sam: simplify definition of SERCOM UART peripherals

Instead of defining them separately for each board, define them once in
the chip definition and later simply use &sercomUART1 etc. to refer to
them. This is simpler and less error-prone.

I found two bugs while working on this:

  - The P1AM-100 board mixed SERCOM 5 and SERCOM 3. It looks like SERCOM
    5 was intended, based on the used pins.
  - The Adafruit Matrix Portal appears to have configured the wrong
    interrupt.

Unfortunately, I can't test these fixes. However, they make it clear
that such a change is important to avoid bugs.

I tested this commit on the PyBadge and the Circuit Playground Express.

src/machine/board_arduino_mkrwifi1010.go

@@ -8,7 +8,6 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
 // used to reset into bootloader
@@ -98,18 +97,7 @@ const (
 )
 
 // UART on the Arduino MKR WiFi 1010.
-var (
+var UART1 = &sercomUSART5
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM5_USART,
-		SERCOM: 5,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM5, _UART1.handleInterrupt)
-}
 
 // I2C on the Arduino MKR WiFi 1010.
 var (

src/machine/board_arduino_nano33.go

@@ -58,6 +58,12 @@ const (
 	UART_RX_PIN Pin = PA23
 )
 
+// UART1 on the Arduino Nano 33 connects to the onboard NINA-W102 WiFi chip.
+var UART1 = &sercomUSART3
+
+// UART2 on the Arduino Nano 33 connects to the normal TX/RX pins.
+var UART2 = &sercomUSART5
+
 // I2C pins
 const (
 	SDA_PIN Pin = A4 // SDA: SERCOM4/PAD[1]

src/machine/board_arduino_nano33_baremetal.go

@@ -4,34 +4,8 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
-// UART1 on the Arduino Nano 33 connects to the onboard NINA-W102 WiFi chip.
-var (
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM3_USART,
-		SERCOM: 3,
-	}
-)
-
-// UART2 on the Arduino Nano 33 connects to the normal TX/RX pins.
-var (
-	UART2  = &_UART2
-	_UART2 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM5_USART,
-		SERCOM: 5,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM3, _UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM5, _UART2.handleInterrupt)
-}
-
 // I2C on the Arduino Nano 33.
 var (
 	I2C0 = &I2C{

src/machine/board_atsame54-xpro.go

@@ -4,7 +4,6 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
 // Definition for compatibility, but not used
@@ -240,45 +239,18 @@ var (
 // UART on the SAM E54 Xplained Pro
 var (
 	// Extension Header EXT1
-	UART1  = &_UART1
+	UART1 = &sercomUSART0
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM0_USART_INT,
-		SERCOM: 0,
-	}
 
 	// Extension Header EXT2
-	UART2  = &_UART2
+	UART2 = &sercomUSART5
-	_UART2 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM5_USART_INT,
-		SERCOM: 5,
-	}
 
 	// Extension Header EXT3
-	UART3  = &_UART3
+	UART3 = &sercomUSART1
-	_UART3 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM1_USART_INT,
-		SERCOM: 1,
-	}
 
 	// EDBG Virtual COM Port
-	UART4  = &_UART4
+	UART4 = &sercomUSART2
-	_UART4 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM2_USART_INT,
-		SERCOM: 2,
-	}
 )
 
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, _UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, _UART2.handleInterrupt)
-	UART3.Interrupt = interrupt.New(sam.IRQ_SERCOM1_2, _UART3.handleInterrupt)
-	UART4.Interrupt = interrupt.New(sam.IRQ_SERCOM2_2, _UART4.handleInterrupt)
-}
-
 // I2C on the SAM E54 Xplained Pro
 var (
 	// Extension Header EXT1

src/machine/board_circuitplay_express.go

@@ -67,6 +67,13 @@ const (
 	UART_RX_PIN = PB09 // PORTB
 )
 
+// UART1 on the Circuit Playground Express.
+var (
+	UART1 = &sercomUSART4
+
+	DefaultUART = UART1
+)
+
 // I2C pins
 const (
 	SDA_PIN = PB02 // I2C0 external

src/machine/board_circuitplay_express_baremetal.go

@@ -4,23 +4,8 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
-// UART1 on the Circuit Playground Express.
-var (
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM4_USART,
-		SERCOM: 4,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM4, _UART1.handleInterrupt)
-}
-
 // I2C on the Circuit Playground Express.
 var (
 	// external device
@@ -47,7 +32,3 @@ var (
 var (
 	I2S0 = I2S{Bus: sam.I2S}
 )
-
-var (
-	DefaultUART = UART1
-)

src/machine/board_feather-m0.go

@@ -4,7 +4,6 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
 // used to reset into bootloader
@@ -55,18 +54,7 @@ const (
 )
 
 // UART1 on the Feather M0.
-var (
+var UART1 = &sercomUSART1
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM1_USART,
-		SERCOM: 1,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM1, _UART1.handleInterrupt)
-}
 
 // I2C pins
 const (

src/machine/board_feather-m4-can.go

@@ -4,7 +4,6 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
 // used to reset into bootloader
@@ -104,25 +103,12 @@ var (
 )
 
 var (
-	UART1  = &_UART1
+	UART1 = &sercomUSART5
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM5_USART_INT,
-		SERCOM: 5,
-	}
 
-	UART2  = &_UART2
+	UART2 = &sercomUSART0
-	_UART2 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM0_USART_INT,
-		SERCOM: 0,
-	}
 )
 
 func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, _UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, _UART2.handleInterrupt)
-
 	// turn on neopixel
 	D7.Configure(PinConfig{Mode: PinOutput})
 	D7.High()

src/machine/board_feather-m4.go

@@ -56,6 +56,13 @@ const (
 	UART2_RX_PIN = A5
 )
 
+var (
+	UART1 = &sercomUSART5
+	UART2 = &sercomUSART0
+
+	DefaultUART = UART1
+)
+
 // I2C pins
 const (
 	SDA_PIN = D22 // SDA: SERCOM2/PAD[0]

src/machine/board_feather-m4_baremetal.go

@@ -4,30 +4,8 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
-var (
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM5_USART_INT,
-		SERCOM: 5,
-	}
-
-	UART2  = &_UART2
-	_UART2 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM0_USART_INT,
-		SERCOM: 0,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, _UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, _UART2.handleInterrupt)
-}
-
 // I2C on the Feather M4.
 var (
 	I2C0 = &I2C{
@@ -43,7 +21,3 @@ var (
 		SERCOM: 1,
 	}
 )
-
-var (
-	DefaultUART = UART1
-)

src/machine/board_grandcentral-m4.go

@@ -160,6 +160,16 @@ const (
 	UART_TX_PIN = UART1_TX_PIN //
 )
 
+// UART on the Grand Central M4
+var (
+	UART1 = &sercomUSART0
+	UART2 = &sercomUSART4
+	UART3 = &sercomUSART1
+	UART4 = &sercomUSART5
+
+	DefaultUART = UART1
+)
+
 // SPI pins
 const (
 	SPI0_SCK_PIN = D66 // (PD09), also on D52

src/machine/board_grandcentral-m4_baremetal.go

@@ -4,42 +4,6 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, _UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM4_2, _UART2.handleInterrupt)
-	UART3.Interrupt = interrupt.New(sam.IRQ_SERCOM1_2, _UART3.handleInterrupt)
-	UART4.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, _UART4.handleInterrupt)
-}
-
-// UART on the Grand Central M4
-var (
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM0_USART_INT,
-		SERCOM: 0,
-	}
-	UART2  = &_UART2
-	_UART2 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM4_USART_INT,
-		SERCOM: 4,
-	}
-	UART3  = &_UART3
-	_UART3 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM1_USART_INT,
-		SERCOM: 1,
-	}
-	UART4  = &_UART4
-	_UART4 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM5_USART_INT,
-		SERCOM: 5,
-	}
 )
 
 // I2C on the Grand Central M4
@@ -65,7 +29,3 @@ var (
 		SERCOM: 2,
 	}
 )
-
-var (
-	DefaultUART = UART1
-)

src/machine/board_itsybitsy-m0.go

@@ -4,7 +4,6 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
 // used to reset into bootloader
@@ -56,18 +55,9 @@ const (
 
 // UART1 on the ItsyBitsy M0.
 var (
-	UART1  = &_UART1
+	UART1 = &sercomUSART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM1_USART,
-		SERCOM: 1,
-	}
 )
 
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM1, _UART1.handleInterrupt)
-}
-
 // I2C pins
 const (
 	SDA_PIN = PA22 // SDA: SERCOM3/PAD[0]

src/machine/board_itsybitsy-m4.go

@@ -54,6 +54,13 @@ const (
 	UART2_RX_PIN = D2
 )
 
+var (
+	UART1 = &sercomUSART3
+	UART2 = &sercomUSART0
+
+	DefaultUART = UART1
+)
+
 // I2C pins
 const (
 	SDA_PIN = PA12 // SDA: SERCOM2/PAD[0]

src/machine/board_itsybitsy-m4_baremetal.go

@@ -4,30 +4,8 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
-var (
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM3_USART_INT,
-		SERCOM: 3,
-	}
-
-	UART2  = &_UART2
-	_UART2 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM0_USART_INT,
-		SERCOM: 0,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM3_2, _UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, _UART2.handleInterrupt)
-}
-
 // I2C on the ItsyBitsy M4.
 var (
 	I2C0 = &I2C{
@@ -43,7 +21,3 @@ var (
 		SERCOM: 1,
 	}
 )
-
-var (
-	DefaultUART = UART1
-)

src/machine/board_matrixportal-m4.go

@@ -96,6 +96,14 @@ const (
 	UART_TX_PIN = UART1_TX_PIN
 )
 
+// UART on the MatrixPortal M4
+var (
+	UART1 = &sercomUSART1
+	UART2 = &sercomUSART4
+
+	DefaultUART = UART1
+)
+
 // SPI pins
 const (
 	SPI0_SCK_PIN = D34 // SERCOM3[1] (ESP32 SCK)

src/machine/board_matrixportal-m4_baremetal.go

@@ -4,31 +4,8 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
-// UART on the MatrixPortal M4
-var (
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM1_USART_INT,
-		SERCOM: 1,
-	}
-
-	UART2  = &_UART2
-	_UART2 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM4_USART_INT,
-		SERCOM: 4,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM1_1, _UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM4_1, _UART2.handleInterrupt)
-}
-
 // I2C on the MatrixPortal M4
 var (
 	I2C0 = &I2C{
@@ -50,7 +27,3 @@ var (
 		SERCOM: 0,
 	}
 )
-
-var (
-	DefaultUART = UART1
-)

src/machine/board_metro-m4-airlift.go

@@ -57,6 +57,13 @@ const (
 	UART2_RX_PIN = PA07
 )
 
+var (
+	UART1 = &sercomUSART3
+	UART2 = &sercomUSART0
+
+	DefaultUART = UART1
+)
+
 const (
 	NINA_CS     = PA15
 	NINA_ACK    = PB04

src/machine/board_metro-m4-airlift_baremetal.go

@@ -4,30 +4,8 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
-var (
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM3_USART_INT,
-		SERCOM: 3,
-	}
-
-	UART2  = &_UART2
-	_UART2 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM0_USART_INT,
-		SERCOM: 0,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM3_2, _UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, _UART2.handleInterrupt)
-}
-
 // I2C on the Metro M4.
 var (
 	I2C0 = &I2C{
@@ -52,7 +30,3 @@ var (
 		SERCOM: 1,
 	}
 )
-
-var (
-	DefaultUART = UART1
-)

src/machine/board_p1am-100.go

@@ -79,6 +79,9 @@ const (
 	UART_TX_PIN Pin = PB22 // TX: SERCOM5/PAD[2]
 )
 
+// UART1 on the P1AM-100 connects to the normal TX/RX pins.
+var UART1 = &sercomUSART5
+
 // I2C pins
 const (
 	SDA_PIN Pin = PA08 // SDA:  SERCOM0/PAD[0]

src/machine/board_p1am-100_baremetal.go

@@ -4,23 +4,8 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
-// UART1 on the P1AM-100 connects to the normal TX/RX pins.
-var (
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM3_USART,
-		SERCOM: 5,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM5, _UART1.handleInterrupt)
-}
-
 // I2C on the P1AM-100.
 var (
 	I2C0 = &I2C{

src/machine/board_pybadge.go

@@ -84,6 +84,13 @@ const (
 	UART2_RX_PIN = A5
 )
 
+var (
+	UART1 = &sercomUSART5
+	UART2 = &sercomUSART0
+
+	DefaultUART = UART1
+)
+
 // I2C pins
 const (
 	SDA_PIN = PA12 // SDA: SERCOM2/PAD[0]

src/machine/board_pybadge_baremetal.go

@@ -4,30 +4,8 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
-var (
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM5_USART_INT,
-		SERCOM: 5,
-	}
-
-	UART2  = &_UART2
-	_UART2 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM0_USART_INT,
-		SERCOM: 0,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, _UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, _UART2.handleInterrupt)
-}
-
 // I2C on the ItsyBitsy M4.
 var (
 	I2C0 = &I2C{
@@ -51,7 +29,3 @@ var (
 		SERCOM: 4,
 	}
 )
-
-var (
-	DefaultUART = UART1
-)

src/machine/board_pyportal.go

@@ -107,6 +107,12 @@ const (
 	UART_RX_PIN = D0
 )
 
+var (
+	UART1 = &sercomUSART4
+
+	DefaultUART = UART1
+)
+
 // I2C pins
 const (
 	SDA_PIN = PB02 // SDA: SERCOM2/PAD[0]

src/machine/board_pyportal_baremetal.go

@@ -4,22 +4,8 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
-var (
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM4_USART_INT,
-		SERCOM: 4,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM4_2, _UART1.handleInterrupt)
-}
-
 // I2C on the PyPortal.
 var (
 	I2C0 = &I2C{
@@ -36,7 +22,3 @@ var (
 	}
 	NINA_SPI = SPI0
 )
-
-var (
-	DefaultUART = UART1
-)

src/machine/board_qtpy.go

@@ -4,7 +4,6 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
 // used to reset into bootloader
@@ -60,18 +59,7 @@ const (
 )
 
 // UART1 on the QT Py M0.
-var (
+var UART1 = &sercomUSART0
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM0_USART,
-		SERCOM: 0,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM0, _UART1.handleInterrupt)
-}
 
 // SPI pins
 const (

src/machine/board_trinket.go

@@ -4,7 +4,6 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
 // used to reset into bootloader
@@ -46,18 +45,7 @@ const (
 )
 
 // UART1 on the Trinket M0.
-var (
+var UART1 = &sercomUSART0
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM0_USART,
-		SERCOM: 0,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM0, _UART1.handleInterrupt)
-}
 
 // SPI pins
 const (

src/machine/board_wioterminal.go

@@ -343,6 +343,13 @@ const (
 	UART2_RX_PIN = PIN_SERIAL2_RX
 )
 
+var (
+	UART1 = &sercomUSART2
+
+	// RTL8720D
+	UART2 = &sercomUSART1
+)
+
 // I2C pins
 const (
 	SDA0_PIN = PIN_WIRE_SDA // SDA: SERCOM3/PAD[0]

src/machine/board_wioterminal_baremetal.go

@@ -4,31 +4,8 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
-var (
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM2_USART_INT,
-		SERCOM: 2,
-	}
-
-	// RTL8720D
-	UART2  = &_UART2
-	_UART2 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM1_USART_INT,
-		SERCOM: 1,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM2_2, _UART1.handleInterrupt)
-	UART2.Interrupt = interrupt.New(sam.IRQ_SERCOM1_2, _UART2.handleInterrupt)
-}
-
 // I2C on the Wio Terminal
 var (
 	I2C0 = &I2C{

src/machine/board_xiao.go

@@ -4,7 +4,6 @@ package machine
 
 import (
 	"device/sam"
-	"runtime/interrupt"
 )
 
 // used to reset into bootloader
@@ -61,18 +60,7 @@ const (
 )
 
 // UART1 on the Xiao
-var (
+var UART1 = &sercomUSART4
-	UART1  = &_UART1
-	_UART1 = UART{
-		Buffer: NewRingBuffer(),
-		Bus:    sam.SERCOM4_USART,
-		SERCOM: 4,
-	}
-)
-
-func init() {
-	UART1.Interrupt = interrupt.New(sam.IRQ_SERCOM4, _UART1.handleInterrupt)
-}
 
 // I2C pins
 const (

src/machine/machine_atsamd21.go

@@ -504,10 +504,6 @@ type UART struct {
 	Interrupt interrupt.Interrupt
 }
 
-var (
-	USB = &USBCDC{Buffer: NewRingBuffer()}
-)
-
 const (
 	sampleRate16X = 16
 	lsbFirst      = 1
@@ -1743,6 +1739,10 @@ type USBCDC struct {
 	sent              bool
 }
 
+var (
+	USB = &USBCDC{Buffer: NewRingBuffer()}
+)
+
 const (
 	usbcdcTxSizeMask          uint8 = 0x3F
 	usbcdcTxBankMask          uint8 = ^usbcdcTxSizeMask

src/machine/machine_atsamd21e18.go

@@ -9,8 +9,23 @@ package machine
 
 import (
 	"device/sam"
+	"runtime/interrupt"
 )
 
+var (
+	sercomUSART0 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM0_USART, SERCOM: 0}
+	sercomUSART1 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM1_USART, SERCOM: 1}
+	sercomUSART2 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM2_USART, SERCOM: 2}
+	sercomUSART3 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM3_USART, SERCOM: 3}
+)
+
+func init() {
+	sercomUSART0.Interrupt = interrupt.New(sam.IRQ_SERCOM0, sercomUSART0.handleInterrupt)
+	sercomUSART1.Interrupt = interrupt.New(sam.IRQ_SERCOM1, sercomUSART1.handleInterrupt)
+	sercomUSART2.Interrupt = interrupt.New(sam.IRQ_SERCOM2, sercomUSART2.handleInterrupt)
+	sercomUSART3.Interrupt = interrupt.New(sam.IRQ_SERCOM3, sercomUSART3.handleInterrupt)
+}
+
 // Return the register and mask to enable a given GPIO pin. This can be used to
 // implement bit-banged drivers.
 func (p Pin) PortMaskSet() (*uint32, uint32) {

src/machine/machine_atsamd21g18.go

@@ -9,8 +9,27 @@ package machine
 
 import (
 	"device/sam"
+	"runtime/interrupt"
 )
 
+var (
+	sercomUSART0 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM0_USART, SERCOM: 0}
+	sercomUSART1 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM1_USART, SERCOM: 1}
+	sercomUSART2 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM2_USART, SERCOM: 2}
+	sercomUSART3 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM3_USART, SERCOM: 3}
+	sercomUSART4 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM4_USART, SERCOM: 4}
+	sercomUSART5 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM5_USART, SERCOM: 5}
+)
+
+func init() {
+	sercomUSART0.Interrupt = interrupt.New(sam.IRQ_SERCOM0, sercomUSART0.handleInterrupt)
+	sercomUSART1.Interrupt = interrupt.New(sam.IRQ_SERCOM1, sercomUSART1.handleInterrupt)
+	sercomUSART2.Interrupt = interrupt.New(sam.IRQ_SERCOM2, sercomUSART2.handleInterrupt)
+	sercomUSART3.Interrupt = interrupt.New(sam.IRQ_SERCOM3, sercomUSART3.handleInterrupt)
+	sercomUSART4.Interrupt = interrupt.New(sam.IRQ_SERCOM4, sercomUSART4.handleInterrupt)
+	sercomUSART5.Interrupt = interrupt.New(sam.IRQ_SERCOM5, sercomUSART5.handleInterrupt)
+}
+
 // Return the register and mask to enable a given GPIO pin. This can be used to
 // implement bit-banged drivers.
 func (p Pin) PortMaskSet() (*uint32, uint32) {

src/machine/machine_atsamd51.go

@@ -951,10 +951,23 @@ type UART struct {
 }
 
 var (
-	// USB is a USB CDC interface.
+	sercomUSART0 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM0_USART_INT, SERCOM: 0}
-	USB = &USBCDC{Buffer: NewRingBuffer()}
+	sercomUSART1 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM1_USART_INT, SERCOM: 1}
+	sercomUSART2 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM2_USART_INT, SERCOM: 2}
+	sercomUSART3 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM3_USART_INT, SERCOM: 3}
+	sercomUSART4 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM4_USART_INT, SERCOM: 4}
+	sercomUSART5 = UART{Buffer: NewRingBuffer(), Bus: sam.SERCOM5_USART_INT, SERCOM: 5}
 )
 
+func init() {
+	sercomUSART0.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, sercomUSART0.handleInterrupt)
+	sercomUSART1.Interrupt = interrupt.New(sam.IRQ_SERCOM1_2, sercomUSART1.handleInterrupt)
+	sercomUSART2.Interrupt = interrupt.New(sam.IRQ_SERCOM2_2, sercomUSART2.handleInterrupt)
+	sercomUSART3.Interrupt = interrupt.New(sam.IRQ_SERCOM3_2, sercomUSART3.handleInterrupt)
+	sercomUSART4.Interrupt = interrupt.New(sam.IRQ_SERCOM4_2, sercomUSART4.handleInterrupt)
+	sercomUSART5.Interrupt = interrupt.New(sam.IRQ_SERCOM5_2, sercomUSART5.handleInterrupt)
+}
+
 const (
 	sampleRate16X = 16
 	lsbFirst      = 1
@@ -1950,6 +1963,11 @@ type USBCDC struct {
 	sent              bool
 }
 
+var (
+	// USB is a USB CDC interface.
+	USB = &USBCDC{Buffer: NewRingBuffer()}
+)
+
 const (
 	usbcdcTxSizeMask          uint8 = 0x3F
 	usbcdcTxBankMask          uint8 = ^usbcdcTxSizeMask

src/machine/machine_generic.go

@@ -165,3 +165,14 @@ func uartRead(bus uint8, buf *byte, bufLen int) int
 
 //export __tinygo_uart_write
 func uartWrite(bus uint8, buf *byte, bufLen int) int
+
+// Some objects used by Atmel SAM D chips (samd21, samd51).
+// Defined here (without build tag) for convenience.
+var (
+	sercomUSART0 = UART{0}
+	sercomUSART1 = UART{1}
+	sercomUSART2 = UART{2}
+	sercomUSART3 = UART{3}
+	sercomUSART4 = UART{4}
+	sercomUSART5 = UART{5}
+)