Improved description of tape format in source code comment.

[pdp11-bin2load] / bin2load.c

/*
* © 2020 Aaron Taylor <ataylor at subgeniuskitty dot com>
* See LICENSE.txt file for copyright and license details.
*/

#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <getopt.h>

#define VERSION 1

void
print_usage( char ** argv )
{
   printf( "bin2load v%d (www.subgeniuskitty.com)\n"
           "Usage: %s i <file> -o <file> [-a <address>]\n"
           "  -i <file>    Binary file to be written to tape.\n"
           "               For example, binary executable from 'pdp11-aout-objdump'.\n"
           "  -o <file>    New paper tape image for use with SIMH.\n"
           "  -a <address> Address on PDP-11 at which to load paper tape contents.\n"
           , VERSION, argv[0]
   );
}


int
main( int argc, char ** argv)
{
   int c;
   FILE * src = NULL;
   FILE * dst = NULL;
   uint16_t address = 01000; /* Default address to load tape contents. */

   while ((c = getopt(argc, argv, "i:o:a:h")) != -1) {
       switch (c) {
           case 'i':
               if ((src = fopen(optarg, "r")) == NULL ) {
                   fprintf(stderr, "ERROR: %s: %s\n", optarg, strerror(errno));
               }
               break;
           case 'o':
               if ((dst = fopen(optarg, "w+")) == NULL ) {
                   fprintf(stderr, "ERROR: %s: %s\n", optarg, strerror(errno));
               }
               break;
           case 'a':
               address = (uint16_t) strtol(optarg, NULL, 0);
               break;
           case 'h':
               print_usage(argv);
               exit(EXIT_FAILURE);
               break;
           default:
               break;
       }
   }

   if (src == NULL || dst == NULL) {
       print_usage(argv);
       exit(EXIT_FAILURE);
   }
   printf("Paper tape will load at address 0%o.\n", address);

   /*
    * SIMH Binary Loader Format
    *
    * Loader format consists of blocks, optionally preceded, separated, and
    * followed by zeroes. Each block consists of the following entries. Note
    * that all entries are one byte.
    *
    *     0001
    *     0000
    *     Low byte of block length (data byte count + 6 for header, excludes checksum)
    *     High byte of block length
    *     Low byte of load address
    *     High byte of load address
    *     Data byte 0
    *       ...
    *     Data byte N
    *     Checksum
    *
    * The 8-bit checksum for a block is the twos-complement of the lower eight
    * sum bits for all six header bytes and all data bytes.
    *
    * If the block length is exactly six bytes (i.e. only header, no data),
    * then the block marks the end-of-tape. The checksum should be zero.  If
    * the load address of this final block is not 000001, then it is used as
    * the starting PC.
    */

   uint16_t size = 6;

   uint16_t header[] = {1,0,01000};
   fwrite(header,6,1,dst);

   uint8_t byte;
   int read;
   do {
       read = fread(&byte,1,1,src);
       if(read == 1) fwrite(&byte,1,1,dst);
       size += read;
   } while (read == 1);

   uint16_t footer[] = {0,1,6,01000,0};
   fwrite(footer,10,1,dst);

   fseek(dst,2,SEEK_SET);
   fwrite(&size,2,1,dst);

   fclose(src);
   fclose(dst);
}