machine.UART refactor (#3832)

* add gosched calls to UART

* add UART.flush() stubs for all supported architectures

* add comment un uart.go on flush functionality

* uart.writeByte as base of UART usage

* fix NXP having duplicate WriteByte

* fix writeByte not returning error on some platforms

* add flush method for fe310 device

* check for error in WriteByte call to writeByte

Author: soypat

src/machine/machine_atmega.go

@@ -97,7 +97,7 @@ func (i2c *I2C) stop() {
 }
 
 // writeByte writes a single byte to the I2C bus.
-func (i2c *I2C) writeByte(data byte) {
+func (i2c *I2C) writeByte(data byte) error {
 	// Write data to register.
 	avr.TWDR.Set(data)
 
@@ -107,6 +107,7 @@ func (i2c *I2C) writeByte(data byte) {
 	// Wait till data is transmitted.
 	for !avr.TWCR.HasBits(avr.TWCR_TWINT) {
 	}
+	return nil
 }
 
 // readByte reads a single byte from the I2C bus.
@@ -190,14 +191,16 @@ func (uart *UART) handleInterrupt(intr interrupt.Interrupt) {
 }
 
 // WriteByte writes a byte of data to the UART.
-func (uart *UART) WriteByte(c byte) error {
+func (uart *UART) writeByte(c byte) error {
 	// Wait until UART buffer is not busy.
 	for !uart.statusRegA.HasBits(avr.UCSR0A_UDRE0) {
 	}
 	uart.dataReg.Set(c) // send char
 	return nil
 }
 
+func (uart *UART) flush() {}
+
 // SPIConfig is used to store config info for SPI.
 type SPIConfig struct {
 	Frequency uint32

src/machine/machine_atsamd21.go

@@ -626,14 +626,16 @@ func (uart *UART) SetBaudRate(br uint32) {
 }
 
 // WriteByte writes a byte of data to the UART.
-func (uart *UART) WriteByte(c byte) error {
+func (uart *UART) writeByte(c byte) error {
 	// wait until ready to receive
 	for !uart.Bus.INTFLAG.HasBits(sam.SERCOM_USART_INTFLAG_DRE) {
 	}
 	uart.Bus.DATA.Set(uint16(c))
 	return nil
 }
 
+func (uart *UART) flush() {}
+
 // handleInterrupt should be called from the appropriate interrupt handler for
 // this UART instance.
 func (uart *UART) handleInterrupt(interrupt.Interrupt) {

src/machine/machine_atsamd51.go

@@ -1114,14 +1114,16 @@ func (uart *UART) SetBaudRate(br uint32) {
 }
 
 // WriteByte writes a byte of data to the UART.
-func (uart *UART) WriteByte(c byte) error {
+func (uart *UART) writeByte(c byte) error {
 	// wait until ready to receive
 	for !uart.Bus.INTFLAG.HasBits(sam.SERCOM_USART_INT_INTFLAG_DRE) {
 	}
 	uart.Bus.DATA.Set(uint32(c))
 	return nil
 }
 
+func (uart *UART) flush() {}
+
 func (uart *UART) handleInterrupt(interrupt.Interrupt) {
 	// should reset IRQ
 	uart.Receive(byte((uart.Bus.DATA.Get() & 0xFF)))

src/machine/machine_esp32.go

@@ -314,7 +314,7 @@ func (uart *UART) Configure(config UARTConfig) {
 	uart.Bus.CLKDIV.Set(peripheralClock / config.BaudRate)
 }
 
-func (uart *UART) WriteByte(b byte) error {
+func (uart *UART) writeByte(b byte) error {
 	for (uart.Bus.STATUS.Get()>>16)&0xff >= 128 {
 		// Read UART_TXFIFO_CNT from the status register, which indicates how
 		// many bytes there are in the transmit buffer. Wait until there are
@@ -324,6 +324,8 @@ func (uart *UART) WriteByte(b byte) error {
 	return nil
 }
 
+func (uart *UART) flush() {}
+
 // Serial Peripheral Interface on the ESP32.
 type SPI struct {
 	Bus *esp.SPI_Type

src/machine/machine_esp32c3.go

@@ -493,7 +493,7 @@ func (uart *UART) enableReceiver() {
 	uart.Bus.SetINT_ENA_RXFIFO_OVF_INT_ENA(1)
 }
 
-func (uart *UART) WriteByte(b byte) error {
+func (uart *UART) writeByte(b byte) error {
 	for (uart.Bus.STATUS.Get()&esp.UART_STATUS_TXFIFO_CNT_Msk)>>esp.UART_STATUS_TXFIFO_CNT_Pos >= 128 {
 		// Read UART_TXFIFO_CNT from the status register, which indicates how
 		// many bytes there are in the transmit buffer. Wait until there are
@@ -502,3 +502,5 @@ func (uart *UART) WriteByte(b byte) error {
 	uart.Bus.FIFO.Set(uint32(b))
 	return nil
 }
+
+func (uart *UART) flush() {}

src/machine/machine_esp8266.go

@@ -181,12 +181,14 @@ func (uart *UART) Configure(config UARTConfig) {
 	esp.UART0.UART_CLKDIV.Set(CPUFrequency() / config.BaudRate)
 }
 
-// WriteByte writes a single byte to the output buffer. Note that the hardware
+// writeByte writes a single byte to the output buffer. Note that the hardware
 // includes a buffer of 128 bytes which will be used first.
-func (uart *UART) WriteByte(c byte) error {
+func (uart *UART) writeByte(c byte) error {
 	for (esp.UART0.UART_STATUS.Get()>>16)&0xff >= 128 {
 		// Wait until the TX buffer has room.
 	}
 	esp.UART0.UART_FIFO.Set(uint32(c))
 	return nil
 }
+
+func (uart *UART) flush() {}

src/machine/machine_fe310.go

@@ -111,13 +111,16 @@ func (uart *UART) handleInterrupt(interrupt.Interrupt) {
 	uart.Receive(c)
 }
 
-func (uart *UART) WriteByte(c byte) {
+func (uart *UART) writeByte(c byte) error {
 	for sifive.UART0.TXDATA.Get()&sifive.UART_TXDATA_FULL != 0 {
 	}
 
 	sifive.UART0.TXDATA.Set(uint32(c))
+	return nil
 }
 
+func (uart *UART) flush() {}
+
 // SPI on the FE310. The normal SPI0 is actually a quad-SPI meant for flash, so it is best
 // to use SPI1 or SPI2 port for most applications.
 type SPI struct {

src/machine/machine_k210.go

@@ -392,13 +392,16 @@ func (uart *UART) handleInterrupt(interrupt.Interrupt) {
 	uart.Receive(c)
 }
 
-func (uart *UART) WriteByte(c byte) {
+func (uart *UART) writeByte(c byte) error {
 	for uart.Bus.TXDATA.Get()&kendryte.UARTHS_TXDATA_FULL != 0 {
 	}
 
 	uart.Bus.TXDATA.Set(uint32(c))
+	return nil
 }
 
+func (uart *UART) flush() {}
+
 type SPI struct {
 	Bus *kendryte.SPI_Type
 }

src/machine/machine_mimxrt1062_uart.go

@@ -173,14 +173,16 @@ func (uart *UART) Sync() error {
 }
 
 // WriteByte writes a single byte of data to the UART interface.
-func (uart *UART) WriteByte(c byte) error {
+func (uart *UART) writeByte(c byte) error {
 	uart.startTransmitting()
 	for !uart.txBuffer.Put(c) {
 	}
 	uart.Bus.CTRL.SetBits(nxp.LPUART_CTRL_TIE)
 	return nil
 }
 
+func (uart *UART) flush() {}
+
 // getBaudRateDivisor finds the greatest over-sampling factor (4..32) and
 // corresponding baud rate divisor (1..8191) that best partition a given baud
 // rate into equal intervals.

src/machine/machine_nrf.go

@@ -186,14 +186,16 @@ func (uart *UART) SetBaudRate(br uint32) {
 }
 
 // WriteByte writes a byte of data to the UART.
-func (uart *UART) WriteByte(c byte) error {
+func (uart *UART) writeByte(c byte) error {
 	nrf.UART0.EVENTS_TXDRDY.Set(0)
 	nrf.UART0.TXD.Set(uint32(c))
 	for nrf.UART0.EVENTS_TXDRDY.Get() == 0 {
 	}
 	return nil
 }
 
+func (uart *UART) flush() {}
+
 func (uart *UART) handleInterrupt(interrupt.Interrupt) {
 	if nrf.UART0.EVENTS_RXDRDY.Get() != 0 {
 		uart.Receive(byte(nrf.UART0.RXD.Get()))