Update

src/os/file_other.go

@@ -4,7 +4,6 @@
 package os
 
 import (
-	"machine"
 	_ "unsafe"
 )
 
@@ -42,7 +41,18 @@ func NewFile(fd uintptr, name string) *File {
 // 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 machine.Serial.Read(b)
+	size := 0
+	for size == 0 {
+		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) {
@@ -76,6 +86,12 @@ func (f stdioFileHandle) Seek(offset int64, whence int) (int64, error) {
 //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
+
 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 +16,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	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

@@ -36,6 +36,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	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

@@ -36,6 +36,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	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 +15,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	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() {

src/runtime/runtime_esp8266.go

@@ -18,6 +18,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
 // Write to the internal control bus (using I2C?).
 // Signature found here:
 // https://github.com/espressif/ESP8266_RTOS_SDK/blob/14171de0/components/esp8266/include/esp8266/rom_functions.h#L54

src/runtime/runtime_fe310.go

@@ -99,6 +99,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
 var timerWakeup volatile.Register8
 
 func ticks() timeUnit {

src/runtime/runtime_k210.go

@@ -111,6 +111,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
 var timerWakeup volatile.Register8
 
 func ticks() timeUnit {

src/runtime/runtime_mimxrt1062.go

@@ -126,6 +126,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.UART1.Buffered() == 0 {
+	}
+	v, _ := machine.UART1.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.UART1.Buffered()
+}
+
 func exit(code int) {
 	abort()
 }

src/runtime/runtime_nrf.go

@@ -66,6 +66,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
 func sleepTicks(d timeUnit) {
 	for d != 0 {
 		ticks := uint32(d) & 0x7fffff // 23 bits (to be on the safe side)

src/runtime/runtime_nxpmk66f18.go

@@ -231,6 +231,16 @@ func putchar(c byte) {
 	machine.PutcharUART(machine.UART0, c)
 }
 
+func getchar() byte {
+	// dummy, TODO
+	return 0
+}
+
+func buffered() int {
+	// dummy, TODO
+	return 0
+}
+
 func exit(code int) {
 	abort()
 }

src/runtime/runtime_rp2040.go

@@ -45,6 +45,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
 // machineInit is provided by package machine.
 func machineInit()
 

src/runtime/runtime_stm32f103.go

@@ -20,6 +20,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
 // initCLK sets clock to 72MHz using HSE 8MHz crystal w/ PLL X 9 (8MHz x 9 = 72MHz).
 func initCLK() {
 	stm32.FLASH.ACR.SetBits(stm32.FLASH_ACR_LATENCY_WS2)                          // Two wait states, per datasheet

src/runtime/runtime_stm32f4.go

@@ -21,6 +21,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
 func initCLK() {
 	// Reset clock registers
 	// Set HSION

src/runtime/runtime_stm32f405.go

@@ -163,3 +163,14 @@ func initCOM() {
 func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
+
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}

src/runtime/runtime_stm32f7x2.go

@@ -38,6 +38,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
 func initCLK() {
 	// PWR_CLK_ENABLE
 	stm32.RCC.APB1ENR.SetBits(stm32.RCC_APB1ENR_PWREN)

src/runtime/runtime_stm32l0.go

@@ -16,6 +16,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
 func initCLK() {
 	// Set Power Regulator to enable max performance (1.8V)
 	stm32.PWR.CR.ReplaceBits(1<<stm32.PWR_CR_VOS_Pos, stm32.PWR_CR_VOS_Msk, 0)

src/runtime/runtime_stm32l4.go

@@ -47,6 +47,17 @@ func putchar(c byte) {
 	machine.Serial.WriteByte(c)
 }
 
+func getchar() byte {
+	for machine.Serial.Buffered() == 0 {
+	}
+	v, _ := machine.Serial.ReadByte()
+	return v
+}
+
+func buffered() int {
+	return machine.Serial.Buffered()
+}
+
 func initCLK() {
 	// PWR_CLK_ENABLE
 	stm32.RCC.APB1ENR1.SetBits(stm32.RCC_APB1ENR1_PWREN)