vgm-player-bbc

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VGM player for the 6502 BBC Micro

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# vgm-player-bbc

## VGM music players for the SN76489-based 6502 BBC Micro.

This project contains 6502 source code that will playback music using various file formats and playback techniques.

Despite the name of the project, the routines in this project do not play `.VGM` files "as-is" because VGM is quite a complex format that requires a lot of storage (for 8-bit computers anyway), so there are two principle ways the data is pre-processed into a more compact data format.

1. `VGMPLAY` Using [Vgm Converter](https://github.com/simondotm/vgm-converter) to create a compact `.RAW` or `.BIN` file version of the VGM data, which is then compressed using Exomizer.
2. `VGCPLAY` Using [Vgm Packer](https://github.com/simondotm/vgm-packer) to create a compressed `.VGC` file version of the VGM data, which is played back using a custom decoder.

For the second player, there are two types of playback engine:
1. Standard 50Hz playback
2. "Bass Enhanced" 50Hz playback with 6522 IRQ routines to synthesize squarewave frequencies below 122Hz that the 4Mhz SN76489 cannot normally reproduce

---

## `VGM` Player Usage

To create a compressed VGM file that will work with Vgm Player, use [Vgm Converter](https://github.com/simondotm/vgm-converter) as follows:

```
vgmconverter.py "file.vgm" -n -t bbc -q 50 -r "file.bin" -o "file.bbc.vgm" 
```
And then run [Exomizer](https://github.com/bitshifters/exomizer) (version 2.x) on the output binary to 
```
exomizer.exe raw -c -m 1024 "file.bin" -o "file.bin.exo"
```

---

## `VGC` Player Usage

To create a compressed VGC file that will work with Vgc Player, use [Vgm Packer](https://github.com/simondotm/vgm-packer) as follows:

```
vgm-packer.py "file.vgm" -o "file.vgc"
```
You can optionally add `-n` to use huffman for extra compression ratio (slightly slower decoding however as a tradeoff).

### Compiling the source
Import `lib\vgcplayer.h.asm` and `lib\vgcplayer.asm` into your BeebAsm project. Note that you should `INCLUDE "lib/vgcplayer.h.asm"` at the point where you declare your zeropage vars - see `vgc_demo.asm` for an example.

#### `vgcplayer.asm`

You can assemble this module a couple of ways and there are defines in `vgcplayer.h.asm` as follows:

`ENABLE_HUFFMAN`
* If set to TRUE, the decoder will be able to load standard `.vgc` files as well as ones that have been huffman compressed by `vgmpacker.py`
* If set to FALSE, the decoder will not include any code to decode huffman `.vgc` files so make sure you do not compress your `.vgm` files using the `-n` option with `vgmpacker.py`.

Huffman decoding is a fair bit slower, but does save 5-10% in compression ratio, so I recommend only using it for situations where you need maximum compression and CPU runtime & code size is not an constraint.

There are 2 main user routines:

`vgm_init()` - to initialize the player with a VGC data stream

`vgm_update()` - to refresh the player every 50Hz

See `vgcplayer.asm` for more information.

#### `vgc_demo.asm`
This is a BeebAsm project with some example 6502 code for the `vgcplayer.asm` library. Feel free to create a `.vgc` file from your favourite `.vgm`, and then just `INCBIN` it accordingly.

There are some examples in the `/music/vgc/` folder.

#### Memory Requirements
The standard decoder requires 8 zero page vars and ~740 bytes of code ram.

The Huffman enabled decoder requires 19 zero page vars and ~924 bytes of code ram.

Both decoders require a 2Kb page aligned workspace ram buffer which can be passed to the decoder via `vgm_init()`.

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