CARDS ON THE TABLE

Almost everyone knows how to use and program an SD card. There are a number of examples freely available. The embedded file system library (EFSL) is very popular. I used bits and pieces of my old code for the initialization and reading of files. My code covers only FAT16, but it’s rather small and uses very little RAM.

I put the open-source software for MP3 decoding into a separate directory (\fixpt) as part of CrossWorks for an ARM project. The compiler is based on GNU. There is a nice debugger in the package for easy development. Rowley offers a fully functional, time-limited evaluation version.

I was positively surprised that I had only a few compilation errors. After commenting out some unnecessary statements, everything compiled smoothly.

I haven’t used the dynamic memory allocation, but I have a rather static memory assignment. As a result, my mp3_init function is different, but you can do it either way. A dynamic allocation is more elegant because you can free up the memory for other uses.

My SD_play_mp3() function is based on the open source example. Only three functions from the package are called: MP3FindSyncWord(), MP3Decode(), and MP3GetLastFrameInfo(). I created the myFillReadBuffer() function to handle the readings from the SD card and filling the input buffer.

I usually use the “It’s not you, it’s me” approach when something doesn’t work. After fixing some bugs in my code, everything worked fine and I didn’t have a need to go any deeper into the MP3 code. If you’re curious about how it’s done, browse through the code and read the comments.

If it doesn’t work, you’re not hitting it with a big enough hammer. If your hardware is identical or similar to mine, you might first try to load the hex code using the Philips ISP utility. If it works and you need to make changes, you can rebuild the sources. Remember to turn on the optimization for the MP3 code in the GNU compiler. The “–Os” option worked for me.

There is no embedded video included in the project yet, but don’t be surprised if it’s as easy to do in the near future as it is to do today with embedded audio (that’s if Moore’s law still applies).

I’ve always admired people with artistic ability. Although embedded system design is more of a craft than an art, you can still make everything work well and look good.