SPI generates clocks when set to 8b mode

[Linas L]

Posted on July 01, 2018 at 10:57

I have strange problem, SPI is sending 16 clocks instead of 8 as configured, and my trinamic motor driver simply does not work. Same code worked for STM32F415, right now i am using STM32F051

  GPIO_InitTypeDef  GPIO_InitStructure;

  SPI_InitTypeDef   SPI_InitStructure;  RCC_AHBPeriphClockCmd(RCC_AHBPeriph_GPIOA, ENABLE);  RCC_APB2PeriphClockCmd(RCC_APB2Periph_SPI1, ENABLE);   GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5|GPIO_Pin_6|GPIO_Pin_7;  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;  GPIO_InitStructure.GPIO_PuPd  = GPIO_PuPd_NOPULL;  GPIO_Init(GPIOA, &GPIO_InitStructure);  GPIO_PinAFConfig(GPIOA, GPIO_PinSource5, GPIO_AF_0);  GPIO_PinAFConfig(GPIOA, GPIO_PinSource6, GPIO_AF_0);   GPIO_PinAFConfig(GPIOA, GPIO_PinSource7, GPIO_AF_0);      SPI_I2S_DeInit(SPI1);  SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;  SPI_InitStructure.SPI_Mode = SPI_Mode_Master;  SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b; // define for it is ((uint16_t)0x0700)  SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;  SPI_InitStructure.SPI_CPHA = SPI_CPHA_1Edge;  SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;  SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_32;  SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;  SPI_InitStructure.SPI_CRCPolynomial = 7;  SPI_Init(SPI1, &SPI_InitStructure);  SPI_Cmd(SPI1, ENABLE);

It looks like normal code, so i don't know what to do now. If i set to 4 bits, it works (generates 8 clocks) , if i set to 8b i always get 16 clocks.

Is it some kind error in silicon? or in SPL libraries ?

Sending is done like this:

while(!SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_TXE));   

SPI1->DR=(uint8_t)address;while(!SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_RXNE));R=SPI1->DR;

[Tesla DeLorean]

Posted on July 02, 2018 at 01:59

>>Is it some kind error in silicon? or in SPL libraries ?

NO

The newer families of STM32 have a FIFO on the SPI, and queue a 16-bit write as a pair of 8-bit byte

while(!SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_TXE)); 

*((volatile uint8_t *)&SPI1->DR) = (uint8_t)address; // Do a 8-bit wide write at the peripheral bus

while(!SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_RXNE));

R=*((volatile uint8_t *)&SPI1->DR);

[Linas L]

Posted on July 06, 2018 at 11:26

I see now, it is more complicated.

digging to libraries i found different sending function: (Flag check is not included in send function)

  while(!SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_TXE));

  *(__IO uint8_t *) ((uint32_t)SPI1+0x0C) = data;  while(!SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_RXNE));  return *(__IO uint8_t *) ((uint32_t)SPI1+0x0C);

it always hangs on while(!SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_RXNE));

But if i comment it, i will get one cycle delay in my SPI register.

in other words, if i short MISO and MOSI, send 0xAA, i will get back 0, and second time, i will get 0xAA, so it i useless for my implementation.

How can i get clock in data with no latency ?

[waclawek.jan]

Posted on July 06, 2018 at 12:10

it always hangs on while(!SPI_I2S_GetFlagStatus(SPI1, SPI_I2S_FLAG_RXNE));

Should not.

If you observe the SPI registers using debugger, stop doing that.

JW

[Linas L]

Posted on July 06, 2018 at 12:14

I only observe global variables in real time so i know whats going on. i don't use debugger to see direct registers, only stepping code with debugger, that's all