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

["frank_kienast" <>]

Okay, but in both cases I'm using /dev/mem.  I'm not looking at my local memory 
space.  Isn't /dev/mem just a big file, that I should be able to seek within?

Thanks,
Frank


--- In  Jim Jackson <> wrote:
>
> 
> Because the memory map of your user space program is NOT the hardware 
> memory map of the hardware. mmap is a mechanism to map between them.
> 
> 
> 
> On Wed, 5 Jan 2011, 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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