Subject: Problems when accessing to registers in GPIO

From: "A. Nolson" <[email-masked]>
Date: Sat, 01 Mar 2008 23:10:56 +0100

Hi,

 I am getting some problems when trying to access to the GPIO registers 
from the userland of my secretlab's linux 2.6.24-rc3 ( Xilinx ML403 ). I 
am using io_remap() functions ( from 
http://www.denx.de/wiki/bin/view/PPCEmbedded/DeviceDrivers ) and I was 
successfully able to test them with some own-made IP cores. However, I 
am having problems when trying to do it in the same way with the GPIO IP 
core from Xilinx ( the ones I am using to interface to the LEDs , 
buttons and LCD ).

 If I try to access to the buttons in the board I don't really have any 
problem since the tri-state control register is automatically set to 
"all inputs" when the IP is turned on. But when I try to use the LEDs 
and I need to configure the tris-state as outputs, they don't work . I 
am doing the following:

    //memory mapping
    if(    (led_base = (volatile int*) ioremap(BASE_GPIO,8)) == NULL ||
            (but_base = (volatile int*) ioremap(BASE_GPIO_B, 8)) == NULL )
    {
        perror( "Cannot allocate memory for GPIO/n");
        return 1;
    }
     
    led_tri = (char*)led_base + 0x4;
    but_tri = (char*)but_base + 0x4;

    //configure as inputs and outputs
    printf("configuring IOs...");
    *led_tri = 0x00;//configure them as outputs
    *but_tri = 0xFF;//configure them as inputs

    while(1)
    {
        data = *but_base;
//     printf("data:%x\n",data);
       *led_base = data;
       usleep(50000);
    }   

 If I try to allocate the tri-state registers as integer I get "Bus 
Error" when accessing to them. I don't know really what is the problem. 
If I try to the same without operating system, this is, directly using 
XPS, I manage to make the buttons and leds work perfectly. Anybody can 
help me with this?

/A