Linux Application

Altera_Forum · ‎09-27-2004

Greetings, Long story here...

I have taken the Linux Ref Design provided by Microtronix and I have added a PIO -> user_pio. I have re-generated the system and compiled my design in Quartus. When I launch the IDE, I can create a NIOS II C Application and run code to write to my PIO (using IOWR_ALTERA_AVALON_PIO_DATA macro function).

When I create my Linux Application Project, it does not like the IOWR_ALTERA_AVALON_PIO_DATA macro - understandably since this macro is not supported in uC-Linux.

So... I have tried to access my pio using a FILE pointer such that:

FILE *fp_User_PIO = 0;
fp_User_PIO = fopen("/dev/user_pio","w");
if(fp_User_PIO==0)
   printf("Error opening User PIO\n");
// write AA to my PIO
fprintf(fp_User_PIO, "%d", 0xAA);

After adding this prog to my filesystem and running the program; it crashed. No suprise after realizing that my new PIO that I added does not exist in /dev (Note that the button_pio created by the ref design does exist as /dev/button)

So, I tried writing to my user_pio as memory:

char* pUserPIO = (char *)USER_PIO_BASE; // this is the base address for my user_pio defined in my system.h file (yes I have included it)
// write AA to my PIO
pUserPIO = 0xAA;

This too crashed. I am assuming this is standard practice with a "real" OS such that you don't want any yahoo writing to "just any" memory location.

I have considered using malloc() but figure this will grab a whole new hunk of memory.

Does anyone know how to write to my user_pio?

Should I add it to my FS as /dev/user_pio? If so, how?

Thanks,

-Terry

Altera_Forum · ‎09-27-2004

Hi Terry,

There are several approaches for you.

The "standard" way is to write a driver in kernel (the way Microtronix did for PIO buttons), implementing your PIO device as some kind of device Linux knows (the button is implemented as a character device). Then you can add the device node under /dev/ directory and read/write it as a file.

You can also take advantage of uClinux (no virtual memory and no memory protection) and read/write your device directly, but remember to bypass the cache. This is a quick (but dirty) approach. (It looks like you have tried this approach, but as long as you turned on the 31 bit of the USER_PIO_BASE, I don't think it caused the system crash).

Good luck,

wentao