[ts-7000] Re: TS7200 Accessing LEDs - Why must I use mmap()?

["Harold" <>]

In theory, I think, you should be able to write to physical memory by using 
lseek() & write() on /dev/mem, although I have never tried this myself.

Since you get "invalid argument", maybe it does not allow 1-byte writes. Have 
you tried writing 2 or 4 bytes?


--- In  "frank_kienast" <> wrote:
>
> Maybe I'm doing something stupid here, but it seems like I have to use mmap() 
> to access the LEDs on the TS7200.  The following works:
> 
> #include <sys/types.h>
> #include <unistd.h>
> #include <sys/stat.h>
> #include <sys/mman.h>
> #include <fcntl.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <unistd.h>
> 
> #define LED_ADDR 0x80840020
> 
> extern int errno;
> 
> 
> int main()
> {
>         int i;
>         unsigned char *leds;
>         unsigned char val;
> 
>         int fd = open("/dev/mem",O_RDWR|O_SYNC);
>         if(fd < 0)
>         {
>                 printf("Can't open /dev/mem\n");
>                 return 1;
>         }
>         leds = (unsigned char *) mmap(0, getpagesize(), PROT_READ|PROT_WRITE, 
> MAP_SHARED, fd, 0x80840000);
>         if(leds == NULL)
>         {
>                 printf("Can't mmap\n");
>                 return 1;
>         }
>         else
>                 printf("leds=%x\n",leds);
> 
>         for(i = 0; i < 256; i++)
>         {
>                 val = i % 4;
>                 leds[0x20] = val;
> 
>                 sleep(1);
>         }
> 
>         return 0;
> }
> 
> 
> But the following gets an error on the write
> System error:  22 = Invalid argument
> 
> #include <sys/types.h>
> #include <unistd.h>
> #include <sys/stat.h>
> #include <fcntl.h>
> #include <stdio.h>
> 
> #define LED_ADDR 0x80840020
> 
> extern int errno;
> 
> int main()
> {
>         int i;
>         off_t cs;
>         unsigned char val;
> 
>         int fd = open("/dev/mem",O_RDWR|O_SYNC);
>         if(fd < 0)
>         {
>                 printf("Can't open /dev/mem\n");
>                 return 1;
>         }
> 
>         for(i = 0; i < 256; i++)
>         {
> 
>                 cs=lseek(fd,LED_ADDR,SEEK_SET);
>                 if(cs != LED_ADDR)
>                 {
>                         printf("Can't lseek\n");
>                         return 1;
>                 }
>                 val = i % 4;
>                 cs=write(fd,&val,1);
>                 if(cs != 1)
>                 {
>                         printf("Write failed: %d\n",errno);
>                         return 1;
>                 }
> 
>                 sleep(1);
>         }
> 
>         return 0;
> }
> 
> 
> Shouldn't either method work?
> 
> Thanks,
> Frank
>




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