Re: [Ltib] Read from /dev/spi

[elex S]

Hello Peter,

Thanks for your inputs.
I checked 'linux/Documentation/spi' directory. It has sample program 'spidev_fdx.c'. I have tried it on my setup. 
I have following observations:
1. Function 'do_msg(int fd, int len)'  works well. 
  This function uses 'ioctl(SPI_IOC_MESSAGE)' mechanism to talk with slave.

2. Function 'do_read(int fd, int len)' always returns '0xff'.
  This function uses 'read()' call to get the data.

From #1, it seems that my kernel is configured with  'spidev'. However, #2 shows weird behaviour.

Would it be possible to provide more inputs so that I can dig into it?

Thanks,
Elex

Date: Mon, 01 Nov 2010 11:34:35 -0400
From: Peter Barada <address@hidden>
Subject: Re: [Ltib] Read from /dev/spi
To: address@hidden
Message-ID: <address@hidden>
Content-Type: text/plain; charset="iso-8859-1"

On 11/01/2010 10:57 AM, elex S wrote:
> Hello,
>
> I am using PHYTEC LPC3250 board. I want to write application that
> could do read/write over SPI bus. For that, I have enabled support for
> SPI while configuring LTIB.
> '' /proc/devices' shows SPI having major number '153'. Hence I have
> created the device nod '/dev/spi1' using following command:
>
>      $ mknod -m 666 /dev/spi1 c `cat /proc/devices | grep spi | head
> -c 4` 0
>
> Now, to test this I have decided to read/write over "SPI EEPROM".
> Write to eeprom works fine.(I have confirmed it using
> "/sys/bus/spi/devices/spi0.0/eeprom".)
> However read in following program always returns 0xFF.
>
> #include <stdio.h>
> #include <unistd.h>
> #include <fcntl.h>
> #include <string.h>
> #include <sys/ioctl.h>
> #include <sys/stat.h>
> #include <sys/time.h>
> #include <linux/types.h>
> #include <linux/spi/spidev.h>
> #include <sys/select.h>
> #include <errno.h>
>
> // Write Enable
> #define AT25_WREN 0x06
> // write disable
> #define AT25_WRDI  0x04
> //read status regs
> #define AT25_RDSR 0x05
> //write status regs
> #define AT25_WRSR 0x01
> //read data array
> #define AT25_READ 0x03
> //read data array
> #define AT25_WRITE 0x02
>
>
> int main(int argc, char* argv[])
> {
>
>     int file;
>     char filename[50] = {"/dev/spi1"};
>
>     unsigned char wr_buf[50] = {0};
>     unsigned char rd_buf[50] = {0};
>
>
>     file = open(filename, O_RDWR);
>     if (file < 0) {
>       printf("error in opening SPI file %s\n", filename);
>       /* ERROR HANDLING; you can check errno to see what went wrong */
>       exit(1);
>     }
>
>     wr_buf[0] = AT25_WREN;
>     if (write(file, wr_buf, 1) == -1) {
>       printf("error in writing to AT25_WREN \n");
>     }
>
>     usleep(100);
>
>     // write to EEPROM
>     wr_buf[0] = AT25_WRITE;
>     wr_buf[1] = 0x00;
>     wr_buf[2] = 0x00;
>     strcpy(&wr_buf[3],"Hello World");
>     if (write(file, wr_buf, 25) == -1) {
>       printf("error in writing \n");
>     }
>
>     usleep(100);
>
>     // send command to set RD address
>     wr_buf[0] = AT25_READ;
>     wr_buf[1] = 0x00;
>     wr_buf[2] = 0x00;
>
>     if (write(file, wr_buf, 3) == -1) {
>
>       printf("error in writing \n");
>     }
>     else
>     {
>       printf("no error in writing 2 \n");
>     }
>
>     usleep(100);
>
>     if (read(file, rd_buf, 5) == -1) {
>
>         printf("error inreading \n");
>       }
>
>     printf("\n rd buf = %s\n", rd_buf);
>
>     close(file);
>     return 0;
> }
>
>
>
> Could you please provide me pointer to solve the issue?

You really want to use spidev for this.

In your kernel source look at Documentation/spi/spidev for a description.
You'll have to modify the kernel source to add a "spidev" SPI device
which should cause udev (if you're running it) to create
"/dev/spidevX.Y" where "X" is the SPI bus and "Y" is the chip select on
that bus(both specified in the spidev SPI device).  Then you can write a
userspace program that can access the spi device using spi messages.


>
> Regards,
> Elex
>


--
Peter Barada
address@hidden