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machine/stm32f103xx: fix SPI frequency selection

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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`)
This commit is contained in:
cn
2019-09-15 21:47:30 +02:00
committed by Ron Evans
parent 8cd2c7502e
commit 500ee8067d
1 changed files with 17 additions and 16 deletions
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src/machine/machine_stm32f103xx.go
+17 -16
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@@ -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)