os, runtime: enable os.Stdin for baremetal target

Author: sago35

Makefile

@@ -396,6 +396,8 @@ smoketest:
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pca10040            examples/echo
 	@$(MD5SUM) test.hex
+	$(TINYGO) build -size short -o test.hex -target=pca10040            examples/echo2
+	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=circuitplay-express examples/i2s
 	@$(MD5SUM) test.hex
 	$(TINYGO) build -size short -o test.hex -target=pca10040            examples/mcp3008

src/examples/echo2/echo2.go

@@ -0,0 +1,31 @@
+// This is a echo console running on the os.Stdin and os.Stdout.
+// Stdin and os.Stdout are connected to machine.Serial in the baremetal target.
+//
+// Serial can be switched with the -serial option as follows
+// 1. tinygo flash -target wioterminal -serial usb examples/echo2
+// 2. tinygo flash -target wioterminal -serial uart examples/echo2
+//
+// This example will also work with standard Go.
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+)
+
+func main() {
+	fmt.Printf("Echo console enabled. Type something then press enter:\r\n")
+
+	scanner := bufio.NewScanner(os.Stdin)
+
+	for {
+		msg := ""
+		fmt.Scanf("%s\n", &msg)
+		fmt.Printf("You typed (scanf) : %s\r\n", msg)
+
+		if scanner.Scan() {
+			fmt.Printf("You typed (scanner) : %s\r\n", scanner.Text())
+		}
+	}
+}

src/os/file_other.go

@@ -38,9 +38,26 @@ func NewFile(fd uintptr, name string) *File {
 	return &File{&file{stdioFileHandle(fd), name}}
 }
 
-// Read is unsupported on this system.
+// Read reads up to len(b) bytes from machine.Serial.
+// It returns the number of bytes read and any error encountered.
 func (f stdioFileHandle) Read(b []byte) (n int, err error) {
-	return 0, ErrUnsupported
+	if len(b) == 0 {
+		return 0, nil
+	}
+
+	size := buffered()
+	for size == 0 {
+		gosched()
+		size = buffered()
+	}
+
+	if size > len(b) {
+		size = len(b)
+	}
+	for i := 0; i < size; i++ {
+		b[i] = getchar()
+	}
+	return size, nil
 }
 
 func (f stdioFileHandle) ReadAt(b []byte, off int64) (n int, err error) {
@@ -78,6 +95,15 @@ func (f stdioFileHandle) Fd() uintptr {
 //go:linkname putchar runtime.putchar
 func putchar(c byte)
 
+//go:linkname getchar runtime.getchar
+func getchar() byte
+
+//go:linkname buffered runtime.buffered
+func buffered() int
+
+//go:linkname gosched runtime.Gosched
+func gosched() int
+
 func Pipe() (r *File, w *File, err error) {
 	return nil, nil, ErrNotImplemented
 }

src/runtime/runtime_arm7tdmi.go

@@ -14,6 +14,16 @@ func putchar(c byte) {
 	// dummy, TODO
 }
 
+func getchar() byte {
+	// dummy, TODO
+	return 0
+}
+
+func buffered() int {
+	// dummy, TODO
+	return 0
+}
+
 //go:extern _sbss
 var _sbss [0]byte
 

src/runtime/runtime_atmega.go

@@ -16,6 +16,18 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+		Gosched()
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
 // Sleep for a given period. The period is defined by the WDT peripheral, and is
 // on most chips (at least) 3 bits wide, in powers of two from 16ms to 2s
 // (0=16ms, 1=32ms, 2=64ms...). Note that the WDT is not very accurate: it can

src/runtime/runtime_atsamd21.go

@@ -39,6 +39,18 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+		Gosched()
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
 func initClocks() {
 	// Set 1 Flash Wait State for 48MHz, required for 3.3V operation according to SAMD21 Datasheet
 	sam.NVMCTRL.CTRLB.SetBits(sam.NVMCTRL_CTRLB_RWS_HALF << sam.NVMCTRL_CTRLB_RWS_Pos)

src/runtime/runtime_atsamd51.go

@@ -39,6 +39,18 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+		Gosched()
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
 func initClocks() {
 	// set flash wait state
 	sam.NVMCTRL.CTRLA.SetBits(0 << sam.NVMCTRL_CTRLA_RWS_Pos)

src/runtime/runtime_attiny.go

@@ -14,6 +14,16 @@ func putchar(c byte) {
 	// UART is not supported.
 }
 
+func getchar() byte {
+	// UART is not supported.
+	return 0
+}
+
+func buffered() int {
+	// UART is not supported.
+	return 0
+}
+
 func sleepWDT(period uint8) {
 	// TODO: use the watchdog timer instead of a busy loop.
 	for i := 0x45; i != 0; i-- {

src/runtime/runtime_cortexm_qemu.go

@@ -49,6 +49,16 @@ func putchar(c byte) {
 	stdoutWrite.Set(uint8(c))
 }
 
+func getchar() byte {
+	// dummy, TODO
+	return 0
+}
+
+func buffered() int {
+	// dummy, TODO
+	return 0
+}
+
 func waitForEvents() {
 	arm.Asm("wfe")
 }

src/runtime/runtime_esp32xx.go

@@ -15,6 +15,18 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+		Gosched()
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
 // Initialize .bss: zero-initialized global variables.
 // The .data section has already been loaded by the ROM bootloader.
 func clearbss() {