KL25z mbed SPI issue

gchen — Mon, 25 Nov 2013 18:42:09 GMT

Hey guys,

I'm new to the KL25z, and just picked it up and started programming it with the mBed libraries. There's one bug that I noticed, that I don't know how to fix. For some reason, when I program board to enable SPI communications with CPOL = 0 and CPHA = 1, the board doesn't adjust the phase correctly. The chip I'm interfacing with is the TI ADS1292, which communicates in that mode. When I interface the chip with an Arduino, it works just fine. Any suggestions on how I can fix this problem?

Thanks.

Re: KL25z mbed SPI issue

c0170 — Wed, 04 Dec 2013 14:03:25 GMT

Hello George Chen,

best would be to write this question on mbed directly, where we can help you much faster.

Can you share code,how you enable SPI with CPOL = 1 and CPHA = 1? Please, start a discussion there. Thanks.

Regards,

0xc0170

Re: KL25z mbed SPI issue

gchen — Wed, 04 Dec 2013 17:48:15 GMT

Thanks for responding,

I'm using the SPI library in mbed, which has a function format where I can specify the clock speed and mode

mbed-SPI Code

lines 31-36

void SPI::format(int bits, int mode) {

_bits = bits;

_mode = mode;

SPI::_owner = NULL; // Not that elegant, but works. rmeyer

aquire();

}

lines 47-53

void SPI::aquire() {

if (_owner != this) {

spi_format(&_spi, _bits, _mode, 0);

spi_frequency(&_spi, _hz);

_owner = this;

}

the function spi_format() called in aquire() is used to set up the registers for the clock speed and SPI mode.

from lines 95-113 in mbed-source code for spi_api.c

void spi_format(spi_t *obj, int bits, int mode, int slave) {

if (bits != 8) {

error("Only 8bits SPI supported");

}

if ((mode < 0) || (mode > 3)) {

error("SPI mode unsupported");

}

uint8_t polarity = (mode & 0x2) ? 1 : 0;

uint8_t phase = (mode & 0x1) ? 1 : 0;

uint8_t c1_data = ((!slave) << 4) | (polarity << 3) | (phase << 2);

// clear MSTR, CPOL and CPHA bits

obj->spi->C1 &= ~(0x7 << 2);

// write new value

obj->spi->C1 |= c1_data;

}

This code appears to be working fine, and I have been able to properly set up SPI in mode 0 and mode 3. It just doesn't seem to work for mode 1. I typically get zeros from the chip.

Below is my code.

#include "mbed.h"

#define RREG_COMMAND 0x20 //read command

#define WREG_COMMAND 0x40 //write command

SPI spi(PTC6, PTC7, PTC5); // mosi, miso, sclk

DigitalOut cs(PTD5); //chip select

DigitalOut afe(PTD0); //other SPI chip's chip select, set high throughout code to insure it doesn't interfere.

//Serial pc(USBTX, USBRX);

#define ID_ADDRESS 0x00 //register address to get ID of chip

#define CONFIG1_ADDRESS 0x01 //config 1 address

#define CONFIG2_ADDRESS 0x02 //config 2 address

#define LOFF_ADDRESS 0x03

#define CH1SET_ADDRESS 0x04

#define CH2SET_ADDRESS 0x05

#define RLD_SENS_ADDRESS 0x06

#define LOFF_SENS_ADDRESS 0x07

#define LOFF_STAT_ADDRESS 0x08

#define RESP1_ADDRESS 0x09

#define RESP2_ADDRESS 0x0A

#define GPIO_ADDRESS 0x0B

int read_register(int address) {

cs = 0;

wait(1);

int firstCommandByte = RREG_COMMAND | (address & 0x1F);

int secondCommandByte = 0x00;

printf("Sending 1 bit: %d\n",firstCommandByte);

printf("Sending 2 bit: %d\n",secondCommandByte);

spi.write(firstCommandByte);

spi.write(secondCommandByte);

int registerVal = spi.write(0x00);

printf("Result is %d\n",registerVal);

wait(1);

cs = 1;

return registerVal;

}

void write_register(int address, int value) {

cs = 0;

wait(1);

int firstCommandByte = WREG_COMMAND | (address & 0x1F);

int secondCommandByte = 0x00;

spi.write(firstCommandByte);

spi.write(secondCommandByte);

spi.write(value);

printf("Wrote %d in %d register\n",value,address);

wait(1);

cs = 1;

}

int main() {

cs =1;

afe = 1;

// Setup the spi for 8 bit data, mode 1

spi.format(8,1);

spi.frequency(2000000);

while(1) {

int value = read_register(ID_ADDRESS);

if (value == 115) {

printf("SUCCESS!");

}

else {

printf("%d\n",value);

}

value = read_register(CONFIG1_ADDRESS);

printf("%d\n",value);

wait(2);

//check if it's an issue with the function

cs = 0;

wait_ms(1000);

int firstCommandByte = RREG_COMMAND | (0x01 & 0x1F);

int secondCommandByte = 0x00;

printf("Sending 1 bit: %d\n",firstCommandByte);

printf("Sending 2 bit: %d\n",secondCommandByte);

spi.write(firstCommandByte);

spi.write(secondCommandByte);

int registerVal = spi.write(0x00);

printf("Result is %d\n",registerVal);

wait_ms(1000);

cs = 1;

write_register(CONFIG1_ADDRESS,0x01);

int confVal = read_register(CONFIG1_ADDRESS);

}

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