Access to gpio ressources (kernel space) (no gpiolib)

Hi everyone,

i am very beginner about the linux kernel and all that stuff.

I am using an Olimex lpc-h3131 board and i would like to develop a "gpio driver". For support, i have the linux device driver book chapter 9 "Commucating with hardware". Of course, gpiolib is not available.

For my first step, i have a led on the GPIO17 (adress 0x130031CB), i try to read the value on this pin. But it seems i don't do it correctly because the value read is always 0, even if the led is turned on ...

Any advices ?

you can find below a part of my driver :

#define GPIO_BASE 0x130031CB
void *map;

if(request_region(GPIO_BASE, 1, "parr_driver") != NULL)
{
	printk(KERN_ALERT "parr_driver : the adress GPIO16 is now reserved \n");

	if(request_mem_region(GPIO_BASE, 1, "parr_driver") != NULL)
	{
		printk(KERN_ALERT "parr_driver : the memory GPIO16 is now reserved \n");


		map = ioremap(GPIO_BASE, 1);

		if(map != NULL)
		{
			int byte = 0;
			printk(KERN_ALERT "parr_driver : ioremap worked : %p \n", map);
			byte = readb(map);
			printk(KERN_ALERT "parr_driver : byte : %i \n", byte);
		}
		else
		{
			printk(KERN_ALERT "parr_driver : ioremap failed \n");
		}	
	}
	else
	{
		printk(KERN_ALERT "parr_driver : the memory GPIO16 can't be reserved \n");
        }	
}
else
{
	printk(KERN_ALERT "parr_driver : the adress GPIO16 can't be reserved \n");
}

My output is the folowing :

parr_driver : the adress GPIO16 is now reserved parr_driver : the memory GPIO16 is now reserved parr_driver : ioremap worked : c286a1cb parr_driver : byte : 0

Documentation of the board :
http://www.olimex.com/dev/pdf/ARM/LPC/LPC-H3131.pdf
Documentation of the µC
http://ics.nxp.com/support/documents...30.lpc3131.pdf

My board is running under linux 2.6.33

Thanks for any helps, Livegen.
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second thread
Hi everyone,

i am very beginner in linux kernel and all that stuff.

I am developping a gpio driver for my Olimex lpc-h3131. the goal of this driver is to show the pin status. For support, i have the linux device driver book (chapter 9) "Communicating with the hardware".

I have done my driver and try to read the status on Pin 0x130031CB, a led is put on this pin. But it seems it don't work, because the value read is always 0 even if the led is turned on....

Any can help me ?

I am running under linux 2.6.33 patched for my board.

Documentation of the µC
http://ics.nxp.com/support/documents...30.lpc3131.pdf

Documentation of the board
http://www.olimex.com/dev/pdf/ARM/LPC/LPC-H3131.pdf

Livegen

I'm not sure if this is the case here, but it's not always possible to read the value of the output pin in a processor. To read the value, make sure the pin is set to input.