README for MPEG decoder for 68k/ColdFire


Revision history:

21-oct-1999: First release with ColdFire support, and under GPL. (Rob Scott)


Backround:

After searching the net for a MP3 decoder that wasn't too big, didn't require
a pentium, and that I could make sense of, I discovered that Stéphane TAVENARD
had written a 68K based decoder. I was able to convince him that releasing
the code under GPL would be a good thing, and started porting it to ColdFire.
The port wasn't too difficult, mostly dealing with the executable size
limitations of the binfmt loader, and elminating the use of floating point
for table initialization.

Thanks to Stéphane for making this possible!

Building:

The makefiles are currently set up to build with the uClinux ColdFire tool
chain. Edit make.common to change the location of the toolchain. Go to
mpegdec_lib, perform a make, then go to mpegdec_demo and do another make.
This will result in a coldfire executable. If you wish to build an x86
version, comment out the ColdFire define the two directories' Makefiles,
and do a "make clean && make" in both directories. 

Running:

Currently, I copy the mpegdec_demo to the romfs/bin area, and do a make in
the uClinux directory, to have it included in the boot image. Then I use
NFS to mount a directory that has the MP3 files.

Performance:

I haven't done accurate timing, but on a 54 MHz 5206e processor, it seems
that decode is about .5 realtime. On a 90 MHz 5307 processor, it seems
close to real time. I lack audio output hardware to actually hear the results.

Caveats:

Currently, the mpegdec_demo reads in a fixed amount of data and decodes it.
It needs to be changed to continuously fill the mpeg data buffer, as the
decoder empties it.

Todo list:

Changing mpegdec_demo to continuously stream data.
Translate the existing 68K assembly language routines to ColdFire, in the
hope that decoding will get to real time on the 5206e.