SPI CPHA not setting correctly

dibs · ‎2014-09-26

Posted on September 26, 2014 at 20:07

I am seeing some strange behavior in my SPI port.

I expect that it will be set up as CPOL = 0, CPHA = 0 and for the bus to output 0xA5.

What I see is that not only is MOSI transitioning on the wrong edges, but the data appears shifted.

I have inserted my code and a scope capture of the output. Red is CS, Yellow is CLK, and Green is MOSI.

Any ideas as to what is going on here?

-------------------------------------------Code-------------------------------------------------

GPIO_InitTypeDef GPIO_InitStructure;

SPI_InitTypeDef SPI_InitStructure;

// Enable GPIO clk

RCC_AHB1PeriphClockCmd(EEPROM_MOSI_AHB1Periph_GPIOx, ENABLE);

RCC_AHB1PeriphClockCmd(EEPROM_MISO_AHB1Periph_GPIOx, ENABLE);

RCC_AHB1PeriphClockCmd(EEPROM_SCLK_AHB1Periph_GPIOx, ENABLE);

RCC_AHB1PeriphClockCmd(EEPROM_CS_AHB1Periph_GPIOx, ENABLE);

// Connect Pins to AF

GPIO_PinAFConfig(EEPROM_SCLK_GPIOx, EEPROM_SCLK_SOURCE, EEPROM_AF);

GPIO_PinAFConfig(EEPROM_MOSI_GPIOx, EEPROM_MOSI_SOURCE, EEPROM_AF);

GPIO_PinAFConfig(EEPROM_MISO_GPIOx, EEPROM_MISO_SOURCE, EEPROM_AF);

// Pin Configuration

GPIO_StructInit(&GPIO_InitStructure);

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_DOWN;

GPIO_InitStructure.GPIO_Pin = EEPROM_SCLK_PIN_x;

GPIO_Init(EEPROM_SCLK_GPIOx, &GPIO_InitStructure);

GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;

GPIO_InitStructure.GPIO_Pin = EEPROM_MOSI_PIN_x;

GPIO_Init(EEPROM_MOSI_GPIOx, &GPIO_InitStructure);

GPIO_InitStructure.GPIO_Pin = EEPROM_MISO_PIN_x;

GPIO_Init(EEPROM_MISO_GPIOx, &GPIO_InitStructure);

GPIO_SetBits(EEPROM_CS_GPIOx, EEPROM_CS_PIN_x);

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;

GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;

GPIO_InitStructure.GPIO_Pin = EEPROM_CS_PIN_x;

GPIO_Init(EEPROM_CS_GPIOx, &GPIO_InitStructure);

// Init SPI peripheral

// Enable SPI clk

EEPROM_CLK_INIT(EEPROM_CLK, ENABLE);

SPI_I2S_DeInit(EEPROM_SPIx);

SPI_StructInit(&SPI_InitStructure);

SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;

SPI_InitStructure.SPI_Mode = SPI_Mode_Master;

SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;

// CPHA = 0 CPOL = 0

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_8;

SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;

SPI_Init(EEPROM_SPIx,&SPI_InitStructure);

// Set so that the SPI Master does not think someone is trying to take over the bus (Sets SSI bit)

SPI_NSSInternalSoftwareConfig(EEPROM_SPIx,SPI_NSSInternalSoft_Set);

eeprom_csd();

SPI_Cmd(EEPROM_SPIx,ENABLE);

SPI_I2S_SendData(EEPROM_SPIx,0xA5);

-------------------------------------------Code-------------------------------------------------

#stm32f4 #spi

stm322399 · ‎2014-09-27

Posted on September 27, 2014 at 11:17

I must admit this trace bugs me, software looks good, and this shift shall not happen.

Is this possible for you to post a single file that compiles and produces the error for us to reproduce.

Also tell us which device you are using, and a few words about your HW target.

Last, do not configure GPIO for 50MHz where 25 MHz is good enough, this will reduce the overshoot on electrical signals.

dibs · ‎2014-09-27

Posted on September 28, 2014 at 00:33

The target is an STM32F407. I will put together a file this weekend that will be able to compile on any Chinesium breakout board (or your favorite ST dev-kit), and I will post it on this thread.

At first I thought that the CPHA signal was incorrect, but on closer inspection, it really looks like the data is shifted backwards in time by a half clock cycle. I am not sure how this is possible.

dibs · ‎2014-09-28

Posted on September 28, 2014 at 13:40

Here is a file that can compile. It is using v_1_0_2 of the st stdperiph libraries. I will scope it out myself later today and see if I get the same thing.

File:

// Defines ----------------------------------------------------------------

#include ''stm32f4xx.h''

#include ''stm32f4xx_spi.h''

#include ''stm32f4xx_gpio.h''

#include ''stm32f4xx_rcc.h''

// Defines ----------------------------------------------------------------

#define MOSI_AHB1Periph_GPIOx RCC_AHB1Periph_GPIOB

#define MOSI_GPIOx GPIOB

#define MOSI_SOURCE GPIO_PinSource15

#define MOSI_PIN_x GPIO_Pin_15

#define MISO_AHB1Periph_GPIOx RCC_AHB1Periph_GPIOB

#define MISO_GPIOx GPIOB

#define MISO_SOURCE GPIO_PinSource14

#define MISO_PIN_x GPIO_Pin_14

#define SCLK_AHB1Periph_GPIOx RCC_AHB1Periph_GPIOI

#define SCLK_GPIOx GPIOI

#define SCLK_SOURCE GPIO_PinSource1

#define SCLK_PIN_x GPIO_Pin_1

#define CS_AHB1Periph_GPIOx RCC_AHB1Periph_GPIOB

#define CS_GPIOx GPIOB

#define CS_SOURCE GPIO_PinSource12

#define CS_PIN_x GPIO_Pin_12

#define SPIx SPI2

#define CLK RCC_APB1Periph_SPI2

#define CLK_INIT RCC_APB1PeriphClockCmd

#define IRQn SPI2_IRQn

#define ISRHANDLER SPI2_ISRHandler

#define AF GPIO_AF_SPI2

void init_spi(void);

int main (void) {

init_spi();

}

void init_spi(void) {

GPIO_InitTypeDef GPIO_InitStructure;

SPI_InitTypeDef SPI_InitStructure;

// Enable GPIO clk

RCC_AHB1PeriphClockCmd(MOSI_AHB1Periph_GPIOx, ENABLE);

RCC_AHB1PeriphClockCmd(MISO_AHB1Periph_GPIOx, ENABLE);

RCC_AHB1PeriphClockCmd(SCLK_AHB1Periph_GPIOx, ENABLE);

RCC_AHB1PeriphClockCmd(CS_AHB1Periph_GPIOx, ENABLE);

// Connect Pins to AF

GPIO_PinAFConfig(SCLK_GPIOx, SCLK_SOURCE, AF);

GPIO_PinAFConfig(MOSI_GPIOx, MOSI_SOURCE, AF);

GPIO_PinAFConfig(MISO_GPIOx, MISO_SOURCE, AF);

// Pin Configuration

GPIO_StructInit(&GPIO_InitStructure);

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_DOWN;

GPIO_InitStructure.GPIO_Pin = SCLK_PIN_x;

GPIO_Init(SCLK_GPIOx, &GPIO_InitStructure);

GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;

GPIO_InitStructure.GPIO_Pin = MOSI_PIN_x;

GPIO_Init(MOSI_GPIOx, &GPIO_InitStructure);

GPIO_InitStructure.GPIO_Pin = MISO_PIN_x;

GPIO_Init(MISO_GPIOx, &GPIO_InitStructure);

GPIO_SetBits(CS_GPIOx, CS_PIN_x);

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_OUT;

GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;

GPIO_InitStructure.GPIO_Pin = CS_PIN_x;

GPIO_Init(CS_GPIOx, &GPIO_InitStructure);

// Init SPI peripheral

// Enable SPI clk

CLK_INIT(CLK, ENABLE);

SPI_I2S_DeInit(SPIx);

SPI_StructInit(&SPI_InitStructure);

SPI_InitStructure.SPI_Direction = SPI_Direction_2Lines_FullDuplex;

SPI_InitStructure.SPI_Mode = SPI_Mode_Master;

SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;

// CPHA = 0 CPOL = 0

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_8;

SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;

SPI_Init(SPIx,&SPI_InitStructure);

// Set so that the SPI Master does not think someone is trying to take over the bus (Sets SSI bit)

SPI_NSSInternalSoftwareConfig(SPIx,SPI_NSSInternalSoft_Set);

GPIO_ResetBits(CS_GPIOx, CS_PIN_x);

SPI_Cmd(SPIx,ENABLE);

SPI_I2S_SendData(SPIx,0xA5);

} // end - void init_spi(void)

dibs · ‎2014-09-29

Posted on September 29, 2014 at 14:31

I just tested this code on an independent hardware target and I am getting the same result.

stm322399 · ‎2014-09-29

Posted on September 29, 2014 at 15:39

I have no F407 to test, but it works as expected on F429 disco (swapping CLK from I1 to D3, and MOSI from B15 to C3).

Sorry I can't help more.

dibs · ‎2014-09-29

Posted on September 29, 2014 at 19:14

I found the problem, my scope had almost exactly a half clock cycle skew on the probe input for the clock. I am not sure how it ended up being so close, but I found it when I started varying the SPI baud rate and found that MOSI did not appear to be edge triggered....

A little embarrassing, but sometimes it is the measurement hardware and not the code.