Glowing an LED using GPIO in craneboard - embedded

Question

I'd like to use GPIO to turn on an LED in a craneboard (ARM processor). I'm very new to embedded programming. But, I'm quite good at C. I referred in some websites and learnt about GPIO related commands. I wrote a code, but I'm not quite sure in how to integrate it to the u-boot coding of the craneboard. I don't know where to start. Kindly guide me.
#define LED1 (1 << 6)
int getPinState(int pinNumber);
int main(void)
{
GPIO0_IODIR |= LED1;
GPIO0_IOSET |= LED1;
while (1)
{
GPIO0_IOCLR |= LED1;
}
}
int getPinState(int pinNumber)
{
int pinBlockState = GPIO0_IOPIN;
int pinState = (pinBlockState & (1 << pinNumber)) ? 1 : 0;
return pinState;
}

Answer 1

First of all, learn common bit (also pin in your case) manipulation expressions that you will use A LOT in embedded programming:
/* Set bit to 1 */
GPIO0_IODIR |= LED1; //output
/* Clear bit (set to 0) */
GPIO0_IOSET &= ~LED1; //low
/* Toggle bit */
GPIO0_IOSET ^= LED1;
Your while() loop actually does nothing, except for the first iteration, because the same logical OR operations do no change bit state (see logical table of this op). Also you should add delay, because if pin toggles too fast, LED might look like off all the time. Simple solution would look like:
while(1)
{
GPIO0_IOSET ^= LED1;
sleep(1); //or replace with any other available delay command
}
I do not have source files of U-Boot for Craneboard, so cannot tell you the exact place where to put your code, but basically there are several options: 1) add it in main(), where U-Boot start, thus hanging it (but you still have LED blinking!). 2) implement separate command to switch LED on/off (see command.c and cmd_ prefixed files for examples) 3) Integrate it in serial loop, so pin could be switched while waiting user input 4) build it as an application over U-Boot.
Get used to a lot of reading and documentation, TRM is your friend here (sometimes the only one). Also there are some great guides for embedded starters, just google around. Few to mention:
http://www.microbuilder.eu/Tutorials/LPC2148/GPIO.aspx (basics with examples)
http://beagleboard.org/ (great resource for BeagleBoard, but much applies to CraneBoard as they share the same SoC, includes great community).
http://free-electrons.com/ (more towards embedded Linux and other advanced topics, but some basics can also be found)
http://processors.wiki.ti.com/index.php/CraneBoard (official CraneBoard wiki, probably know this, but just in case)
P.S. Good luck in and don't give up!

Answer 2

If you want to do it in u-boot (and not in Linux), then you have to write an application for u-boot.
$5.12 of u-boot manual explains how to do it.
The source of u-boot provides some examples that you can use.

Answer 3

I'd like to add my answer. The coding that I have done previously was a generalized one. In craneboard, there are certain functions, that does the operation. So, I rewrote it accordingly. I included the file cmd_toggle.c in 'common' directory in the u-boot directory. And added it to the Makefile. The following code will make the LED to blink.
int glow_led(cmd_tbl_t *cmdtp, int flag, int argc, char *argv[])
{
int ret,i=0,num=0,ctr=0;
int lpin;
lpin=(int)strtoul(argv[1]);
ret=set_mmc_mux();
if(ret<0)
printf("\n\nLED failed to glow!\n\n");
else{
if(!omap_request_gpio(lpin))
{
omap_set_gpio_direction(lpin,0);
for(i=1;i<21;i++)
{
ctr=0;
if((i%2)==0)
{
num=num-1;
omap_set_gpio_dataout(lpin,num);
}
else
{
num=num+1;
omap_set_gpio_dataout(lpin,num);
}
udelay(3000000);
}
}
}
return 0;
}
U_BOOT_CMD(toggle,2,1,glow_led,"Glow an LED","pin_number");
I could've made this a little simpler by just using a while loop to repeatedly set it as 1 and 0.
This can be executed from the u-boot console as toggle 142, as I have connected the LED to the pin 142.
P.S
Thanks for all your guidance. A special thanks to KBart