MUSIC3: a four-voice music player on a Cromemco D+7A

MUSIC3 plays "The Star Spangled Banner" in four voices. It sends the sound to the analog output of a Cromemco D+7A, which drives the speaker of joystick 1. This folder has the source, a CP/M machine that builds it, and a machine that plays it.

Play it

cd examples/d7a
altairsim music3.toml

The machine loads MUSIC3.HEX and runs it at 0100. The song takes about 60 seconds of emulated time. After the song, the program stops at an HLT. Press Ctrl-E to get the monitor prompt.

You hear the sound only on a build of altairsim that has a sound device. On another build, the program runs the same and the speaker is silent. To see that the speaker is in use, type SHOW d7a0 at the monitor prompt. The line speaker 1 says playing.

The processor is a Z80 at 4 MHz. The program uses the undocumented IYH and IYL instructions, and its frequency table is tuned for 4 MHz. Do not change clock_hz in music3.toml. With clock_hz = 0 the D+7A plays nothing.

Build it

The build runs in the guest. It needs no host tool.

1. Start the build machine from this folder:

cd examples/d7a altairsim music3-build.toml

2. Copy the source and the build commands from the folder to the CP/M disk:

A>R MUSIC3.ASM A>R MUSIC3.SUB

3. Run the build:

A>SUBMIT MUSIC3

MUSIC3.SUB runs two commands. M80 assembles the source and writes MUSIC3.REL and the listing MUSIC3.PRN. L80 links the program and writes MUSIC3.HEX. A correct build prints No Fatal error(s) and then the link map:

Data 0100 0610 < 1296>

4. Copy the results back to the folder. Use T for a text file:

A>W MUSIC3.HEX MUSIC3.HEX T A>W MUSIC3.PRN MUSIC3.PRN T

5. Press Ctrl-E to get the monitor prompt, and leave altairsim. Play the new file with altairsim music3.toml.

The R and W programs use the folder that you started altairsim from. Without T, W writes up to 127 Ctrl-Z bytes (1A) after the last line of a text file. LOAD ignores them, but the file is not clean.

MUSIC3.DSK has about 24K free before a build. A build writes over the MUSIC3.REL, MUSIC3.PRN and MUSIC3.HEX from an earlier build. The listing alone is about 65K. The disk is mounted read/write, so copy the image first if you want the original.

The program

• Four voices play at the same time. Each voice has a 16-bit counter that steps through a wave table with a note frequency from a frequency table.
• The four wave table values add together. The program subtracts 80h from the sum, and sends the result to the DAC with OUT (19h),A.
• The play loop takes 244 T-states, so the frequency table is right for a 4 MHz Z80 only.
• The score is the song table from BYTE magazine, volume 2, number 9 (September 1977), pages 77 and 78. A duration of 64 is a quarter note.
• The program puts its stack at the top of its 2K of working memory. It clears that memory before it plays.

The source

MUSIC3.ASM is MUSIC3.z80 by Dave Roberts (daver2), version 0.30. He posted it as MUSIC3 20240817.zip on 17 August 2024, in post 356 of the VCFed thread Cromemco JS-1 joystick replica. He wrote it for the ASM80 web assembler and emulator (asm80.com). The .emu file in his archive is the ASM80 emulator setup.

The source uses ASM80 syntax, which M80 does not accept. MUSIC3.ASM has these changes and no others. The code, the tables and the comments are his.

M80 does not accept an EQU that uses a label defined later in the file. For this reason, the EQU lines that use RAM are at the end.

DEBUG selects the build. DEBUG EQU 0 is the build in this folder. The program is at 0100, the tempo is 99h, and the sound goes to the DAC. DEBUG EQU 1 is the original debug build. The program is at 0000, the tempo is 06h, and the program prints hex values to the console at port 2 and makes no sound. With DEBUG EQU 1, M80 makes the same 1050 bytes as ASM80 makes from MUSIC3.z80. A .COM file needs DEBUG EQU 0.

Files