feather-stm32f405: add SPI support (#1377)

* machine/stm32f405: add SPI support

src/machine/board_feather-stm32f405.go

@@ -178,6 +178,22 @@ const (
 	SPI_SDO_PIN = SPI0_SDO_PIN //
 )
 
+var (
+	SPI1 = SPI{
+		Bus:             stm32.SPI2,
+		AltFuncSelector: stm32.AF5_SPI1_SPI2,
+	}
+	SPI2 = SPI{
+		Bus:             stm32.SPI3,
+		AltFuncSelector: stm32.AF6_SPI3,
+	}
+	SPI3 = SPI{
+		Bus:             stm32.SPI1,
+		AltFuncSelector: stm32.AF5_SPI1_SPI2,
+	}
+	SPI0 = SPI1
+)
+
 func initSPI() {}
 
 // -- I2C ----------------------------------------------------------------------

src/machine/machine_stm32_spi.go

@@ -20,15 +20,42 @@ type SPIConfig struct {
 }
 
 // Configure is intended to setup the STM32 SPI1 interface.
-// Features still TODO:
-// - support SPI2 and SPI3
-// - allow setting data size to 16 bits?
-// - allow setting direction in HW for additional optimization?
-// - hardware SS pin?
 func (spi SPI) Configure(config SPIConfig) {
+
+	// -- CONFIGURING THE SPI IN MASTER MODE --
+	//
+	// 1. Select the BR[2:0] bits to define the serial clock baud rate (see
+	// 	  SPI_CR1 register).
+	// 2. Select the CPOL and CPHA bits to define one of the four relationships
+	//    between the data transfer and the serial clock (see Figure 248). This
+	//    step is not required when the TI mode is selected.
+	// 3. Set the DFF bit to define 8- or 16-bit data frame format
+	// 4. Configure the LSBFIRST bit in the SPI_CR1 register to define the frame
+	//    format. This step is not required when the TI mode is selected.
+	// 5. If the NSS pin is required in input mode, in hardware mode, connect the
+	//    NSS pin to a high-level signal during the complete byte transmit
+	//    sequence. In NSS software mode, set the SSM and SSI bits in the SPI_CR1
+	//    register. If the NSS pin is required in output mode, the SSOE bit only
+	//    should be set. This step is not required when the TI mode is selected.
+	// 6. Set the FRF bit in SPI_CR2 to select the TI protocol for serial
+	//    communications.
+	// 7. The MSTR and SPE bits must be set (they remain set only if the NSS pin
+	//    is connected to a high-level signal).
+
+	// disable SPI interface before any configuration changes
+	spi.Bus.CR1.ClearBits(stm32.SPI_CR1_SPE)
+
 	// enable clock for SPI
 	enableAltFuncClock(unsafe.Pointer(spi.Bus))
 
+	// init pins
+	if config.SCK == 0 && config.SDO == 0 && config.SDI == 0 {
+		config.SCK = SPI0_SCK_PIN
+		config.SDO = SPI0_SDO_PIN
+		config.SDI = SPI0_SDI_PIN
+	}
+	spi.configurePins(config)
+
 	// Get SPI baud rate based on the bus speed it's attached to
 	var conf uint32 = spi.getBaudRate(config)
 
@@ -39,61 +66,72 @@ func (spi SPI) Configure(config SPIConfig) {
 
 	// set polarity and phase on the SPI interface
 	switch config.Mode {
-	case Mode0:
-		conf &^= (1 << stm32.SPI_CR1_CPOL_Pos)
-		conf &^= (1 << stm32.SPI_CR1_CPHA_Pos)
 	case Mode1:
-		conf &^= (1 << stm32.SPI_CR1_CPOL_Pos)
-		conf |= (1 << stm32.SPI_CR1_CPHA_Pos)
+		conf |= stm32.SPI_CR1_CPHA
 	case Mode2:
-		conf |= (1 << stm32.SPI_CR1_CPOL_Pos)
-		conf &^= (1 << stm32.SPI_CR1_CPHA_Pos)
+		conf |= stm32.SPI_CR1_CPOL
 	case Mode3:
-		conf |= (1 << stm32.SPI_CR1_CPOL_Pos)
-		conf |= (1 << stm32.SPI_CR1_CPHA_Pos)
-	default: // to mode 0
-		conf &^= (1 << stm32.SPI_CR1_CPOL_Pos)
-		conf &^= (1 << stm32.SPI_CR1_CPHA_Pos)
+		conf |= stm32.SPI_CR1_CPOL
+		conf |= stm32.SPI_CR1_CPHA
 	}
 
-	// set to SPI controller
-	conf |= stm32.SPI_CR1_MSTR
+	// configure as SPI master
+	conf |= stm32.SPI_CR1_MSTR | stm32.SPI_CR1_SSI
+
+	// enable the SPI interface
+	conf |= stm32.SPI_CR1_SPE
 
-	// disable MCU acting as SPI peripheral
-	conf |= stm32.SPI_CR1_SSM | stm32.SPI_CR1_SSI
+	// use software CS (GPIO) by default
+	conf |= stm32.SPI_CR1_SSM
 
 	// now set the configuration
 	spi.Bus.CR1.Set(conf)
-
-	// init pins
-	if config.SCK == 0 && config.SDO == 0 && config.SDI == 0 {
-		config.SCK = SPI0_SCK_PIN
-		config.SDO = SPI0_SDO_PIN
-		config.SDI = SPI0_SDI_PIN
-	}
-	spi.configurePins(config)
-
-	// enable SPI interface
-	spi.Bus.CR1.SetBits(stm32.SPI_CR1_SPE)
+	spi.Bus.CR2.SetBits((conf & stm32.SPI_CR1_SSM_Msk) >> 16)
 }
 
 // Transfer writes/reads a single byte using the SPI interface.
 func (spi SPI) Transfer(w byte) (byte, error) {
-	// Write data to be transmitted to the SPI data register
+
+	// 1. Enable the SPI by setting the SPE bit to 1.
+	// 2. Write the first data item to be transmitted into the SPI_DR register
+	//    (this clears the TXE flag).
+	// 3. Wait until TXE=1 and write the second data item to be transmitted. Then
+	//    wait until RXNE=1 and read the SPI_DR to get the first received data
+	//    item (this clears the RXNE bit). Repeat this operation for each data
+	//    item to be transmitted/received until the n–1 received data.
+	// 4. Wait until RXNE=1 and read the last received data.
+	// 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.
 	spi.Bus.DR.Set(uint32(w))
 
-	// Wait until transmit complete
-	for !spi.Bus.SR.HasBits(stm32.SPI_SR_TXE) {
+	// wait for SPI bus receive buffer not empty bit (RXNE) to be set.
+	// warning: blocks forever until this condition is met.
+	for !spi.Bus.SR.HasBits(stm32.SPI_SR_RXNE) {
 	}
 
-	// Wait until receive complete
-	for !spi.Bus.SR.HasBits(stm32.SPI_SR_RXNE) {
+	// copy input word (8-bit) in data register (DR), which was shifted in on MISO
+	// and parallel-loaded into register.
+	data := byte(spi.Bus.DR.Get())
+
+	// wait for SPI bus transmit buffer empty bit (TXE) to be set.
+	// warning: blocks forever until this condition is met.
+	for !spi.Bus.SR.HasBits(stm32.SPI_SR_TXE) {
 	}
 
-	// Wait until SPI is not busy
+	// wait for SPI bus busy bit (BSY) to be clear to indicate synchronous
+	// transfer complete. this will effectively prevent this Transfer() function
+	// from being capable of maintaining high-bandwidth communication throughput,
+	// but it will help guarantee stability on the bus.
 	for spi.Bus.SR.HasBits(stm32.SPI_SR_BSY) {
 	}
 
+	// clear the overrun flag (only in full-duplex mode)
+	if !spi.Bus.CR1.HasBits(stm32.SPI_CR1_RXONLY | stm32.SPI_CR1_BIDIMODE | stm32.SPI_CR1_BIDIOE) {
+		spi.Bus.SR.Get()
+	}
+
 	// Return received data from SPI data register
-	return byte(spi.Bus.DR.Get()), nil
+	return data, nil
 }

src/machine/machine_stm32f405.go

@@ -6,6 +6,7 @@ package machine
 
 import (
 	"device/stm32"
+	"math/bits"
 	"runtime/interrupt"
 )
 
@@ -46,8 +47,47 @@ type SPI struct {
 	AltFuncSelector stm32.AltFunc
 }
 
-func (spi SPI) configurePins(config SPIConfig)      {}
-func (spi SPI) getBaudRate(config SPIConfig) uint32 { return 0 }
+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)
+}
+
+func (spi SPI) getBaudRate(config SPIConfig) uint32 {
+	var clock uint32
+	switch spi.Bus {
+	case stm32.SPI1:
+		clock = CPUFrequency() / 2
+	case stm32.SPI2, stm32.SPI3:
+		clock = CPUFrequency() / 4
+	}
+
+	// limit requested frequency to bus frequency and min frequency (DIV256)
+	freq := config.Frequency
+	if min := clock / 256; freq < min {
+		freq = min
+	} else if freq > clock {
+		freq = clock
+	}
+
+	// calculate the exact clock divisor (freq=clock/div -> div=clock/freq).
+	// truncation is fine, since it produces a less-than-or-equal divisor, and
+	// thus a greater-than-or-equal frequency.
+	// divisors only come in consecutive powers of 2, so we can use log2 (or,
+	// equivalently, bits.Len - 1) to convert to respective enum value.
+	div := bits.Len32(clock/freq) - 1
+
+	// but DIV1 (2^0) is not permitted, as the least divisor is DIV2 (2^1), so
+	// subtract 1 from the log2 value, keeping a lower bound of 0
+	if div < 0 {
+		div = 0
+	} else if div > 0 {
+		div--
+	}
+
+	// finally, shift the enumerated value into position for SPI CR1
+	return uint32(div) << stm32.SPI_CR1_BR_Pos
+}
 
 // -- I2C ----------------------------------------------------------------------