SPI RX trouble on TI Sitara AM3358

timroberts

I've been working on an app in Qt and I've run into some trouble. My program needs to use SPI to communicate with a 22 bit ADC (Microchip MCP3551) attached to a load cell. I'm running the program on a TI Sitara AM3358 processor.

I know my system is connected to the ADC chip correctly, I can get values back from the chip in linux by using the hexdump command. I've also verified the connections using a logic analyser.

Where I'm running into trouble is communicating to the system inside of Qt. Earlier I had done some tests using a loopback and the program responds correctly to that. When I stop using the loopback and attach my pins to the ADC chip my logic analyser displays the values that I'm expecting but my Qt program does not give me usable information on my SPI port.

To be honest something is probably set up incorrectly, but I'm not sure where to begin looking. Relevant code snippets are below.

Thanks for any assistance.

@
#ifdef SPIDEBUG
//declare device to use
static const char* device = "/dev/spidev1.0";
//declare variables
int fd;
int ret;
BYTE mode = 0;
BYTE bits = 8;
DWORD speed = 5000000;
BYTE tx[255] = "639";
BYTE rx[255];

//open the SPI device
fd = open(device, O_RDWR);

//verify we opened the device properly
if (fd < 0)
    qDebug() << "can't open device";


 //spi mode

ret = ioctl(fd, SPI_IOC_WR_MODE, &mode);
if (ret == -1)
    qDebug() << "can't set spi mode";

ret = ioctl(fd, SPI_IOC_RD_MODE, &mode);
if (ret == -1)
    qDebug() << "can't get spi mode";


 //bits per word

ret = ioctl(fd, SPI_IOC_WR_BITS_PER_WORD, &bits);
if (ret == -1)
    qDebug() << "can't set bits per word";

ret = ioctl(fd, SPI_IOC_RD_BITS_PER_WORD, &bits);
if (ret == -1)
    qDebug() << "can't get bits per word";


 //max speed hz

ret = ioctl(fd, SPI_IOC_WR_MAX_SPEED_HZ, &speed);
if (ret == -1)
    qDebug() << "can't set max speed hz";

ret = ioctl(fd, SPI_IOC_RD_MAX_SPEED_HZ, &speed);
if (ret == -1)
    qDebug() << "can't get max speed hz";

//declare new instance of SPI Utilities
SPIUtils *x = new SPIUtils;
//send values over tx, receive data back in rx
x->SPItransfer(fd, tx, 3, rx);

qDebug() << rx;

//close file
::close(fd);

#endif

void SPIUtils::SPItransfer(int filedescriptor, BYTE *tx, BYTE Length, BYTE *rx)
{
//declare variables
int ret;
spi_ioc_transfer tr;

//set up SPI transfer structure
//set up tx buffer
tr.tx_buf = (unsigned long) tx;
//set up rx buffer
tr.rx_buf = (unsigned long) rx;
//set up length of message to send
tr.len = Length;
//set inter-character delay
tr.delay_usecs = 0;
//set max speed
tr.speed_hz = 5000000;
//set number of bits per word
tr.bits_per_word = 8;
//set up chip select
tr.cs_change = 0;
//not sure what this is
tr.pad = 0;

//set up SPI to send message
ret = ioctl(filedescriptor, SPI_IOC_MESSAGE(1), &tr);
//check result from SPI port setup
if (ret < 1)
{
    qDebug() << filedescriptor;
    qDebug() << ret;
    qDebug() << errno;
    qDebug() << "can't send spi message";
}

return;

}

@

SGaist

Hi,

Where/when are you calling the code in the SPIDEBUG ifdef ?

timroberts

Hi,

Its declared at the beginning of the file. I think I've figured the issue out. Turns out I'm an idiot. If you're going to use an array, you need to reference the array properly. Once I got my array issue sorted out, the rest fell into place.

Thanks anyways.

SGaist

Don't worry, missing an array initialization happened to all of use.

However, your ifdefed code should rather be integrated into your class. Floating like that in your file it should not even compile.