Roughly implemented DOS beeping.

README.md

@@ -9,6 +9,17 @@ Currently a work in progress and very volatile.
 - Check framework, for running tests: `sudo apt install check`
 - ALSA development libraries for beep playback: `sudo apt install libasound2-dev`
 
+## DOS MIDI Player
+
+(WARNING: Experimental, extremely funny-sounding. Needs work! If you try it right now on a real machine, you will probably have to reboot that machine!)
+
+midibeep is a simple one-track MIDI player that can be cross-compiled for DOS from a modern UNIX-like system. Given a type 1 MIDI file and a track number, it will attempt to beep out that track on the PC speaker. It requires the OpenWatcom compiler to compile.
+
+- Ensure that `wcc` and `wcl` are in your PATH.
+- Ensure that the `WATCOM` environment variable is set to your watcom installation directory (e.g. `/opt/watcom`).
+- Ensure that the `INCLUDE` environment variable is set to the `h` subdirectory of your watcom installation directory (e.g. `/opt/watcom/h`).
+- Execute `make midibeep.exe` in the project root.
+
 ## References
 
 - https://web.archive.org/web/20140216225718/http://www.sonicspot.com/guide/midifiles.html

src/midibeep.c

@@ -7,6 +7,8 @@
 
 #ifdef USE_ALSA
 #include <alsa/asoundlib.h>
+#elif defined( USE_DOS )
+#include <dos.h>
 #endif /* USE_ALSA */
 
 #ifdef USE_MMAP
@@ -58,6 +60,31 @@ void beep( int freq_hz, int duration_ms ) {
       }
    }
 #elif defined( USE_DOS )
+   uint32_t freq_division = 0;
+   uint8_t prev_keyb_status = 0;
+
+   /* TODO: Needs cleanup with constants for port numbers, bitmasks, etc. */
+
+   freq_division = 1193180 / freq_hz;
+
+   /* Set the programmable interrupt timer to the given frequency. */
+   outp( 0x43, 0xb6 );
+   outp( 0x42, (uint8_t)freq_division );
+   outp( 0x42, (uint8_t)(freq_division >> 8) );
+
+   /* Set keyboard controller status to enable PC speaker. */
+   prev_keyb_status = inp( 0x61 );
+   if( prev_keyb_status != (prev_keyb_status | 0x03) ) {
+      outp( 0x61, (prev_keyb_status | 0x03) );
+   }
+
+   delay( duration_ms );
+
+   /* Turn off the PC speaker. */
+   prev_keyb_status = inp( 0x61 );
+   outp( 0x61, (prev_keyb_status & 0xfc) );
+
+   /* TODO: Reset the PIT to its previous frequency. */
 
 #endif /* USE_ALSA || USE_DOS */
 }