lib/other/peekpoke.c

   1 /* Peek and poke using /dev/mem.
   2  *
   3  * Callers now ought to check the return values.
   4  *
   5  * Calling peek() requires read permission on /dev/mem, and consumes
   6  * a file descriptor.  Calling poke() requires write permission, and
   7  * consumes another file descriptor.
   8  */
   9
  10 #include <sys/types.h>
  11 #include <fcntl.h>
  12 #include <unistd.h>
  13
  14 _PROTOTYPE( int peek, (unsigned segment, unsigned offset));
  15 _PROTOTYPE( int poke, (unsigned segment, unsigned offset, unsigned value));
  16
  17 #define SEGSIZE 0x10
  18
  19 int peek(segment, offset)
  20 unsigned segment;
  21 unsigned offset;
  22 {
  23   unsigned char chvalue;
  24   static int infd = -1;
  25
  26   if (infd < 0) infd = open("/dev/mem", O_RDONLY);
  27   if (infd < 0 ||
  28       lseek(infd, (unsigned long) segment * SEGSIZE + offset, SEEK_SET) < 0 ||
  29       read(infd, (char *) &chvalue, (unsigned) 1) != 1)
  30         return(-1);
  31   return(chvalue);
  32 }
  33
  34 int poke(segment, offset, value)
  35 unsigned segment;
  36 unsigned offset;
  37 unsigned value;
  38 {
  39   unsigned char chvalue;
  40   static int outfd = -1;
  41
  42   chvalue = value;
  43   if (outfd < 0) outfd = open("/dev/mem", O_WRONLY);
  44   if (outfd < 0 ||
  45       lseek(outfd, (unsigned long) segment * SEGSIZE + offset, SEEK_SET) < 0 ||
  46       write(outfd, (char *) &chvalue, (unsigned) 1) != 1)
  47         return(-1);
  48   return(chvalue);
  49 }