Bulletin number:  24
Products affected: D711D
Description: Bi-directional communication Unix/Transputer
Component: 
Date: Thu Mar 8 12:05:14 GMT 1990
-----

We have been asked several times how a C program on a Transputer can
talk (bi-directionally) to a C program on a unix host system.  I have
written a sample program to demonstrate the general principle
involved.

The sample consists of two programs "host" and "prog".  To show the
generality I have made two version of the prog binary, one for unix
(uprog), the other for transputer (tprog).

Prog reads a number from stdin, squares it and writes it to stdout.
If EOF is reached or the number input is -99 the message EOF is
written.

Host creates two (unnamed) pipes.  Fork is called to create a new
process.

The child process connects the two pipes to stdin and stdout and
exec's the prog process.  If the host program was given any parameter
when it was started it calls the transputer version, i.e. the iserver
with the name the transputer program.

The parent process closes unused ends of pipes, prepares for stream
i/o and enters a read write loop.  Any numbers typed in at the
keyboard are transfered by pipe to the child task (prog).  The results
are then read from the output pipe and printed on the terminal.

Almost all error checking has been omitted to clarify the example.

+file:host.c+---------------------------------------------------------
#include <stdio.h>
#include <sys/wait.h>

int host_to_prog[2], prog_to_host[2];
FILE *ho_to_pr, *pr_to_ho;
int flag;

void parent()
{
  char line1[80], line2[80];
  int looping;
  close(host_to_prog[0]);
  close(prog_to_host[1]);
  ho_to_pr = fdopen(host_to_prog[1], "w");
  pr_to_ho = fdopen(prog_to_host[0], "r");
  if (flag > 1) /* read booting transputer message */
    {
      fgets(line2, sizeof line2, pr_to_ho);
      printf("%s", line2);
    }
  for (looping = 1; looping == 1;)
    {
      if (gets(line1) == NULL)
        {
          looping = 0;
          fprintf(ho_to_pr, "-99\n");
          fflush(ho_to_pr);
        }
      else
        {
          fprintf(ho_to_pr, "%s\n", line1);
          fflush(ho_to_pr);
	}
      fgets(line2, sizeof line2, pr_to_ho);
      printf("%s", line2);
    }
  wait((union wait *)NULL);
}

void child()
{
      close(1);               /* fix stdout */
      dup(prog_to_host[1]);
      close(prog_to_host[0]);
      close(prog_to_host[1]);
      close(0);               /* fix stdin */
      dup(host_to_prog[0]);
      close(host_to_prog[0]);
      close(host_to_prog[1]);
      if (flag > 1) /* transputer version */
        execlp("iserver", "iserver", "-sb", "tprog.b4x", (char *) NULL);
      else /* unix version */
        execl("./uprog", "uprog", (char *) NULL);
}

int main(argc, argv)
int argc;
char *argv[];
{
  flag = argc;
  pipe(host_to_prog);
  pipe(prog_to_host);
  if (fork())
    parent();
  else
    child();
}
+file:prog.c+---------------------------------------------------------
#include <stdio.h>

main()
{
  int i, j, k;
  for (;;)
    {
      i = scanf("%d", &j);
      if ((i == EOF) || (j == -99))
        {
          printf("EOF\n");
          exit(0);
	}
      k = j * j;
      printf("%d %d\n", j, k);
      fflush(stdout);
    }
}
+file:makefile+-------------------------------------------------------
all : host uprog tprog.c4x

host : host.c
	cc host.c -o host

uprog : prog.c
	cc prog.c -o uprog

tprog.c4x : prog.c
	t4c prog
	ilink mainent.c4x crtl.lib prog.bin -o tprog.c4x
	iboot tprog.c4x
+endfile+-------------------------------------------------------------