STM32F417 and LIS3DH SPI1 problem

slal · ‎2014-02-13

Posted on February 13, 2014 at 22:59

Hi forum!

Here is a very strange problem I'm facing with the SPI1 peripheral of the STM32F417 connected to the LIS3DH. I have to single-step through my code with my debugger in order to get the right data from the LIS3DH, otherwise I end up getting just 0xFF.

Here is my setup:

- PA4 set to OUT and Pull_UP used as CS♯ for LIS3DH, toggled by me through software.

- PA5/6/7 set to AF and PP.

- All pins at 50MHz, portA clock is enabled, SPI1 clock is enabled.

How I read a byte from the STM LIS3DH:

ACCEL_SELECT();

SPI1->DR = (uint8_t)(0x80 | reg); // set bit 7 to read

while( !(SPI1->SR & SPI_I2S_FLAG_TXE) );

SPI1->DR = 0x00; // dummy byte

while( !(SPI1->SR & SPI_I2S_FLAG_TXE) );

while( SPI1->SR & SPI_I2S_FLAG_BSY );

*data = (uint8_t)(SPI1->DR & 0xFF);

ACCEL_DESELECT();

Open to suggestions! Thanks!

#lis3dh #stm32f417

slal · ‎2014-02-13

Posted on February 13, 2014 at 23:04

And here's the init code just in case:

/* Accelerometer over SPI */

RCC_AHB1PeriphClockCmd( RCC_AHB1Periph_GPIOA, ENABLE );

RCC_APB2PeriphClockCmd( RCC_APB2Periph_SPI1, ENABLE );

SPI_I2S_DeInit(SPI1);

// GPIO setup

// CS#

gpio.GPIO_Pin = GPIO_Pin_4;

gpio.GPIO_Mode = GPIO_Mode_OUT;

gpio.GPIO_Speed = GPIO_Speed_50MHz;

gpio.GPIO_OType = GPIO_OType_PP;

gpio.GPIO_PuPd = GPIO_PuPd_UP;

GPIO_Init( GPIOA, &gpio );

ACCEL_DESELECT();

// Others

GPIO_PinAFConfig( GPIOA, GPIO_PinSource5, GPIO_AF_SPI1 ); // SPI1_SCK

GPIO_PinAFConfig( GPIOA, GPIO_PinSource6, GPIO_AF_SPI1 ); // SPI1_MISO

GPIO_PinAFConfig( GPIOA, GPIO_PinSource7, GPIO_AF_SPI1 ); // SPI1_MOSI

gpio.GPIO_Pin = GPIO_Pin_5 | GPIO_Pin_6 | GPIO_Pin_7;

gpio.GPIO_Mode = GPIO_Mode_AF;

gpio.GPIO_Speed = GPIO_Speed_50MHz;

gpio.GPIO_OType = GPIO_OType_PP;

gpio.GPIO_PuPd = GPIO_PuPd_NOPULL;

GPIO_Init( GPIOA, &gpio );

// Configure SPI

SPI_InitTypeDef spi;

spi.SPI_Direction = SPI_Direction_2Lines_FullDuplex;

spi.SPI_Mode = SPI_Mode_Master;

spi.SPI_DataSize = SPI_DataSize_8b;

spi.SPI_CPOL = SPI_CPOL_Low;

spi.SPI_CPHA = SPI_CPHA_1Edge;

spi.SPI_NSS = SPI_NSS_Soft;

spi.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_32;

spi.SPI_FirstBit = SPI_FirstBit_MSB;

SPI_Init(SPI1, &spi);

SPI_Cmd(SPI1, ENABLE);

francescatodiego · ‎2014-02-13

Posted on February 14, 2014 at 00:42

try changing

this

while( SPI1->SR & SPI_I2S_FLAG_BSY );

with

while(!( SPI1->SR & SPI_I2S_FLAG_RXNE ));

and also check the CS line

behavior

If

the switching of the

CS

line

is ''slow

'' add multiple call to CS selection

ACCEL_SELECT();

so

the start of communication

is

delayed

and CS is active when SPI start

slal · ‎2014-02-13

Posted on February 14, 2014 at 03:16

Thanks for your suggestions Diego. I've already tried both those approaches - they both don't help. I believe the BSY happens after RXNE anyways, right?

Also, if CS was slow, my writing would fail. But I don't have any issues while writing. It's only the reading that doesn't work - only works when I single step in the debugger.

francescatodiego · ‎2014-02-13

Posted on February 14, 2014 at 07:55

uint8_t dummy ;

ACCEL_SELECT();

SPI1->DR = (uint8_t)(0x80 | reg); // set bit 7 to read

while( !(SPI1->SR & SPI_I2S_FLAG_TXE) );

while( !(SPI1->SR & SPI_I2S_FLAG_RXNE) );

dummy = (uint8_t)(SPI1->DR & 0xFF); // Dummy read clr RXNE flag

SPI1->DR = 0x00; // dummy byte

while( !(SPI1->SR & SPI_I2S_FLAG_TXE));

while( !(SPI1->SR & SPI_I2S_FLAG_RXNE) );

*data = (uint8_t)(SPI1->DR & 0xFF);

ACCEL_DESELECT();

You must read the SPI RX register after each TX

The ST manual Note pag. 872

Note: Do not use the BSY flag to handle each data transmission or reception. It is better to use the TXE and RXNE flags instead.

slal · ‎2014-02-14

Posted on February 14, 2014 at 15:54

Thanks Diego, that helped! I had also tried it before, but thanks to your post I recognized a silly coding mistake on my part - my compiler was optimizing out the 'dummy' byte. This time I coded it again with 'volatile uint8_t dummy' instead, and it worked. Thanks, this is resolved.