Difference between revisions of "GPIO Driver"

Revision as of 14:32, 10 March 2009

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

Note: This driver is currently only working on APF9328 based systems !

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 linux26-menuconfig

Then go in menu:

Device Drivers  
    --> Armadeus specific drivers
        <M> Armadeus GPIO driver
        <M> Armadeus Parallel Port driver

Exit and save your kernel configuration, then compile it:

 [host]$ make linux26

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       pins order: [31...0]
 #

• Configure the IO-Pins 30, 28, 23, 22 and 21 of PortB as outputs ('1'), all others as inputs ('0'):

 # 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 (pin 31 of portD):

 # cat /proc/driver/gpio/portDdir | sed "s/[0-1]\([0-1]\{31\}\)$/1\1/" > /proc/driver/gpio/portDdir
 # echo -ne "\x00" > /dev/gpio/PD31
 # echo -ne "\x01" > /dev/gpio/PD31

• Sets only bit 5 of portADir to 1:

 # cat /proc/driver/gpio/portAdir | sed "s/[0-1]\([0-1]\{'''5'''\}\)$/'''1'''\1/" > /proc/driver/gpio/portAdir

• Sets only bit 5 of portADir to 0:

 # cat /proc/driver/gpio/portAdir | sed "s/[0-1]\([0-1]\{'''5'''\}\)$/'''0'''\1/" > /proc/driver/gpio/portAdir

• You can put it in a shell function:

 setbit()
 {
     PORT=$1
     NB=$2
     VAL=$3
     cat $PORT | sed "s/[0-1]\([0-1]\{$NB\}\)$/$VAL\1/" > $PORT
 }

 # setbit /proc/driver/gpio/portAdir 5 0

• 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