gary/debugger/main.go

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package main
import (
"errors"
"fmt"
"log"
"sync"
"time"
"go.bug.st/serial"
)
const portDev = "/dev/ttyUSB0"
func main() {
dbg, err := Open()
if err != nil {
log.Fatalf("connecting to debugger: %v", err)
}
defer dbg.Close()
fmt.Println("Writing...")
if err := dbg.Write(0x42, 123); err != nil {
log.Fatalf("writing to memory: %v", err)
}
v, err := dbg.Read(0x42)
if err != nil {
log.Fatalf("reading from memory: %v", err)
}
fmt.Printf("addr 0: %02x\n", v)
}
type Debugger struct {
port serial.Port
mu sync.Mutex
}
func Open() (*Debugger, error) {
mode := &serial.Mode{
BaudRate: 115_200,
}
port, err := serial.Open(portDev, mode)
if err != nil {
return nil, err
}
return &Debugger{port: port}, nil
}
func (d *Debugger) Close() error {
d.mu.Lock() // note, deliberately no unlocking, to poison.
return d.port.Close()
}
func encode(addr int, write bool, data byte) [4]byte {
writeVal := uint8(0)
if write {
writeVal = 1
}
var ret [4]byte
ret[3] = data
ret[2] = byte(addr<<1) | writeVal
ret[1] = byte(addr >> 7)
ret[0] = byte(addr >> 15)
return ret
}
func (d *Debugger) Read(addr int) (byte, error) {
d.mu.Lock()
defer d.mu.Unlock()
if addr >= 2<<17 {
return 0, fmt.Errorf("read %d out of bounds", addr)
}
packet := encode(addr, false, 0)
fmt.Printf("Writing: %02x %02x %02x %02x\n", packet[0], packet[1], packet[2], packet[3])
if _, err := d.port.Write(packet[:]); err != nil {
return 0, err
}
d.port.SetReadTimeout(2 * time.Second)
n, err := d.port.Read(packet[:1])
if err != nil {
return 0, err
} else if n == 0 {
return 0, errors.New("no read")
}
return packet[0], nil
}
func (d *Debugger) Write(addr int, val byte) error {
d.mu.Lock()
defer d.mu.Unlock()
if addr >= 2<<17 {
return fmt.Errorf("write %d out of bounds", addr)
}
packet := encode(addr, true, val)
fmt.Printf("Writing: %02x %02x %02x %02x\n", packet[0], packet[1], packet[2], packet[3])
if _, err := d.port.Write(packet[:]); err != nil {
return err
}
return nil
}