From 87e48c105791187ae1bbd096ae55029de2b072a3 Mon Sep 17 00:00:00 2001
From: deadprogram <ron@hybridgroup.com>
Date: Wed, 9 Jun 2021 19:11:42 +0200
Subject: [PATCH] machine/rp2040: implement UART0/UART1, can be used on all
 rp2040 boards

Signed-off-by: deadprogram <ron@hybridgroup.com>
---
 src/machine/board_nano-rp2040.go   |   6 --
 src/machine/machine_rp2040.go      |  34 +++++++-
 src/machine/machine_rp2040_gpio.go |   3 +
 src/machine/machine_rp2040_uart.go | 133 +++++++++++++++++++++++++++++
 src/machine/uart.go                |  19 ++++-
 src/runtime/runtime_rp2040.go      |   5 ++
 6 files changed, 192 insertions(+), 8 deletions(-)
 create mode 100644 src/machine/machine_rp2040_uart.go

diff --git a/src/machine/board_nano-rp2040.go b/src/machine/board_nano-rp2040.go
index 2863f672..ca85596a 100644
--- a/src/machine/board_nano-rp2040.go
+++ b/src/machine/board_nano-rp2040.go
@@ -47,12 +47,6 @@ const (
 	LED = GPIO6
 )
 
-// UART1 pins
-const (
-	UART_TX_PIN Pin = GPIO0
-	UART_RX_PIN Pin = GPIO1
-)
-
 // I2C pins
 const (
 	SDA_PIN Pin = GPIO12
diff --git a/src/machine/machine_rp2040.go b/src/machine/machine_rp2040.go
index 7f0a71c4..f7580967 100644
--- a/src/machine/machine_rp2040.go
+++ b/src/machine/machine_rp2040.go
@@ -4,7 +4,7 @@ package machine
 
 import (
 	"device/rp"
-	_ "unsafe"
+	"runtime/interrupt"
 )
 
 const (
@@ -82,3 +82,35 @@ func machineInit() {
 func ticks() uint64 {
 	return timer.timeElapsed()
 }
+
+// UART pins
+const (
+	UART_TX_PIN  = UART0_TX_PIN
+	UART_RX_PIN  = UART0_RX_PIN
+	UART0_TX_PIN = GPIO0
+	UART0_RX_PIN = GPIO1
+	UART1_TX_PIN = GPIO8
+	UART1_RX_PIN = GPIO9
+)
+
+// UART on the RP2040
+var (
+	UART0  = &_UART0
+	_UART0 = UART{
+		Buffer: NewRingBuffer(),
+		Bus:    rp.UART0,
+	}
+
+	UART1  = &_UART1
+	_UART1 = UART{
+		Buffer: NewRingBuffer(),
+		Bus:    rp.UART1,
+	}
+)
+
+var Serial = UART0
+
+func init() {
+	UART0.Interrupt = interrupt.New(rp.IRQ_UART0_IRQ, _UART0.handleInterrupt)
+	UART1.Interrupt = interrupt.New(rp.IRQ_UART1_IRQ, _UART1.handleInterrupt)
+}
diff --git a/src/machine/machine_rp2040_gpio.go b/src/machine/machine_rp2040_gpio.go
index 62c6c335..b994988e 100644
--- a/src/machine/machine_rp2040_gpio.go
+++ b/src/machine/machine_rp2040_gpio.go
@@ -67,6 +67,7 @@ const (
 	PinInputPulldown
 	PinInputPullup
 	PinAnalog
+	PinUART
 )
 
 // set drives the pin high
@@ -152,6 +153,8 @@ func (p Pin) Configure(config PinConfig) {
 	case PinAnalog:
 		p.setFunc(fnNULL)
 		p.pulloff()
+	case PinUART:
+		p.setFunc(fnUART)
 	}
 }
 
diff --git a/src/machine/machine_rp2040_uart.go b/src/machine/machine_rp2040_uart.go
new file mode 100644
index 00000000..e2b5f733
--- /dev/null
+++ b/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)))
+}
diff --git a/src/machine/uart.go b/src/machine/uart.go
index 38046fba..701fb979 100644
--- a/src/machine/uart.go
+++ b/src/machine/uart.go
@@ -1,4 +1,4 @@
-// +build atmega esp nrf sam sifive stm32 k210 nxp
+// +build atmega esp nrf sam sifive stm32 k210 nxp rp2040
 
 package machine
 
@@ -6,6 +6,23 @@ import "errors"
 
 var errUARTBufferEmpty = errors.New("UART buffer empty")
 
+// UARTParity is the parity setting to be used for UART communication.
+type UARTParity int
+
+const (
+	// ParityNone means to not use any parity checking. This is
+	// the most common setting.
+	ParityNone UARTParity = 0
+
+	// ParityEven means to expect that the total number of 1 bits sent
+	// should be an even number.
+	ParityEven UARTParity = 1
+
+	// ParityOdd means to expect that the total number of 1 bits sent
+	// should be an odd number.
+	ParityOdd UARTParity = 2
+)
+
 type UARTConfig struct {
 	BaudRate uint32
 	TX       Pin
diff --git a/src/runtime/runtime_rp2040.go b/src/runtime/runtime_rp2040.go
index 162f18f1..7d3c9310 100644
--- a/src/runtime/runtime_rp2040.go
+++ b/src/runtime/runtime_rp2040.go
@@ -4,6 +4,8 @@ package runtime
 
 import (
 	"device/arm"
+
+	"machine"
 )
 
 // machineTicks is provided by package machine.
@@ -39,6 +41,7 @@ func waitForEvents() {
 }
 
 func putchar(c byte) {
+	machine.Serial.WriteByte(c)
 }
 
 // machineInit is provided by package machine.
@@ -46,6 +49,8 @@ func machineInit()
 
 func init() {
 	machineInit()
+
+	machine.Serial.Configure(machine.UARTConfig{})
 }
 
 func postinit() {}