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
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