Zig allocator demo, using extram

apps/zigalloc/src/uvm.zig

@@ -0,0 +1,65 @@
+const uvm32 = @cImport({
+    @cDefine("USE_MAIN", "1");
+    @cInclude("uvm32_target.h");
+});
+const buildopts = @import("buildopts");
+const std = @import("std");
+
+const extram:[*]u8 = @ptrFromInt(uvm32.UVM32_EXTRAM_BASE);
+const extram_len = buildopts.heapsize;
+
+var fba:std.heap.FixedBufferAllocator = .init(extram[0..extram_len]);
+
+pub fn allocator() std.mem.Allocator {
+    return fba.allocator();
+}
+
+pub inline fn syscall(id: u32, param1: u32, param2: u32) u32 {
+    var val: u32 = undefined;
+    asm volatile ("ecall"
+        : [val] "={a1}" (val),
+        : [param1] "{a0}" (param1), [param2] "{a1}" (param2),
+          [id] "{a7}" (id),
+        : .{ .memory = true });
+    return val;
+}
+
+pub inline fn getc() ?u8 {
+    const key = syscall(uvm32.UVM32_SYSCALL_GETC, 0, 0);
+    if (key == 0xFFFFFFFF) {
+        return null;
+    } else {
+        return @truncate(key);
+    }
+}
+
+pub inline fn millis() u32 {
+    return syscall(uvm32.UVM32_SYSCALL_MILLIS, 0, 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.UVM32_SYSCALL_PRINT, @intFromPtr(s.ptr), 0);
+}
+
+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.UVM32_SYSCALL_PRINTLN, @intFromPtr(s.ptr), 0);
+}
+
+pub inline fn yield() void {
+    _ = syscall(uvm32.UVM32_SYSCALL_YIELD, 0, 0);
+}
+
+pub inline fn putc(c:u8) void {
+    _ = syscall(uvm32.UVM32_SYSCALL_PUTC, c, 0);
+}
+