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

["frank_kienast" <>]

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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