From d266e44bc50c02f2049086e45900611f4ad53bb2 Mon Sep 17 00:00:00 2001
From: Ayke van Laethem <aykevanlaethem@gmail.com>
Date: Mon, 30 Sep 2019 14:21:52 +0200
Subject: [PATCH] machine/samd21: use pins specified in I2CConfig

Instead of configuring machine.I2C0, machine.I2C1, etc. statically,
allow the pins to be set using machine.I2CConfig. This will also
automatically configure the correct pin mode for each pin instead of
having to specify that manually.
---
 src/machine/board_arduino_nano33.go      |  8 +++---
 src/machine/board_circuitplay_express.go | 16 ++++++------
 src/machine/board_feather-m0.go          |  8 +++---
 src/machine/board_itsybitsy-m0.go        |  8 +++---
 src/machine/board_trinket.go             |  8 +++---
 src/machine/machine.go                   |  2 ++
 src/machine/machine_atsamd21.go          | 33 +++++++++++++++++++-----
 7 files changed, 52 insertions(+), 31 deletions(-)

diff --git a/src/machine/board_arduino_nano33.go b/src/machine/board_arduino_nano33.go
index 00cc387c..fba4e200 100644
--- a/src/machine/board_arduino_nano33.go
+++ b/src/machine/board_arduino_nano33.go
@@ -110,10 +110,10 @@ const (
 
 // I2C on the Arduino Nano 33.
 var (
-	I2C0 = I2C{Bus: sam.SERCOM4_I2CM,
-		SDA:     SDA_PIN,
-		SCL:     SCL_PIN,
-		PinMode: PinSERCOMAlt}
+	I2C0 = I2C{
+		Bus:    sam.SERCOM4_I2CM,
+		SERCOM: 4,
+	}
 )
 
 // SPI pins
diff --git a/src/machine/board_circuitplay_express.go b/src/machine/board_circuitplay_express.go
index ae1bca9d..6f7e34a1 100644
--- a/src/machine/board_circuitplay_express.go
+++ b/src/machine/board_circuitplay_express.go
@@ -94,15 +94,15 @@ const (
 // I2C on the Circuit Playground Express.
 var (
 	// external device
-	I2C0 = I2C{Bus: sam.SERCOM5_I2CM,
-		SDA:     SDA_PIN,
-		SCL:     SCL_PIN,
-		PinMode: PinSERCOM}
+	I2C0 = I2C{
+		Bus:    sam.SERCOM5_I2CM,
+		SERCOM: 5,
+	}
 	// internal device
-	I2C1 = I2C{Bus: sam.SERCOM1_I2CM,
-		SDA:     SDA1_PIN,
-		SCL:     SCL1_PIN,
-		PinMode: PinSERCOMAlt}
+	I2C1 = I2C{
+		Bus:    sam.SERCOM1_I2CM,
+		SERCOM: 1,
+	}
 )
 
 // SPI pins (internal flash)
diff --git a/src/machine/board_feather-m0.go b/src/machine/board_feather-m0.go
index 8c4dc759..57704cc5 100644
--- a/src/machine/board_feather-m0.go
+++ b/src/machine/board_feather-m0.go
@@ -73,10 +73,10 @@ const (
 
 // I2C on the Feather M0.
 var (
-	I2C0 = I2C{Bus: sam.SERCOM3_I2CM,
-		SDA:     SDA_PIN,
-		SCL:     SCL_PIN,
-		PinMode: PinSERCOM}
+	I2C0 = I2C{
+		Bus:    sam.SERCOM3_I2CM,
+		SERCOM: 3,
+	}
 )
 
 // SPI pins
diff --git a/src/machine/board_itsybitsy-m0.go b/src/machine/board_itsybitsy-m0.go
index 48a7a095..0d7248c6 100644
--- a/src/machine/board_itsybitsy-m0.go
+++ b/src/machine/board_itsybitsy-m0.go
@@ -75,10 +75,10 @@ const (
 
 // I2C on the ItsyBitsy M0.
 var (
-	I2C0 = I2C{Bus: sam.SERCOM3_I2CM,
-		SDA:     SDA_PIN,
-		SCL:     SCL_PIN,
-		PinMode: PinSERCOM}
+	I2C0 = I2C{
+		Bus:    sam.SERCOM3_I2CM,
+		SERCOM: 3,
+	}
 )
 
 // SPI pins
diff --git a/src/machine/board_trinket.go b/src/machine/board_trinket.go
index 7eec1f6f..d5acf8ee 100644
--- a/src/machine/board_trinket.go
+++ b/src/machine/board_trinket.go
@@ -79,10 +79,10 @@ const (
 
 // I2C on the Trinket M0.
 var (
-	I2C0 = I2C{Bus: sam.SERCOM2_I2CM,
-		SDA:     SDA_PIN,
-		SCL:     SCL_PIN,
-		PinMode: PinSERCOMAlt}
+	I2C0 = I2C{
+		Bus:    sam.SERCOM2_I2CM,
+		SERCOM: 2,
+	}
 )
 
 // I2S pins
diff --git a/src/machine/machine.go b/src/machine/machine.go
index e55b522d..a7863d8f 100644
--- a/src/machine/machine.go
+++ b/src/machine/machine.go
@@ -5,6 +5,8 @@ import "errors"
 var (
 	ErrInvalidInputPin  = errors.New("machine: invalid input pin")
 	ErrInvalidOutputPin = errors.New("machine: invalid output pin")
+	ErrInvalidClockPin  = errors.New("machine: invalid clock pin")
+	ErrInvalidDataPin   = errors.New("machine: invalid data pin")
 )
 
 type PinConfig struct {
diff --git a/src/machine/machine_atsamd21.go b/src/machine/machine_atsamd21.go
index 32febd02..1c5b676b 100644
--- a/src/machine/machine_atsamd21.go
+++ b/src/machine/machine_atsamd21.go
@@ -519,10 +519,8 @@ func defaultUART1Handler() {
 
 // I2C on the SAMD21.
 type I2C struct {
-	Bus     *sam.SERCOM_I2CM_Type
-	SCL     Pin
-	SDA     Pin
-	PinMode PinMode
+	Bus    *sam.SERCOM_I2CM_Type
+	SERCOM uint8
 }
 
 // I2CConfig is used to store config info for I2C.
@@ -552,11 +550,30 @@ const (
 const i2cTimeout = 1000
 
 // Configure is intended to setup the I2C interface.
-func (i2c I2C) Configure(config I2CConfig) {
+func (i2c I2C) Configure(config I2CConfig) error {
 	// Default I2C bus speed is 100 kHz.
 	if config.Frequency == 0 {
 		config.Frequency = TWI_FREQ_100KHZ
 	}
+	if config.SDA == 0 && config.SCL == 0 {
+		config.SDA = SDA_PIN
+		config.SCL = SCL_PIN
+	}
+
+	sclPinMode, sclPad, ok := findPinPadMapping(i2c.SERCOM, config.SCL)
+	if !ok || sclPad != 1 {
+		// SCL must be on pad 1, according to section 27.5 of the datasheet.
+		// Note: this is not an exhaustive test for I2C support on the pin: not
+		// all pins support I2C.
+		return ErrInvalidClockPin
+	}
+	sdaPinMode, sdaPad, ok := findPinPadMapping(i2c.SERCOM, config.SDA)
+	if !ok || sdaPad != 0 {
+		// SDA must be on pad 0, according to section 27.5 of the datasheet.
+		// Note: this is not an exhaustive test for I2C support on the pin: not
+		// all pins support I2C.
+		return ErrInvalidDataPin
+	}
 
 	// reset SERCOM
 	i2c.Bus.CTRLA.SetBits(sam.SERCOM_I2CM_CTRLA_SWRST)
@@ -582,8 +599,10 @@ func (i2c I2C) Configure(config I2CConfig) {
 	}
 
 	// enable pins
-	i2c.SDA.Configure(PinConfig{Mode: i2c.PinMode})
-	i2c.SCL.Configure(PinConfig{Mode: i2c.PinMode})
+	config.SDA.Configure(PinConfig{Mode: sdaPinMode})
+	config.SCL.Configure(PinConfig{Mode: sclPinMode})
+
+	return nil
 }
 
 // SetBaudRate sets the communication speed for the I2C.