stm32: support SPI on L4 series

lib/stm32-svd

@@ -1 +1 @@
-Subproject commit c6b5be976f440196dcd819a8d9a52c6786f67990
+Subproject commit 3a0b0829b70bf930c74fb69d887bee28005e7d99

src/machine/board_nucleol432kc.go

@@ -13,20 +13,53 @@ const (
 	LED_GREEN   = PB3
 )
 
-// UART pins
 const (
+	// Arduino Pins
+	A0 = PA0
+	A1 = PA1
+	A2 = PA3
+	A3 = PA4
+	A4 = PA5
+	A5 = PA6
+	A6 = PA7
+	A7 = PA2
+
+	D0  = PA10
+	D1  = PA9
+	D2  = PA12
+	D3  = PB0
+	D4  = PB7
+	D5  = PB6
+	D6  = PB1
+	D7  = PC14
+	D8  = PC15
+	D9  = PA8
+	D10 = PA11
+	D11 = PB5
+	D12 = PB4
+	D13 = PB3
+)
+
+const (
+	// UART pins
 	// PA2 and PA15 are connected to the ST-Link Virtual Com Port (VCP)
 	UART_TX_PIN = PA2
 	UART_RX_PIN = PA15
-)
 
-// I2C pins
+	// I2C pins
-const (
 	// With default solder bridge settings:
 	//    PB6 / Arduino D5 / CN3 Pin 8 is SCL
 	//    PB7 / Arduino D4 / CN3 Pin 7 is SDA
 	I2C0_SCL_PIN = PB6
 	I2C0_SDA_PIN = PB7
+
+	// SPI pins
+	SPI1_SCK_PIN = PB3
+	SPI1_SDI_PIN = PB5
+	SPI1_SDO_PIN = PB4
+	SPI0_SCK_PIN = SPI1_SCK_PIN
+	SPI0_SDI_PIN = SPI1_SDI_PIN
+	SPI0_SDO_PIN = SPI1_SDO_PIN
 )
 
 var (
@@ -40,15 +73,20 @@ var (
 		RxAltFuncSelector: 3,
 	}
 	UART1 = &UART0
-)
 
-var (
 	// I2C1 is documented, alias to I2C0 as well
 	I2C1 = &I2C{
 		Bus:             stm32.I2C1,
 		AltFuncSelector: 4,
 	}
 	I2C0 = I2C1
+
+	// SPI1 is documented, alias to SPI0 as well
+	SPI1 = &SPI{
+		Bus:             stm32.SPI1,
+		AltFuncSelector: 5,
+	}
+	SPI0 = SPI1
 )
 
 func init() {

src/machine/machine_stm32_spi.go

@@ -1,4 +1,4 @@
-// +build stm32,!stm32f7x2,!stm32l5x2,!stm32l4x2
+// +build stm32,!stm32f7x2,!stm32l5x2
 
 package machine
 
@@ -6,6 +6,7 @@ package machine
 
 import (
 	"device/stm32"
+	"runtime/volatile"
 	"unsafe"
 )
 
@@ -86,7 +87,12 @@ func (spi SPI) Configure(config SPIConfig) {
 
 	// now set the configuration
 	spi.Bus.CR1.Set(conf)
-	spi.Bus.CR2.SetBits((conf & stm32.SPI_CR1_SSM_Msk) >> 16)
+
+	// Series-specific configuration to set 8-bit transfer mode
+	spi.config8Bits()
+
+	// enable SPI
+	spi.Bus.CR1.SetBits(stm32.SPI_CR1_SPE)
 }
 
 // Transfer writes/reads a single byte using the SPI interface.
@@ -103,8 +109,10 @@ func (spi SPI) Transfer(w byte) (byte, error) {
 	// 5. Wait until TXE=1 and then wait until BSY=0 before disabling the SPI.
 
 	// put output word (8-bit) in data register (DR), which is parallel-loaded
-	// into shift register, and shifted out on MOSI.
+	// into shift register, and shifted out on MOSI.  Some series have 16-bit
-	spi.Bus.DR.Set(uint32(w))
+	// register but writes must be strictly 8-bit to output a byte.  Writing
+	// 16-bits indicates a packed transfer (2 bytes).
+	(*volatile.Register8)(unsafe.Pointer(&spi.Bus.DR.Reg)).Set(w)
 
 	// wait for SPI bus receive buffer not empty bit (RXNE) to be set.
 	// warning: blocks forever until this condition is met.

src/machine/machine_stm32f103.go

@@ -161,6 +161,10 @@ var (
 	SPI0 = SPI1
 )
 
+func (spi SPI) config8Bits() {
+	// no-op on this series
+}
+
 // Set baud rate for SPI
 func (spi SPI) getBaudRate(config SPIConfig) uint32 {
 	var conf uint32

src/machine/machine_stm32f405.go

@@ -67,6 +67,10 @@ type SPI struct {
 	AltFuncSelector uint8
 }
 
+func (spi SPI) config8Bits() {
+	// no-op on this series
+}
+
 func (spi SPI) configurePins(config SPIConfig) {
 	config.SCK.ConfigureAltFunc(PinConfig{Mode: PinModeSPICLK}, spi.AltFuncSelector)
 	config.SDO.ConfigureAltFunc(PinConfig{Mode: PinModeSPISDO}, spi.AltFuncSelector)

src/machine/machine_stm32f407.go

@@ -70,6 +70,10 @@ type SPI struct {
 	AltFuncSelector uint8
 }
 
+func (spi SPI) config8Bits() {
+	// no-op on this series
+}
+
 // Set baud rate for SPI
 func (spi SPI) getBaudRate(config SPIConfig) uint32 {
 	var conf uint32

src/machine/machine_stm32l0.go

@@ -184,6 +184,10 @@ type SPI struct {
 	AltFuncSelector uint8
 }
 
+func (spi SPI) config8Bits() {
+	// no-op on this series
+}
+
 // Set baud rate for SPI
 func (spi SPI) getBaudRate(config SPIConfig) uint32 {
 	var conf uint32

src/machine/machine_stm32l4.go

@@ -182,3 +182,67 @@ func enableAltFuncClock(bus unsafe.Pointer) {
 		stm32.RCC.APB2ENR.SetBits(stm32.RCC_APB2ENR_TIM1EN)
 	}
 }
+
+//---------- SPI related types and code
+
+// SPI on the STM32Fxxx using MODER / alternate function pins
+type SPI struct {
+	Bus             *stm32.SPI_Type
+	AltFuncSelector uint8
+}
+
+func (spi SPI) config8Bits() {
+	// Set rx threshold to 8-bits, so RXNE flag is set for 1 byte
+	// (common STM32 SPI implementation does 8-bit transfers only)
+	spi.Bus.CR2.SetBits(stm32.SPI_CR2_FRXTH)
+}
+
+// Set baud rate for SPI
+func (spi SPI) getBaudRate(config SPIConfig) uint32 {
+	var conf uint32
+
+	// Default
+	if config.Frequency == 0 {
+		config.Frequency = 4e6
+	}
+
+	localFrequency := config.Frequency
+
+	// set frequency dependent on PCLK prescaler. Since these are rather weird
+	// speeds due to the CPU freqency, pick a range up to that frquency for
+	// clients to use more human-understandable numbers, e.g. nearest 100KHz
+
+	// These are based on 80MHz peripheral clock frquency
+	switch {
+	case localFrequency < 312500:
+		conf = stm32.SPI_CR1_BR_Div256
+	case localFrequency < 625000:
+		conf = stm32.SPI_CR1_BR_Div128
+	case localFrequency < 1250000:
+		conf = stm32.SPI_CR1_BR_Div64
+	case localFrequency < 2500000:
+		conf = stm32.SPI_CR1_BR_Div32
+	case localFrequency < 5000000:
+		conf = stm32.SPI_CR1_BR_Div16
+	case localFrequency < 10000000:
+		conf = stm32.SPI_CR1_BR_Div8
+		// NOTE: many SPI components won't operate reliably (or at all) above 10MHz
+		// Check the datasheet of the part
+	case localFrequency < 20000000:
+		conf = stm32.SPI_CR1_BR_Div4
+	case localFrequency < 40000000:
+		conf = stm32.SPI_CR1_BR_Div2
+	default:
+		// None of the specific baudrates were selected; choose the lowest speed
+		conf = stm32.SPI_CR1_BR_Div256
+	}
+
+	return conf << stm32.SPI_CR1_BR_Pos
+}
+
+// Configure SPI pins for input output and clock
+func (spi SPI) configurePins(config SPIConfig) {
+	config.SCK.ConfigureAltFunc(PinConfig{Mode: PinModeSPICLK}, spi.AltFuncSelector)
+	config.SDO.ConfigureAltFunc(PinConfig{Mode: PinModeSPISDO}, spi.AltFuncSelector)
+	config.SDI.ConfigureAltFunc(PinConfig{Mode: PinModeSPISDI}, spi.AltFuncSelector)
+}

src/machine/spi.go

@@ -1,4 +1,4 @@
-// +build !baremetal stm32,!stm32f7x2,!stm32l5x2,!stm32l4x2 fe310 k210 atmega
+// +build !baremetal stm32,!stm32f7x2,!stm32l5x2 fe310 k210 atmega
 
 package machine