Allow specifying IO for serial port

devices/serial_port.go

@@ -1,8 +1,9 @@
 package devices
 
 import (
+	"bytes"
 	"fmt"
-	"os"
+	"io"
 
 	"github.com/maxfierke/gogo-gb/mem"
 )
@@ -74,14 +75,27 @@ func (sc *SerialCtrl) SetClockInternal(enabled bool) {
 }
 
 type SerialPort struct {
-	clk  uint
-	ctrl SerialCtrl
-	recv byte
-	buf  byte
+	clk    uint
+	ctrl   SerialCtrl
+	recv   byte
+	buf    byte
+	reader io.Reader
+	writer io.Writer
 }
 
 func NewSerialPort() *SerialPort {
-	return &SerialPort{}
+	return &SerialPort{
+		reader: bytes.NewReader([]byte{}),
+		writer: io.Discard,
+	}
+}
+
+func (sp *SerialPort) SetReader(reader io.Reader) {
+	sp.reader = reader
+}
+
+func (sp *SerialPort) SetWriter(writer io.Writer) {
+	sp.writer = writer
 }
 
 func (sp *SerialPort) Step(cycles uint, ic *InterruptController) {
@@ -97,9 +111,9 @@ func (sp *SerialPort) Step(cycles uint, ic *InterruptController) {
 		} else {
 			sp.clk -= cycles
 		}
-	} else {
-		// TODO: Implement external clock
 	}
+
+	// TODO: Implement external clock
 }
 
 func (sp *SerialPort) OnRead(mmu *mem.MMU, addr uint16) mem.MemRead {
@@ -120,14 +134,17 @@ func (sp *SerialPort) OnWrite(mmu *mem.MMU, addr uint16, value byte) mem.MemWrit
 		sp.ctrl.Write(value)
 
 		if sp.ctrl.IsTransferEnabled() && sp.ctrl.IsClockInternal() {
-			// TODO: derive this somehow and factor in GBC speeds when relevant
+			// TODO(GBC): derive this somehow and factor in GBC speeds when relevant
 			sp.clk = 8192
 
-			// TODO: Write this to some IO writer
-			os.Stderr.Write([]byte{sp.buf})
+			sp.writer.Write([]byte{sp.buf})
 
-			// TODO: Read this from somewhere
-			sp.recv = 0xFF
+			readBuf := make([]byte, 1)
+			if bytesRead, err := sp.reader.Read(readBuf); err != nil || bytesRead == 0 {
+				sp.recv = 0xFF
+			} else {
+				sp.recv = readBuf[0]
+			}
 		}
 
 		return mem.WriteBlock()

hardware/dmg.go

@@ -1,6 +1,7 @@
 package hardware
 
 import (
+	"io"
 	"log"
 
 	"github.com/maxfierke/gogo-gb/cart"
@@ -19,6 +20,7 @@ type DMG struct {
 	cartridge *cart.Cartridge
 	ic        *devices.InterruptController
 	lcd       *devices.LCD
+	serial    *devices.SerialPort
 
 	// Non-components
 	debugger debug.Debugger
@@ -62,6 +64,7 @@ func NewDMGDebug(debugger debug.Debugger) (*DMG, error) {
 		debugger:  debugger,
 		ic:        ic,
 		lcd:       lcd,
+		serial:    serial,
 	}, nil
 }
 
@@ -96,3 +99,11 @@ func (dmg *DMG) Run() {
 func (dmg *DMG) SetLogger(logger *log.Logger) {
 	dmg.logger = logger
 }
+
+func (dmg *DMG) SetSerialReader(serial io.Reader) {
+	dmg.serial.SetReader(serial)
+}
+
+func (dmg *DMG) SetSerialWriter(serial io.Writer) {
+	dmg.serial.SetWriter(serial)
+}

main.go

@@ -17,6 +17,7 @@ type CLIOptions struct {
 	debugPrint string
 	logPath    string
 	logger     *log.Logger
+	serialPort string
 }
 
 const LOG_PREFIX = ""
@@ -50,6 +51,7 @@ func main() {
 
 func parseOptions(options *CLIOptions) {
 	flag.StringVar(&options.cartPath, "cart", "", "Path to cartridge file (.gb, .gbc)")
+	flag.StringVar(&options.serialPort, "serial-port", "", "Path to serial port IO (could be a file, UNIX socket, etc.)")
 	flag.StringVar(&options.debugger, "debugger", "none", "Specify debugger to use (\"none\", \"gameboy-doctor\")")
 	flag.StringVar(&options.debugPrint, "debug-print", "", "Print out something for debugging purposes (\"cart-header\", \"opcodes\")")
 	flag.StringVar(&options.logPath, "log", "", "Path to log file. Default/empty implies stdout")
@@ -110,6 +112,22 @@ func initDMG(options *CLIOptions) *hardware.DMG {
 
 	dmg.SetLogger(logger)
 
+	if options.serialPort != "" {
+		if options.serialPort == "stdout" || options.serialPort == "/dev/stdout" {
+			dmg.SetSerialWriter(os.Stdout)
+		} else if options.serialPort == "stderr" || options.serialPort == "/dev/stderr" {
+			dmg.SetSerialWriter(os.Stderr)
+		} else {
+			serialPort, err := os.Create(options.serialPort)
+			if err != nil {
+				logger.Fatalf("Unable to open file '%s' as serial port: %v\n", options.serialPort, err)
+			}
+
+			dmg.SetSerialReader(serialPort)
+			dmg.SetSerialWriter(serialPort)
+		}
+	}
+
 	return dmg
 }