From 500ee8067d633c666562ccae57bd8a621f3b5f34 Mon Sep 17 00:00:00 2001 From: cn Date: Sun, 15 Sep 2019 21:47:30 +0200 Subject: [PATCH] machine/stm32f103xx: fix SPI frequency selection The SPI frequency is broken since https://github.com/tinygo-org/tinygo/commit/b8c326d710a88877413e550b06100d9b79373dcd added I2C interface and changed the unrelated `PCLK2 = HCLK/4` initialization to `PCLK2 = HCLK/1` (but I2C uses PCLK1 anyways). This commit changes all baud rate prescalers to be /4 compared to before. Note: it is not possible to find an equivalent for 125 KHz SPI speed, it will be too fast (`f = 72 MHz / 256`) --- src/machine/machine_stm32f103xx.go | 33 +++++++++++++++--------------- 1 file changed, 17 insertions(+), 16 deletions(-) diff --git a/src/machine/machine_stm32f103xx.go b/src/machine/machine_stm32f103xx.go index 40566a74..552e540b 100644 --- a/src/machine/machine_stm32f103xx.go +++ b/src/machine/machine_stm32f103xx.go @@ -202,24 +202,25 @@ func (spi SPI) Configure(config SPIConfig) { var conf uint32 - // set frequency + // set frequency dependent on PCLK2 prescaler (div 1) switch config.Frequency { case 125000: - conf |= stm32.SPI_BaudRatePrescaler_128 + // Note: impossible to achieve lower frequency with current PCLK2! + conf |= stm32.SPI_BaudRatePrescaler_256 case 250000: - conf |= stm32.SPI_BaudRatePrescaler_64 + conf |= stm32.SPI_BaudRatePrescaler_256 case 500000: - conf |= stm32.SPI_BaudRatePrescaler_32 - case 1000000: - conf |= stm32.SPI_BaudRatePrescaler_16 - case 2000000: - conf |= stm32.SPI_BaudRatePrescaler_8 - case 4000000: - conf |= stm32.SPI_BaudRatePrescaler_4 - case 8000000: - conf |= stm32.SPI_BaudRatePrescaler_2 - default: conf |= stm32.SPI_BaudRatePrescaler_128 + case 1000000: + conf |= stm32.SPI_BaudRatePrescaler_64 + case 2000000: + conf |= stm32.SPI_BaudRatePrescaler_32 + case 4000000: + conf |= stm32.SPI_BaudRatePrescaler_16 + case 8000000: + conf |= stm32.SPI_BaudRatePrescaler_8 + default: + conf |= stm32.SPI_BaudRatePrescaler_256 } // set bit transfer order @@ -345,11 +346,11 @@ func (i2c I2C) Configure(config I2CConfig) { // Disable the selected I2C peripheral to configure i2c.Bus.CR1.ClearBits(stm32.I2C_CR1_PE) - // pclk1 clock speed is main frequency divided by PCK1 prescaler (div 2) + // pclk1 clock speed is main frequency divided by PCLK1 prescaler (div 2) pclk1 := uint32(CPU_FREQUENCY / 2) - // set freqency range to pclk1 clock speed in Mhz. - // aka setting the value 36 means to use 36MhZ clock. + // set freqency range to PCLK1 clock speed in MHz + // aka setting the value 36 means to use 36 MHz clock pclk1Mhz := pclk1 / 1000000 i2c.Bus.CR2.SetBits(pclk1Mhz)