Difference between revisions of "GPIO Driver"

Revision as of 17:40, 1 August 2008

On this page, you will find all the informations needed to use the Armadeus GPIO driver.

Compilation

The first thing you have to do is to compile the driver. The only way to do that for the moment is to compile it as a module:

[host]$ cd armadeus/
[host]$ make linux-menuconfig

Then go in menu: Device Drivers ---> Armadeus specific drivers and choose <M> Armadeus GPIO driver + <M> Armadeus Parallel Port driver:

Exit and save your kernel configuration, then compile it:

[host]$ make linux

When compiled, you will obtain 2 modules in armadeus/target/linux/modules/gpio/:

• gpio.ko: this is the main driver. It should be loaded first and will allow you to easily control gpio pin from user space,
• ppdev.ko: this is an extension driver to add PPDEV emulation to gpio.ko. This way you will be able to emulate a standard parallel port on one GPIO port (to connect a textual LCD, for example).

Installation

You have to:

• reflash your rootfs or copy these modules on your target in /lib/modules/2.6.18.1/extra/gpio (don't forget modules.dep file),
• copy loadgpio.sh script on your rootfs in /etc/

After that you can launch:

# sh /etc/loadgpio.sh

or look inside this script if you want to manually enter the module parameters:

# modprobe gpio portB_init=0,0,0x00FFFF00,0,0,0,0,0,0x0FF00000,0,0,0,0,0,0,0x0FF00000

gpio module parameters are values for PORTA, PORTB, PORTC, PORTD configuration registers in following order: DDIR, OCR1, OCR2, ICONFA1, ICONFA2, ICONFB1, ICONFB2, DR, GIUS, SSR, ICR1, ICR2, IMR, GPR, SWR, PUEN,
If you don't know what these registers means, load the module without parameters !!

Driver usage

Directly with shell commands (through /proc & /dev filesystem)

GPIO driver is configurable through /proc interface:

• use /proc/drivers/gpio/portXdir to read (with cat) or set (with echo) pin direction (where X is your port name: A, B, C or D)
• then use /proc/drivers/gpio/portX to read (with cat) or write (with echo) pin status
• /proc/drivers/gpio/portXirq: configure if GPIO should be used as an interruptible one (ie blocking read)
• /proc/drivers/gpio/portXpullup: (de)activate i.MXL internal pull-up for that GPIO

Examples:

• See which IO-Pins of PortD are configured as inputs, and which one are outputs ('1' = output, '0' = input):

# cat /proc/driver/gpio/portDdir
01101100111100000110110011110000
#

• Configure the IO-Pins 30, 28, 23, 22 and 21 of PortB as outputs, all others are inputs:

# echo -n 01010000111000000000000000000000 > /proc/driver/gpio/portBdir

• Read the status/values of the IOs of PortB:

# cat /proc/driver/gpio/portB
00000000000011111111000000000000
#

• Set bits 30, 28 and 23 of PortB to '1', all other outputs to '0': <-- DEPRECATED, use /dev/gpio/ instead !

# echo -n 01010000100000000000000000000000 > /proc/driver/gpio/portB

• Blinks the LED on DevFull:

# cat /proc/driver/gpio/portDdir
01111111111111111111100001000000
# echo -n 11111111111111111111100001000000 > /proc/driver/gpio/portDdir
# echo -ne "\x00" > /dev/gpio/PD31
# echo -ne "\x01" > /dev/gpio/PD31

• Blocking read on the PortD pin 0:

# cat /dev/gpio/PD0

Directly with C program ( /proc filesystem)

After inserting the GPIO module, /proc entries are created in the filesystem, and so it's possible to directly use some Linux standard functions inside a C program, such as:

• fopen
• fwrite
• fread
• fclose

A little piece of code is the best way to understand quickly:

    int i;
    unsigned char dummy;
    FILE *GPIO,*GPIODIR;
    char buffer[32];
    char * bufferDir="00000000011111111000000000000000";
    char * buffer1=  "00000000000000011000000000000000";
    char * buffer2=     "00000000000001100000000000000000";
    char * buffer3=     "00000000000110000000000000000000";
    char * buffer4=     "00000000011000000000000000000000";
 
    GPIODIR = fopen("/proc/driver/gpio/portDdir","w");
    setvbuf(GPIODIR,buffer,_IONBF,32);
    fwrite(bufferDir, sizeof(char), strlen(bufferDir), GPIODIR);
    fclose(GPIODIR);
    GPIO = fopen("/proc/driver/gpio/portD","w");
    setvbuf(GPIO,buffer,_IONBF,32);
    while(1) {            
        fwrite(buffer1, sizeof(char), strlen(buffer1), GPIO);
        sleep(1);
        fwrite(buffer2, sizeof(char), strlen(buffer2), GPIO);
        sleep(1);
        fwrite(buffer3, sizeof(char), strlen(buffer3), GPIO);
        sleep(1);
        fwrite(buffer4, sizeof(char), strlen(buffer4), GPIO);
        sleep(1);
    }
    fclose(GPIO);
    return (0);

Directly from a C program with IOCTLs

There is another way to drive GPIO module: with IOCTLs on the right device node. ioctl() function is using flags to say what it must be done (read and write):

• GPIORDDIRECTION for reading direction of the concerned port
• GPIOWRDIRECTION for writing direction of the concerned port
• GPIORDDATA for reading data of the concerned port
• GPIOWRDATA for writing data of the concerned port

An example of code will give more explanation:

  int fd;
  int i;
  int iomask,result;    
  unsigned char dev_buffer[BUF_SIZE+1];
 
  if ((fd = open("/dev/gpio/portD", O_RDWR))<0) {
    printf("Open error on /dev/gpio/portD\n");
    exit(0);
  }
  printf("Opened on /dev/gpio/portD\n");
  iomask=0xFFFFFF00;
  ioctl(fd,GPIOWRDIRECTION,&iomask);
  iomask=0x003F0000;
  for (i=0;i<2;i++) {
    printf("Led ON\n");        
    iomask=0x007F8000;
    ioctl(fd,GPIOWRDATA,&iomask);
    sleep(1);
    ioctl(fd,GPIORDDATA,&iomask);
    printf("read /dev/gpio/portD 0x%x\n",iomask);
    printf("Led OFF\n");
    iomask=0x00000000;
    ioctl(fd,GPIOWRDATA,&iomask);
    sleep(1);
  }
  close(fd);
  exit(0);

Of course you'll need to declare in the include part, the following:

• sys/ioctl.h
• linux/ppdev.h

and define pragmas such as:

• GPIORDDIRECTION _IOR(PP_IOCTL, 0xF0, int)
• GPIOWRDIRECTION _IOW(PP_IOCTL, 0xF1, int)
• GPIORDDATA _IOR(PP_IOCTL, 0xF2, int)
• GPIOWRDATA _IOW(PP_IOCTL, 0xF3, int)

Links

• http://soekris.hejl.de/
• http://people.redhat.com/twaugh/parport/html/ppdev.html
• http://www.krugle.com/examples/p-yckfcEKjgfqvsNcB/drivertest.c
• AT91 way of doing it
• AVR32 way of doing it
• JiBee's way of doing it