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

["frank_kienast" <>]

I just tried making val an unsigned short and using a length of 2 for the 
write.  Also tried making it unsigned long and using length 4 for write.  Same 
error in all cases.

I know I've successfully used dd before with the skip parameter to specify 
offset (that was in /dev/kmem but same idea).  I would assume dd would do an 
lseek, but for all I know it could use mmap too.


--- In  "Harold" <> wrote:
>
> 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" <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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