machine/rp2040: implement UART0/UART1, can be used on all rp2040 boards

Signed-off-by: deadprogram <ron@hybridgroup.com>

src/machine/machine_rp2040_uart.go

@@ -0,0 +1,133 @@
+// +build rp2040
+
+package machine
+
+import (
+	"device/rp"
+	"runtime/interrupt"
+)
+
+// UART on the RP2040.
+type UART struct {
+	Buffer    *RingBuffer
+	Bus       *rp.UART0_Type
+	Interrupt interrupt.Interrupt
+}
+
+// Configure the UART.
+func (uart *UART) Configure(config UARTConfig) error {
+	initUART(uart)
+
+	// Default baud rate to 115200.
+	if config.BaudRate == 0 {
+		config.BaudRate = 115200
+	}
+
+	// Use default pins if pins are not set.
+	if config.TX == 0 && config.RX == 0 {
+		// use default pins
+		config.TX = UART_TX_PIN
+		config.RX = UART_RX_PIN
+	}
+
+	uart.SetBaudRate(config.BaudRate)
+
+	// default to 8-1-N
+	uart.SetFormat(8, 1, ParityNone)
+
+	// Enable the UART, both TX and RX
+	uart.Bus.UARTCR.SetBits(rp.UART0_UARTCR_UARTEN |
+		rp.UART0_UARTCR_RXE |
+		rp.UART0_UARTCR_TXE)
+
+	// set GPIO mux to UART for the pins
+	config.TX.Configure(PinConfig{Mode: PinUART})
+	config.RX.Configure(PinConfig{Mode: PinUART})
+
+	// Enable RX IRQ.
+	uart.Interrupt.SetPriority(0x80)
+	uart.Interrupt.Enable()
+
+	// setup interrupt on receive
+	uart.Bus.UARTIMSC.Set(rp.UART0_UARTIMSC_RXIM)
+
+	return nil
+}
+
+// SetBaudRate sets the baudrate to be used for the UART.
+func (uart *UART) SetBaudRate(br uint32) {
+	div := 8 * 125 * MHz / br
+
+	ibrd := div >> 7
+	var fbrd uint32
+
+	switch {
+	case ibrd == 0:
+		ibrd = 1
+		fbrd = 0
+	case ibrd >= 65535:
+		ibrd = 65535
+		fbrd = 0
+	default:
+		fbrd = ((div & 0x7f) + 1) / 2
+	}
+
+	// set PL011 baud divisor registers
+	uart.Bus.UARTIBRD.Set(ibrd)
+	uart.Bus.UARTFBRD.Set(fbrd)
+
+	// PL011 needs a (dummy) line control register write.
+	// See https://github.com/raspberrypi/pico-sdk/blob/master/src/rp2_common/hardware_uart/uart.c#L93-L95
+	uart.Bus.UARTLCR_H.SetBits(0)
+}
+
+// WriteByte writes a byte of data to the UART.
+func (uart *UART) WriteByte(c byte) error {
+	// wait until buffer is not full
+	for uart.Bus.UARTFR.HasBits(rp.UART0_UARTFR_TXFF) {
+	}
+
+	// write data
+	uart.Bus.UARTDR.Set(uint32(c))
+	return nil
+}
+
+// SetFormat for number of data bits, stop bits, and parity for the UART.
+func (uart *UART) SetFormat(databits, stopbits uint8, parity UARTParity) error {
+	var pen, pev uint8
+	if parity != ParityNone {
+		pen = rp.UART0_UARTLCR_H_PEN
+	}
+	if parity == ParityEven {
+		pev = rp.UART0_UARTLCR_H_EPS
+	}
+	uart.Bus.UARTLCR_H.SetBits(uint32((databits-5)<<rp.UART0_UARTLCR_H_WLEN_Pos |
+		(stopbits-1)<<rp.UART0_UARTLCR_H_STP2_Pos |
+		pen | pev))
+
+	return nil
+}
+
+func initUART(uart *UART) {
+	var resetVal uint32
+	switch {
+	case uart.Bus == rp.UART0:
+		resetVal = rp.RESETS_RESET_UART0
+	case uart.Bus == rp.UART1:
+		resetVal = rp.RESETS_RESET_UART1
+	}
+
+	// reset UART
+	rp.RESETS.RESET.SetBits(resetVal)
+	rp.RESETS.RESET.ClearBits(resetVal)
+	for !rp.RESETS.RESET_DONE.HasBits(resetVal) {
+	}
+}
+
+// handleInterrupt should be called from the appropriate interrupt handler for
+// this UART instance.
+func (uart *UART) handleInterrupt(interrupt.Interrupt) {
+	for uart.Bus.UARTFR.HasBits(rp.UART0_UARTFR_RXFE) {
+	}
+	uart.Receive(byte((uart.Bus.UARTDR.Get() & 0xFF)))
+}