I have been reading some stuff about non-PC MP3 players, generally those based on the STA013 MP3 decoder chip that you feed data over an I2C bus. With the higher speeds that the 6502 is now available at, I was wondering if anyone could comment on the practicality of using it as the core of a system to play MP3s with. The way I see it, the raw bus speed of a brand-new 65C02 @ 14 MHz is 14 MB/sec, and a rough average instruction time of ~4 clock cycles per instruction gives ~3.5 MIPS. (I love messing around with theoretical numbers.) MP3 data input methods ignored, what hardware would it take to push data to an I2C bus from a 6502, and about what bitrate would such a configuration be able to maintain, ignoring the time to bank-switch a chunk of memory, etc.?

Isn't the serial port on, say, the 6526 capable of being used as the underlying hardware for an I2C interface? It pumps out data and clock signals, and a parallel I/O line could be used to read the DATA_REQ pin from the STA013.

Just thought this might spark a little interest, the question has been floating in my head for a few days. I'm not a hardware genius so a little bit of the implementation of this thing is currently somewhat beyond my scope of knowledge.

If you found an MP3 decoder chip that uses an I²C interface, I really doubt that the resulting streaming audio samples go over I²C. I²C is normally good for only 400kbps because of the passive pull-up, which translates to only about 10,000 16-bit samples per second in stereo, meaning the high end of the frequency response would be under 5kHz.

The 6526 has been out of production for many years and never got anywhere near 14MHz (or 20MHz, which most of WDC's 65c02's are capable of), but the 65c22 is in production and can keep up. I have not researched any I²C interface ICs that could be put on the 65c02's bus, but the 6522 (or any other 65-family I/O IC) can only do it by bit-banging, and a fast 65c02 could indeed keep it going at or near full speed. The 6522's serial port is not I²C-compatible. It's almost SPI-compatible, but no cigar.

I don't have any information on the MP3 algorithm except that the data compression is something on the order of 13:1. I suppose that would mean that you could indeed feed it the unprocessed data over I²C fast enough. I've done audio sampling (record and playback) on the 65c02 at around 50,000 8-bit samples per second, one channel, interrupt-driven, with a 5MHz bus clock, and obviously you could do a lot better with 14MHz or more, a 65816, and DMA or even just shortening the interrupt process by using the WAIt instruction (which also cuts the jitter). The DSP required for the MP3 algorithm though would have to be left to the special IC.

http://www.pjrc.com/tech/mp3/sta013.html

This site has more info on interfacing the STA013 for an MP3 player. I am talking about transferring raw MP3-compressed data over the serial link into the chip, with I2C-based commands on a separate I2C bus. See the schematic on the page for visual info.

I made an error, the MP3 data does NOT go over I2C. Sorry.

This site also talks about using an 8051 to control the STA013 and last I checked that was an 8-bit microcontroller on the lower end of the speed spectrum, like the 65xx series are.

Further comment?

From the looks of things, the i2c commands do the configure, and it needs the mp3 data coming through a serial port setup. I can see the 65c02as teh master controllers, which I can fidn useful in sound porjects, but the fun matter is the storage circuitry since it is pretty much controlled from the mp3 chip when to feed the data in.

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