gba: add support for mGBA debugging

monitor.go

@@ -278,7 +278,7 @@ func ListSerialPorts() ([]SerialPortInfo, error) {
 	return serialPortInfo, nil
 }
 
-var addressMatch = regexp.MustCompile(`^panic: runtime error at 0x([0-9a-f]+): `)
+var addressMatch = regexp.MustCompile(`panic: runtime error at 0x([0-9a-f]+): `)
 
 // Extract the address from the "panic: runtime error at" message.
 func extractPanicAddress(line []byte) uint64 {

src/runtime/runtime_arm7tdmi.go

@@ -1,4 +1,4 @@
-//go:build arm7tdmi
+//go:build arm7tdmi && !mgbadebug
 
 package runtime
 

src/runtime/runtime_mgba.go

@@ -0,0 +1,121 @@
+//go:build gameboyadvance && mgbadebug
+
+package runtime
+
+import (
+	_ "runtime/interrupt" // make sure the interrupt handler is defined
+	"runtime/volatile"
+	"unsafe"
+)
+
+var (
+	// Setting this memory address to 0xC0DE enables mGBA's debug printing
+	debugEnable = (*volatile.Register16)(unsafe.Pointer(uintptr(0x4FFF780)))
+	// mGBA supports log levels from 0x100(fatal) to 0x104(debug)
+	logLevel uint16 = 0x104 // use the debug log level
+	// Once we are ready to output we set the debug flags register to logLevel
+	// mGBA will output the text and then clear the text buffer when set
+	debugFlags = (*volatile.Register16)(unsafe.Pointer(uintptr(0x4FFF700)))
+
+	textBuffer = (*[255]byte)(unsafe.Pointer(uintptr(0x4FFF600)))
+	index      = 0
+)
+
+func putchar(c byte) {
+	if c == '\n' || index >= len(textBuffer) {
+		debugFlags.Set(logLevel)
+		index = 0
+
+		// mGBA automatically prints a new line so we can ignore it
+		if c == '\n' {
+			return
+		}
+	}
+
+	textBuffer[index] = c
+	index++
+}
+
+func getchar() byte {
+	// dummy, TODO
+	return 0
+}
+
+func buffered() int {
+	// dummy, TODO
+	return 0
+}
+
+//go:extern _sbss
+var _sbss [0]byte
+
+//go:extern _ebss
+var _ebss [0]byte
+
+//go:extern _sdata
+var _sdata [0]byte
+
+//go:extern _sidata
+var _sidata [0]byte
+
+//go:extern _edata
+var _edata [0]byte
+
+// Entry point for Go. Initialize all packages and call main.main().
+//
+//export main
+func main() {
+	// Initialize .data and .bss sections.
+	preinit()
+
+	// Enable mGBA debugging.
+	debugEnable.Set(0xC0DE)
+
+	// Run program.
+	run()
+}
+
+func preinit() {
+	// Initialize .bss: zero-initialized global variables.
+	ptr := unsafe.Pointer(&_sbss)
+	for ptr != unsafe.Pointer(&_ebss) {
+		*(*uint32)(ptr) = 0
+		ptr = unsafe.Add(ptr, 4)
+	}
+
+	// Initialize .data: global variables initialized from flash.
+	src := unsafe.Pointer(&_sidata)
+	dst := unsafe.Pointer(&_sdata)
+	for dst != unsafe.Pointer(&_edata) {
+		*(*uint32)(dst) = *(*uint32)(src)
+		dst = unsafe.Add(dst, 4)
+		src = unsafe.Add(src, 4)
+	}
+}
+
+func ticksToNanoseconds(ticks timeUnit) int64 {
+	return int64(ticks)
+}
+
+func nanosecondsToTicks(ns int64) timeUnit {
+	return timeUnit(ns)
+}
+
+func ticks() timeUnit {
+	// TODO
+	return 0
+}
+
+func sleepTicks(d timeUnit) {
+	// TODO
+}
+
+func exit(code int) {
+	abort()
+}
+
+func abort() {
+	// TODO
+	for {
+	}
+}