Setting SPI0 as slave and read buffer data.

[simo zz]

Hello,

I am developing a C application to read from the SPI0 from the Beaglebone Black.

The test I am doing is with two Beaglebones, one configured as a slave which transmits data, and the other I want to act as slave.

Both run a kernel 4.4.20-ti-r43. The master it's working fine, but the slave it doesn't. The connection diagram I planned is attached as an image.

The device-tree for the slave Beaglebone Black is the following:

/dts-v1/;

/ {

compatible = "ti,beaglebone", "ti,beaglebone-black", "ti,beaglebone-green";

part-number = "BB-SPIDEV0";

version = "00A0";

exclusive-use = "P9.17", "P9.18", "P9.21", "P9.22", "spi0";

fragment@0 {

target = <0xdeadbeef>;

__overlay__ {

pinmux_bb_spi0_pins {

pinctrl-single,pins = <

0x150 0x30  /* CLK INPUT */

0x154 0x30  /* DSO INPUT */ 

0x158 0x10  /* DS1 OUTPUT */

0x15c 0x30  /* CS0 INPUT */

>;

linux,phandle = <0x1>;

phandle = <0x1>;

};

};

};

fragment@1 {

target = <0xdeadbeef>;

__overlay__ {

#address-cells = <0x1>;

#size-cells = <0x0>;

status = "okay";

pinctrl-names = "default";

pinctrl-0 = <0x1>;

ti,pio-mode;

channel@0 {

#address-cells = <0x1>;

#size-cells = <0x0>;

compatible = "spidev";

reg = <0x0>;

spi-max-frequency = <0xf42400>;

spi-cpha;

};

channel@1 {

#address-cells = <0x1>;

#size-cells = <0x0>;

compatible = "spidev";

reg = <0x1>;

spi-max-frequency = <0xf42400>;

};

};

};

__symbols__ {

bb_spi0_pins = "/fragment@0/__overlay__/pinmux_bb_spi0_pins";

};

__local_fixups__ {

fragment@1 {

__overlay__ {

pinctrl-0 = <0x0>;

};

};

};

__fixups__ {

am33xx_pinmux = "/fragment@0:target:0";

spi0 = "/fragment@1:target:0";

};

};

and the C code used to read from the SPI is the following 

#include <stdint.h>

#include <unistd.h>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <getopt.h>

#include <fcntl.h>

#include <libgen.h>

#include <sys/ioctl.h>

#include <sys/stat.h>

#include <linux/types.h>

#include <linux/spi/spidev.h>

void pabort(char *string)

{

    perror(string);

    abort();

}

void usage(char *progname)

{

    printf("usage: %s <device> \n", progname);

}

void spiRead(int fd, uint32_t *rxbuffer, uint8_t bits, size_t txlen, uint32_t spiSpeed)

{

    *rxbuffer = 0;

    struct spi_ioc_transfer tr =

    {

        .tx_buf = (uint32_t) 0,

        .rx_buf = (uint32_t) rxbuffer,

        .len = txlen,

        .delay_usecs = 1,

        .speed_hz = spiSpeed,

        .bits_per_word = bits,

    };

    if(ioctl(fd, SPI_IOC_MESSAGE(1), &tr) == -1)

    {

        perror("can't read SPI message");

        return;

    }

    else

        printf("SPI read: %x\n", *rxbuffer);

}

int main(int argc, char **argv)

{

    int spifd = 0;

    uint8_t mode = 3;

    uint8_t bits = 32;

    uint32_t speed = 500000;

    uint32_t rxVal = 0;

    close(spifd);

    spifd = open("/dev/spidev1.0", O_RDWR);

    if(spifd == -1)

    {

        close(spifd);

        pabort("open: ");

    }

    if(ioctl(spifd, SPI_IOC_WR_MODE, &mode) == -1)

        pabort("ioctl SPI_IOC_WR_MODE: ");

    if(ioctl(spifd, SPI_IOC_WR_BITS_PER_WORD, &bits))

        pabort("ioctl SPI_IOC_WR_BITS_PER_WORD: ");

    if(ioctl(spifd, SPI_IOC_WR_MAX_SPEED_HZ, &speed))

        pabort("ioctl SPI_IOC_WR_MAX_SPEED_HZ: ");

    while(1)

    {

        // printf("Sending message to %s\n", argv[1]);

        spiRead(spifd, &rxVal, bits, sizeof(rxVal), speed);

        // usleep(500000);

    }

    close(spifd);

    return 0;

}

However, the value read into rxBuffer is always 0xffffffff and from the SPI0_SCLK pin I can see the clock signal (through my oscilloscope) so the CLK pin is not set as input as device-tree source should configure.

From AM335x Technical Reference Manual, the SPI0 can be configured as Master and as Slave.
What's wrong in my setup or what is the additional setting I have to do to have the SPI working as slave ?

Thank you in advance.
Regards,
Simon

[mazbeen...@gmail.com]

Even I have the same problem, did you figure out why?

[Robert Nelson]

On Thu, Aug 2, 2018 at 5:24 PM, <mazbeen...@gmail.com> wrote:
> Even I have the same problem, did you figure out why?

You need v4.13.x+

https://elinux.org/Tests:MSIOF-SPI-Slave

https://fosdem.org/2018/schedule/event/hwenablement_linux_as_spi_slave/attachments/slides/2355/export/events/attachments/hwenablement_linux_as_spi_slave/slides/2355/Linux_as_an_SPI_Slave_Handouts.pdf

Regards,

--
Robert Nelson
https://rcn-ee.com/