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SPI CPHA not setting correctly

dibs
Associate II

‎2014-09-26 11:07 AM

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-------------------------------------------------

0690X00000605AUQAY.png

#stm32f4 #spi
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6 REPLIES 6
stm322399
Senior

‎2014-09-27 02:17 AM

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.

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dibs
Associate II

‎2014-09-27 03:33 PM

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. 

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dibs
Associate II

‎2014-09-28 04:40 AM

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)

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dibs
Associate II

‎2014-09-29 05:31 AM

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.

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stm322399
Senior

‎2014-09-29 06:39 AM

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.

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dibs
Associate II

‎2014-09-29 10:14 AM

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.

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