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Make yield a regular syscall taking an argument.

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Allows "wait for interrupt"/"wait for event" type operation where VM code blocks until the host has something for it.
This commit is contained in:
Toby Jaffey 2025-12-10 10:35:18 +00:00
parent d52baca7b2
commit e07eeab043
14 changed files with 88 additions and 24 deletions
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40
README.md
View file

@ -203,6 +203,46 @@ The following functions are used to access syscall parameters safely:
void uvm32_setval(uvm32_state_t *vmst, uvm32_evt_t *evt, uvm32_arg_t, uint32_t val);
uvm32_evt_syscall_buf_t uvm32_getbuf(uvm32_state_t *vmst, uvm32_evt_t *evt, uvm32_arg_t argPtr, uvm32_arg_t argLen);
## Event driven operation
A useful pattern for code running in the VM is to be event-driven. In this setup the program requests blocks until woken up with a reason. This requires some support in the host, but can be implemented as follows.
In the VM code:
```c
while(1) {
// ask host to suspend running until one of the following events
uint32_t wakeReason = yield(KEYPRESS_EVENT_MASK | MOUSE_EVENT_MASK | NETWORK_EVENT_MASK);
switch(wakeReason) {
...
}
}
```
In the host code:
```c
uvm32_run(&vmst, &evt, 1000);
switch(evt.typ) {
case UVM32_EVT_SYSCALL:
switch(evt.data.syscall.code) {
case UVM32_SYSCALL_YIELD:
uint32_t events = uvm32_getval(&vmst, &evt, ARG0);
// do not call uvm32_run() again until something in the events set is triggered
break;
...
}
break;
...
}
```
Then, to wake the VM once an (eg. key) event has occurred
```c
uvm32_setval(&vmst, &evt, RET, KEYPRESS_EVENT_MASK);
uvm32_run(&vmst, &evt, 1000);
```
## Configuration

9
apps/lissajous/lissajous.c
View file

@ -13,13 +13,6 @@ void movecursor(int x, int y) {
print("f");
}
void sleep(uint32_t ms) {
uint32_t start = millis();
while (millis() < start + ms) {
yield();
}
}
// Absolute value function for doubles
double abs_c(double x) {
if (x < 0) {
@ -116,7 +109,7 @@ void main(void) {
// wait for next frame
while (millis() < framestart + (1000 / 30)) {
yield();
yield(0);
}
beta += 0.05;
freq1 += 0.01;

2
apps/self/self.c
View file

@ -45,6 +45,8 @@ void main(void) {
break;
case UVM32_EVT_SYSCALL: // vm has paused to handle UVM32_SYSCALL
switch(evt.data.syscall.code) {
case UVM32_SYSCALL_YIELD:
break;
case UVM32_SYSCALL_PUTC:
putc(uvm32_getval(&vmst, &evt, ARG0));
break;

2
apps/sketch/sketch.c
View file

@ -25,7 +25,7 @@ void setup(void) {
void main(void) {
setup();
while(loop()) {
yield();
yield(0);
}
}

2
common/uvm32_target.h
View file

@ -56,7 +56,7 @@ static uint32_t syscall(uint32_t id, uint32_t param1, uint32_t param2) {
#define millis() syscall_cast(UVM32_SYSCALL_MILLIS, 0, 0)
#define putc(x) syscall_cast(UVM32_SYSCALL_PUTC, x, 0)
#define getc() syscall_cast(UVM32_SYSCALL_GETC, 0, 0)
#define yield() syscall_cast(UVM32_SYSCALL_YIELD, 0, 0)
#define yield(x) syscall_cast(UVM32_SYSCALL_YIELD, x, 0)
#define printbuf(x, y) syscall_cast(UVM32_SYSCALL_PRINTBUF, x, y)
extern char _estack;

2
host-arduino/host-arduino.ino
View file

@ -57,6 +57,8 @@ void loop(void) {
break;
case UVM32_EVT_SYSCALL: // vm has paused to handle UVM32_SYSCALL
switch(evt.data.syscall.code) {
case UVM32_SYSCALL_YIELD:
break;
case UVM32_SYSCALL_PUTC:
Serial.print((char)uvm32_getval(&vmst, &evt, ARG0));
break;

35
host-arduino/uvm32.cpp
View file

@ -1,4 +1,5 @@
#include "config.h"
#define MINIRV32_IMPLEMENTATION
#include "uvm32.h"
@ -11,6 +12,9 @@
// On an invalid operation, an error is set in uvm32_state_t, but a valid pointer still needs to be temporarily used
static uint32_t garbage;
// magic value for stack canary
#define STACK_CANARY_VALUE 0x42
#ifndef UVM32_MEMCPY
#define UVM32_MEMCPY uvm32_memcpy
void uvm32_memcpy(void *dst, const void *src, int len) {
@ -85,6 +89,8 @@ bool uvm32_load(uvm32_state_t *vmst, const uint8_t *rom, int len) {
}
UVM32_MEMCPY(vmst->memory, rom, len);
vmst->stack_canary = (uint8_t *)UVM32_NULL;
return true;
}
@ -136,6 +142,12 @@ void uvm32_clearError(uvm32_state_t *vmst) {
uint32_t uvm32_run(uvm32_state_t *vmst, uvm32_evt_t *evt, uint32_t instr_meter) {
uint32_t num_instr = 0;
if (vmst->stack_canary != UVM32_NULL && *vmst->stack_canary != STACK_CANARY_VALUE) {
setStatusErr(vmst, UVM32_ERR_STACKOVERFLOW);
setup_err_evt(vmst, evt);
return num_instr;
}
if (vmst->status != UVM32_STATUS_PAUSED) {
setStatusErr(vmst, UVM32_ERR_NOTREADY);
setup_err_evt(vmst, evt);
@ -160,10 +172,25 @@ uint32_t uvm32_run(uvm32_state_t *vmst, uvm32_evt_t *evt, uint32_t instr_meter)
case UVM32_SYSCALL_HALT:
setStatus(vmst, UVM32_STATUS_ENDED);
break;
case UVM32_SYSCALL_YIELD:
vmst->ioevt.typ = UVM32_EVT_YIELD;
setStatus(vmst, UVM32_STATUS_PAUSED);
break;
case UVM32_SYSCALL_STACKPROTECT: {
// don't allow errant code to change it once set
if (vmst->stack_canary == (uint8_t *)UVM32_NULL) {
uint32_t param0 = vmst->core.regs[10]; // a0
uint32_t mem_offset = param0 - MINIRV32_RAM_IMAGE_OFFSET;
// check data fits in ram
if (mem_offset > UVM32_MEMORY_SIZE) {
setStatusErr(vmst, UVM32_ERR_STACKOVERFLOW);
setup_err_evt(vmst, evt);
}
// check canary is inside valid memory
if (mem_offset < UVM32_MEMORY_SIZE) {
// set canary
vmst->stack_canary = &vmst->memory[mem_offset];
*vmst->stack_canary = STACK_CANARY_VALUE;
}
}
} break;
default:
// user defined syscalls
vmst->ioevt.typ = UVM32_EVT_SYSCALL;

2
host-mini/host-mini.c
View file

@ -47,6 +47,8 @@ int main(int argc, char *argv[]) {
break;
case UVM32_EVT_SYSCALL: // vm has paused to handle UVM32_SYSCALL
switch(evt.data.syscall.code) {
case UVM32_SYSCALL_YIELD:
break;
case UVM32_SYSCALL_PUTC:
printf("%c", uvm32_getval(&vmst, &evt, ARG0));
break;

2
host-parallel/host-parallel.c
View file

@ -81,6 +81,8 @@ int main(int argc, char *argv[]) {
break;
case UVM32_EVT_SYSCALL: // vm has paused to handle UVM32_SYSCALL
switch(evt.data.syscall.code) {
case UVM32_SYSCALL_YIELD:
break;
case UVM32_SYSCALL_PRINTLN: {
const char *str = uvm32_getcstr(&vmst[scheduler_index], &evt, ARG0);
if (str[0] != 0) {

9
host/host.c
View file

@ -167,10 +167,6 @@ int main(int argc, char *argv[]) {
printf("UVM32_EVT_END\n");
isrunning = false;
break;
case UVM32_EVT_YIELD:
//printf("UVM32_EVT_YIELD\n");
// program has paused, but no syscall
break;
case UVM32_EVT_ERR:
printf("UVM32_EVT_ERR '%s' (%d)\n", evt.data.err.errstr, (int)evt.data.err.errcode);
if (evt.data.err.errcode == UVM32_ERR_HUNG) {
@ -187,6 +183,11 @@ int main(int argc, char *argv[]) {
printf("%02x", *buf.ptr++);
}
} break;
case UVM32_SYSCALL_YIELD: {
// uint32_t yield_typ = uvm32_getval(&vmst, &evt, ARG0);
// printf("YIELD type=%d\n", yield_typ);
// uvm32_setval(&vmst, &evt, RET, 123);
} break;
case UVM32_SYSCALL_PRINT: {
const char *str = uvm32_getcstr(&vmst, &evt, ARG0);
printf("%s", str);

BIN
precompiled/fib.bin
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BIN
precompiled/self.bin
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6
uvm32/uvm32.c
View file

@ -170,14 +170,10 @@ uint32_t uvm32_run(uvm32_state_t *vmst, uvm32_evt_t *evt, uint32_t instr_meter)
case UVM32_SYSCALL_HALT:
setStatus(vmst, UVM32_STATUS_ENDED);
break;
case UVM32_SYSCALL_YIELD:
vmst->ioevt.typ = UVM32_EVT_YIELD;
setStatus(vmst, UVM32_STATUS_PAUSED);
break;
case UVM32_SYSCALL_STACKPROTECT: {
// don't allow errant code to change it once set
if (vmst->stack_canary == (uint8_t *)UVM32_NULL) {
uint32_t param0 = vmst->core.regs[10];
uint32_t param0 = vmst->core.regs[10]; // a0
uint32_t mem_offset = param0 - MINIRV32_RAM_IMAGE_OFFSET;
// check data fits in ram

1
uvm32/uvm32.h
View file

@ -26,7 +26,6 @@ typedef enum {
typedef enum {
UVM32_EVT_ERR,
UVM32_EVT_SYSCALL,
UVM32_EVT_YIELD,
UVM32_EVT_END,
} uvm32_evt_typ_t;