=GXK3Z$Z7Z|*e8Y`It7}^sJD-hFBBi6InB(u$?n~~*
z;CWt7iv|tb>{6%yR*c*&VLOlQOFu^3W3?~*$ubsxi~0bw>miBvv;ft;_^$M-{8U**
z>J1?`O1>*G!(Jy^o><R464hsmyr%~WW%?|QTmiA}7Ad{tSW#KpT^#j(UE)3!FC7*0
zOuU}F*j}CQ&?lJToo_?Wxng0zZ#HIj$uY87V*NwFcB_!C<{QGBrNjK^;fL}6%JSp9
zuM%HdL;O_b!|3THysYAOInVjFie}l^#q&t=-P~Py8*i!lD!-#L$hTEpxaf1Pi7Qz{
z8#Jg;#LM{Ft1ZAp$y5BLs>aF;b;a=-{8WzZAX3ad1Kibzy@h*Ji99CDuV(q<7u+mE
zKcBi_oecX%<BNW$UUWwgj9=;VzoW?eDSr8dU>qG?Rr8%nX<~HG6_Zk+tP+erg>j||
zXR3JjH!e@zTV}I9K=w`Ln8eOs`_*7zIG`7)7wL&_+T-;&#u5*AIb)7=0geZeV#Y!f
z&f}8~Le9E_$j9doY(*ME3dmoG<oif*d^5a@6JmoWk>N%<fK*3Xk5nlBCC-ZtlQ<S~
rhmnd6K1DvJ1T1p+E0GF=w;~nmJ4c_o>SL)acoi5&HsZO&8t3mHckat%

delta 4288
zcma)9eQ;FO6+iFezWrX7y_*oWfH8M>jYueV#f*ZoNH$3Q3RRqf+DTm*Kk772F_qSj
zeem{!WKlvdV5*FQBpHLL1G6yEcBZq~1T=n>Kh$wRg_$iyJIt7w8VE>D&wcwg8(VGN
znYZ`dbI(2J-1G4}_nk@ZOuAWQI(z|zyVkYnbgOTXw0G;xK{@8%`oJYujt|B`=jq{N
zRExn33UEIxd#Vv>l%%b-RY$1SVyziZY<+D>+*<hH^TB4^oM|4Rnhunx@N6x>X}z$Y
zR}m?(gUsV9K;um)%;mb!ScUJG0}QUfJsm4X_+n|#&ksNA6Fc+=%^fe0IYJ6gJAh_T
znz;t+&9yFE(|o3ulF4yvZ(*&qKC80VZS9Rc%46~jhs6o^^42M{R<6szWTDO6zKsOF
zDgFa%Q|xYQ-A}bgrl>zvUSDIa`zV^tiKndkA(P%syx%UjaHqM>XDZjo@C?60xvAl^
z?{H_<<lI4IO3;04MZCxb{*H35oZikCsLQ1be7%~CXN}NXiV^Nmcq)K~I@BpXyoI+{
zLE;$#Mtp@g@d80ZeZWE;ZYIC(ZG!@^`M;N$?C|o%WKm<5t{Pj)(_<4#PfAhxh7^9V
z3Zm&=h^lFzX;tMS)}`n)Q6V`%fDQ0h$*sx8b`frp<s=8|y2hvx&H=NN46EN?&E`tg
zlt?qIt<6+LLsA5dEz=53)Pb~)sWg2Vbt0{EDlK*c)p8Q6y+UDiixd{RNnw$@l)(rj
zF&_^fVD)bUn|mDCJXAjad0_Rg$ZYPP<U!0up39xHlD?nkToTn<@l39A*k%c36!W)O
zLt-LlsVn}*U|2YPZK$yc52vaZ217{C^rR{|ulI}K<cV_|G-6RGk>=xEwf#s+@J8E`
z8}vP#?3M=~MJXvYOVcS#ikOSd-ECD&?8RrnteiK66s1p<jJ_s`r&B?;YbeNGdOwJ9
zuHi>*!DJ}R9lL;bs6p!VL88;4VW=(R3js42ej+QqY7j*PIeJ#)-)UU~C64dy?ZBW%
zq=&UfpHABsmICN%nyAphCwR@kYDiZD7?txA#pH92aa1l*vcb=VkkN?=tl!^Y2)$G0
z>zQ4uR(e!P>2E^b7R-(wnZ2sYyhCKq1}vtSDhkFzjLkINWJhC#UsM*E^h=KQsBYGW
z&&&AiRozJ{5_h1-&0bBp*{;wuwo&z#j3_)l8M*+O#p<t=s2l4A^HJa#-;@HraR{ga
zzQJV}Mz7Dt-5`r-QBAvGh4$Fs6&PB_C{Pa&?(72Y@JVbh$tdyOW2|m>67sHJOWga2
zt?@P#I?bmI#&GnYQS+xuY~D(A?akWYa-?Om=cv5}_}FYHZYH61UE_3Jmp@?i4uRmO
zoyNJu_*y$XJ2ovLe`rf|juAY)me@EfC-h-_Utmk5@O{U2n=sM{XFjD`GV^I0fNBv=
zQY~{5=ZZByf%6kMm$?U^4PuJXtA9c>`X{2qjqsL_skY@~Bhn1YWf@Q+htZSyv#jnI
zLcu?PMMgjwNI~L(v}6n)LBrdjxRH#BidMq$EG2O*k^JRAop32lldRD&j4?@PEe!u>
zlpK^2Po**5h`*(L?lBV*%bfM4Jj!sBx9pjOlgu&xkaCyy7QQIcO&L$5XNx*OPa*oG
z6r)d7scjcTv!~>me0B(5P6OZ34EgN)z_o0UW|ymcma9Sg`x;36?L5ED6_v40Qm%|s
z^`Ha~mV$=|+?OU_K7bZu@(c{&qbedJMaC&%NirG^Vdp8sci|469`az8%T|Uj#;i4Y
z=_HT-6Qj3;kCR!7$tYx50QaFdefeYwJAnlvdxiVhrrwMqeC&xq!cDHWlssl0JG@k)
z-dZW)EGYbA_xy#!|N1U(e2X)@!WjwoKEA{gsrciv<iW3m5QG$OIpY&r!NE1m_AG&f
zeV5HxZUg1bT#BiZKX3mK__@b`uCIZ-?MpC@*dS_uK#6X$OUzkM_c+J>%w_lQadlH`
zk8JMAWXwI2yl&)mBX81!%${yaZ8M;_v+q15RY0|72gj~boHKk50n3Bsg}~M1VYRzu
z%neWJ8Zvx@g?9TzBoG(;tbQxSHX`O`L$;9oP0Qmi3FJ-$v6<s~X)QiNGag8m7-IV@
z2EP$L<X0j~DJ8WQh`~MIU*W>HEQQaT^8DE4rzk|ZvZb%zT2Hzw3S(u3cYc3`y=8^l
ztOFqIS5Bxzq_V=Y2h@tbR@9diFb%i;e}%13a$EXs>x5663W0<Krif&2#D|jXaU&c@
z3`v6$9tI=gl$6V|$606uabz#Hune%eKO(-IK1+#HI-LX!1ne61ha{tJgCt<sgy8=`
z(zekPJ4!~T&nfXZ(DpHj6CH|YdJog8FqAqmsY9GV#RRXb#579jMYOFt2z1p!FdCMM
z`;D#WKKP|5u;QHUf5E<ipky{HXclEzRLL7kFG2$*9Ie9Z4GI*{&^G!amRp%OwybUR
zk^&~DDiW4Ixe(#K1OvuonHOA>Fc8`=vCw`+@UXi5GOImgg$0sZOeAy@rxIQ&b25gl
z7MVi((OO9s8Cr6;zS-onm-(<tEWQd)tkdMth`l81)TFEm4{S1dRH6x*(U3%?PdAvt
zrhr`9WbzS>4IEIgU*IVhVBgS@&u4inwg^42k6Wj%fSZ0%32y+lt49_6#(c*X|KEIY
zL4=?!IeOxiN=6<n3y+kL4SWCgIONj@5TMfbGC*+|!BK0mS3s((0#bOt_@5x9*00>7
zj<+ykZ`nh-S0+uA0?GTWD5W8@hRil(wso&8fz*yEAQi_XT6MORKe3adB8s!fduC^h
z<6ZZbD!{~juT(kYIJT71mC|g2vDL``Ln%>Byj&HR3;Yhk3kfA-XSw4Lx~vswwNo0z
z9?vt{yW(2MoqP?gn?_x=kZ66*PIq1f(NrhT(cllX=VO==eriK5ytPto@+STkFVH!+
zbVx=0zOR(98;TG2k4GK-G4pf4y%~zB`_5x_e_gV&7r*N85+W|XB`beCS$1I}8R4{8
z<5vVa*=n@a@%mHZYDl&6J-P7LD0xs~Sbgh!{gj^!u;fwd0_^j@m3VFiP`48sn^QJ=
z-<~k`qMc%Q#%X0aj6}(5DVlo-uV@!1CZ*(ZP^@uZq`_+;+POk9E+3gt=5|ixo!3a*
zr9wi*ZjEv{aiXm91vWO!bSGNjL^E<<O%%IaU-O++k4gPJQ2jXmcU8Z`7u5VphTXiU
zrdck$z|Y_S-TbPV_qebn-mha!Fx`1ebuGVp#`UtE<2z?O&iTv+esty~(l{TT8I;r8
zxI5Tblcly8HpH`XbQ6)H_Hp30E}-^J`MZK!WZC#LKQn8MTzHM&IQv$)kk5C|{z%17
z-qP=8ALuW;zxfOxZ6`k4rsJ63T6cSm)Sf?e?P<yTSvBaXD$wt%0sY|`er)m8$$5bi
zX&aI+;!_rU<r2`*^>7`IP8^@SzBDH|N6dyAYrYJ}X*j<fM?5%ui6ef*!5cV=eXDWA
z4;~2N=*Mv%j?;0RgK}`b27YHT-iQP{F08~6uh{Sr(uLqQ9EC!PbRqC(I0^-QNXM*)
hcdh-O;V29aS^FFFpI`Td6euhP{TDyQbBR6H@83(6#cu!r

diff --git a/uvm32/uvm32.c b/uvm32/uvm32.c
index 8f1422d..10f75d3 100644
--- a/uvm32/uvm32.c
+++ b/uvm32/uvm32.c
@@ -66,8 +66,45 @@ bool uvm32_load(uvm32_state_t *vmst, uint8_t *rom, int len) {
     return true;
 }
 
+// Read C-string up to terminator and return len,ptr
+static void get_safeptr_terminated(uvm32_state_t *vmst, uint32_t addr, uint8_t terminator, uvm32_evt_ioreq_buf_t *buf) {
+    uint32_t ptrstart = addr - MINIRV32_RAM_IMAGE_OFFSET;
+    uint32_t p = ptrstart;
+    if (p >= UVM32_MEMORY_SIZE) {
+        setStatusErr(vmst, UVM32_ERR_MEM_RD);
+        buf->ptr = NULL;
+        buf->len = 0;
+        return;
+    }
+    while(vmst->memory[p] != terminator) {
+        p++;
+        if (p >= UVM32_MEMORY_SIZE) {
+            setStatusErr(vmst, UVM32_ERR_MEM_RD);
+            buf->ptr = NULL;
+            buf->len = 0;
+            return;
+        }
+    }
+    buf->ptr = &vmst->memory[ptrstart];
+    buf->len = p - ptrstart;
+}
+
+#if 0
+static void get_safeptr(uvm32_state_t *vmst, uint32_t addr, uint32_t len, uvm32_evt_ioreq_buf_t *buf) {
+    uint32_t ptrstart = addr - MINIRV32_RAM_IMAGE_OFFSET;
+    if (ptrstart + len >= UVM32_MEMORY_SIZE) {
+        setStatusErr(vmst, UVM32_ERR_MEM_RD);
+    }
+    buf->ptr = &vmst->memory[ptrstart];
+    buf->len = len;
+}
+#endif
+
+
 uint32_t uvm32_run(uvm32_state_t *vmst, uvm32_evt_t *evt, uint32_t instr_meter) {
     uint32_t num_instr = 0;
+//    uvm32_evt_ioreq_buf_t b;
+
     if (vmst->status != UVM32_STATUS_PAUSED) {
         setStatusErr(vmst, UVM32_ERR_NOTREADY);
         setup_err_evt(vmst, evt);
@@ -79,7 +116,65 @@ uint32_t uvm32_run(uvm32_state_t *vmst, uvm32_evt_t *evt, uint32_t instr_meter)
     // run CPU until no longer in running state
     while(vmst->status == UVM32_STATUS_RUNNING) {
         uint64_t elapsedUs = 1;
-        if (0 != MiniRV32IMAStep(vmst, vmst->core, vmst->memory, 0, elapsedUs, 1)) {
+        uint32_t ret;
+        ret = MiniRV32IMAStep(vmst, vmst->core, vmst->memory, 0, elapsedUs, 1);
+        if (3 == ret) {
+            const uint32_t syscall = vmst->core->regs[17];  // a7
+            uint32_t value = vmst->core->regs[10]; // a0
+            bool syscall_valid = false;
+            // on exception we should jump to mtvec, but we handle directly
+            // and skip over the ecall instruction
+            vmst->core->pc += 4;
+            switch(syscall) {
+                // inbuilt syscalls
+                 case IOREQ_HALT:
+                    setStatus(vmst, UVM32_STATUS_ENDED);
+                    syscall_valid = true;
+                break;
+                case IOREQ_YIELD:
+                    vmst->ioevt.typ = UVM32_EVT_YIELD;
+                    setStatus(vmst, UVM32_STATUS_PAUSED);
+                    syscall_valid = true;
+                break;
+
+                // user defined syscalls
+                default:
+                    // search in mappings
+                    for (int i=0;i<vmst->numMappings;i++) {
+                        if (syscall == vmst->mappings[i].syscall) {
+                            // setup ioevt.data according to mapping typ
+                            switch(vmst->mappings[i].typ) {
+                                case IOREQ_TYP_VOID:
+                                break;
+                                case IOREQ_TYP_U32_WR:
+                                    vmst->ioevt.data.ioreq.val.u32 = value;
+                                break;
+                                case IOREQ_TYP_BUF_TERMINATED_WR:
+                                    get_safeptr_terminated(vmst, value, 0x00, &vmst->ioevt.data.ioreq.val.buf);
+                                break;
+                                case IOREQ_TYP_U32_RD:
+//                                    get_safeptr(vmst, value, 4, &b);
+                                    vmst->ioevt.data.ioreq.val.u32p = &vmst->core->regs[11]; // r1, //(uint32_t *)b.ptr;
+                                break;
+                            }
+                            vmst->ioevt.typ = UVM32_EVT_IOREQ;
+                            vmst->ioevt.data.ioreq.code = vmst->mappings[i].code;
+                            vmst->ioevt.data.ioreq.typ = vmst->mappings[i].typ;
+//#warning FIXME, retval
+//                            vmst->core->regs[11] = 456; // r1
+                            setStatus(vmst, UVM32_STATUS_PAUSED);
+                            syscall_valid = true;
+                            break;  // stop searching
+                        }
+                    }
+                    // no mapping found
+                    if (!syscall_valid) {
+                        setStatusErr(vmst, UVM32_ERR_BAD_SYSCALL);
+                    }
+                break;
+            }
+        } else if (ret != 0) {
+            // unhandled exception
             setStatusErr(vmst, UVM32_ERR_INTERNAL_CORE);
             setup_err_evt(vmst, evt);
         }
@@ -115,83 +210,6 @@ uint32_t uvm32_run(uvm32_state_t *vmst, uvm32_evt_t *evt, uint32_t instr_meter)
     }
 }
 
-// Read C-string up to terminator and return len,ptr
-static void get_safeptr_terminated(uvm32_state_t *vmst, uint32_t addr, uint8_t terminator, uvm32_evt_ioreq_buf_t *buf) {
-    uint32_t ptrstart = addr - MINIRV32_RAM_IMAGE_OFFSET;
-    uint32_t p = ptrstart;
-    if (p >= UVM32_MEMORY_SIZE) {
-        setStatusErr(vmst, UVM32_ERR_MEM_RD);
-        buf->ptr = NULL;
-        buf->len = 0;
-        return;
-    }
-    while(vmst->memory[p] != terminator) {
-        p++;
-        if (p >= UVM32_MEMORY_SIZE) {
-            setStatusErr(vmst, UVM32_ERR_MEM_RD);
-            buf->ptr = NULL;
-            buf->len = 0;
-            return;
-        }
-    }
-    buf->ptr = &vmst->memory[ptrstart];
-    buf->len = p - ptrstart;
-}
-
-static void get_safeptr(uvm32_state_t *vmst, uint32_t addr, uint32_t len, uvm32_evt_ioreq_buf_t *buf) {
-    uint32_t ptrstart = addr - MINIRV32_RAM_IMAGE_OFFSET;
-    if (ptrstart + len >= UVM32_MEMORY_SIZE) {
-        setStatusErr(vmst, UVM32_ERR_MEM_RD);
-    }
-    buf->ptr = &vmst->memory[ptrstart];
-    buf->len = len;
-}
-
-void uvm32_HandleOtherCSRWrite(void *userdata, uint16_t csrno, uint32_t value) {
-    uvm32_evt_ioreq_buf_t b;
-    uvm32_state_t *vmst = (uvm32_state_t *)userdata;
-
-    switch(csrno) {
-        case IOREQ_HALT:
-            setStatus(vmst, UVM32_STATUS_ENDED);
-        break;
-        case IOREQ_YIELD:
-            vmst->ioevt.typ = UVM32_EVT_YIELD;
-            setStatus(vmst, UVM32_STATUS_PAUSED);
-        break;
-
-        default:
-            // search in mappings
-            for (int i=0;i<vmst->numMappings;i++) {
-                if (csrno == vmst->mappings[i].csr) {
-                    // setup ioevt.data according to mapping typ
-                    switch(vmst->mappings[i].typ) {
-                        case IOREQ_TYP_VOID:
-                        break;
-                        case IOREQ_TYP_U32_WR:
-                            vmst->ioevt.data.ioreq.val.u32 = value;
-                        break;
-                        case IOREQ_TYP_BUF_TERMINATED_WR:
-                            get_safeptr_terminated(vmst, value, 0x00, &vmst->ioevt.data.ioreq.val.buf);
-                        break;
-                        case IOREQ_TYP_U32_RD:
-                            get_safeptr(vmst, value, 4, &b);
-                            vmst->ioevt.data.ioreq.val.u32p = (uint32_t *)b.ptr;
-                        break;
-                    }
-                    vmst->ioevt.typ = UVM32_EVT_IOREQ;
-                    vmst->ioevt.data.ioreq.code = vmst->mappings[i].code;
-                    vmst->ioevt.data.ioreq.typ = vmst->mappings[i].typ;
-                    setStatus(vmst, UVM32_STATUS_PAUSED);
-                    return;
-                }
-           }
-           // no mapping found
-           setStatusErr(vmst, UVM32_ERR_BAD_CSR);
-        break;
-    }
-}
-
 bool uvm32_hasEnded(const uvm32_state_t *vmst) {
     return vmst->status == UVM32_STATUS_ENDED;
 }
diff --git a/uvm32/uvm32.h b/uvm32/uvm32.h
index 4caaa7b..9a55b76 100644
--- a/uvm32/uvm32.h
+++ b/uvm32/uvm32.h
@@ -13,7 +13,7 @@
     X(UVM32_ERR_NOTREADY) \
     X(UVM32_ERR_MEM_RD) \
     X(UVM32_ERR_MEM_WR) \
-    X(UVM32_ERR_BAD_CSR) \
+    X(UVM32_ERR_BAD_SYSCALL) \
     X(UVM32_ERR_HUNG) \
     X(UVM32_ERR_INTERNAL_CORE) \
     X(UVM32_ERR_INTERNAL_STATE) \
@@ -40,9 +40,9 @@ typedef enum {
 
 typedef uint32_t uvm32_user_ioreq_code_t;
 
-// user supplied mapping from csr to typed ioreq
+// user supplied mapping from syscall to typed ioreq
 typedef struct {
-    uint32_t csr;
+    uint32_t syscall;
     uvm32_user_ioreq_code_t code;
     uvm32_ioreq_typ_t typ;
 } uvm32_mapping_t;
@@ -75,11 +75,9 @@ typedef struct {
     } data;
 } uvm32_evt_t;
 
-void uvm32_HandleOtherCSRWrite(void *userdata, uint16_t csrno, uint32_t value);
 #define MINIRV32_DECORATE static
 #define MINI_RV32_RAM_SIZE UVM32_MEMORY_SIZE
 #define MINIRV32_POSTEXEC(pc, ir, retval) {if (retval > 0) return 3;}
-#define MINIRV32_OTHERCSR_WRITE(csrno, value) uvm32_HandleOtherCSRWrite(userdata, csrno, value);
 #ifndef MINIRV32_IMPLEMENTATION
 #define MINIRV32_STEPPROTO
 #endif