C Programming

The BD Software C compiler is included on drive A: or drive B: if you have the CP/M filesystem loaded on the Micro SD card. The following text is an exert from the BDS C Wikipedia article.

BDS C (or the BD Software C Compiler) is a compiler for a sizeable subset of the C programming language, that ran on and generated code for the Intel 8080 and Zilog Z80 processors. It was the first C compiler for CP/M. It was written by Leor Zolman and first released in 1979 when he was 20 years old. "BDS" stands for "Brain Damage Software."

BDS C User's Guide

Refer to the BDS C User's Guide for more about the language and its implementation.

BDS C Symbol Length Limitations

BDS C is an early implementation of the C programming language. The biggest gotcha is that all identifiers/symbols are unique to 7 characters. For example, the following two variables are treated as the same symbol:

int variable1;
int variable2;

Both are treated as variabl. So, be careful when naming variables, functions, and other symbols as you get no compiler warnings or errors and your application will behave unexpectedly.

BDS C Creating and Initializing Variables

BDS C does not support creating and initializing global variables in one step. For example, the following code will not compile:

int count = 0; // This will not compile

Instead, you must create and initialize global variables in two steps:

int count; // Create the variable

main()
{
    count = 0; // Initialize the variable
    ...
}

Compile C applications

The CP/M disk image includes a simple HW.C (Hello, world) application. BDS C language has support for Intel 8080 CPU input and output port instructions. The HW.C application displays the system tick count, UTC, and local date and time, and then sleeps for 1 second. For more information about Intel 8080 IO port mappings, refer to Intel 8080 input and output ports.

Follow these steps to list, compile, link, and run the HW.C file:

1. List the hw.c file

   type hw.c
   

   /* Copyright (c) Microsoft Corporation. All rights reserved.
      Licensed under the MIT License. */
   
   /* C application to demonstrate use of Intel 8080 IO Ports */
   
   main()
   {
       unsigned c, l;
       char buffer[50];
   
       printf("\nHello from the Altair 8800 emulator\n\n");
   
       for (c = 0; c < 65535; c++)
       {
           printf("Count:%u\n", c);
           printf("System tick count: %s\n", get_port_data(41, buffer, 50));
           printf("UTC date and time: %s\n", get_port_data(42, buffer, 50));
           printf("Local date and time: %s\n\n", get_port_data(43, buffer, 50));
   
           sleep(1); /* Sleep for 1 second */
       }
   }
   
   /* Sleep for n seconds */
   sleep(seconds)
   char seconds;
   {
       outp(30, seconds); /* Enable sleep for N seconds */
       while (inp(30)); /* Wait for sleep to expire */
   }
   
   /* Get data from Intel 8080 IO port */
   char *get_port_data(port_num, buffer, buffer_len)
   int port_num;
   char *buffer;
   int buffer_len;
   {
       char ch;
       int index;
   
       index = 0;
   
       while ((ch = inp(port_num)) && index < buffer_len) {
           buffer[index++] = ch;
       }
       buffer[index] = 0x00;
   
       return buffer;
   }
   

2. Compile the hw.c file:

   cc hw
   

3. Link the hw application:

   clink hw
   

4. Run the hw application:

   hw
   

5. Stop the hw application by selecting Ctrl+C.

Editing files

See Editing Files for details about transferring, editing, compiling, and running C source files.