TRAXMOD

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TRAXMOD is a lossless, portable digital audio player using the Microchip PIC32 high speed microcontroller chip (an older version used the NXP LPC2103 ARM7TDMI). Currently, TRAXMOD-PIC32 can play raw and FLAC wave audio streaming off of a FAT formatted MMC/SD Card at 44100Hz, 16 bits, stereo using a Burr-Brown PCM1770 DAC with integrated headphone amp. The old breadboarded TRAXMOD-ARM can play raw wave audio and 4 channel MOD files streamed off of a FAT formatted MMC/SD Card. Multichannel MOD playback is a future goal for the TRAXMOD-PIC32 player.

For more information about TRAXMOD, please read the FAQ. To see the TRAXMOD-ARM player in action, check out our YouTube demonstration video. Firmware source code, schematic diagrams, and board layout files can be found in the Developer's Area.

News

12-10-2009

This project has kind of stalled out for almost a year now... There are a couple good reasons why it made sense to put it on hold. Here's one of them:

Microchip is now producing their new PIC32 chips! The PIC32MX695F512H has 512+12KB of FLASH, 128KB of RAM, 3 SPI modules with 16 byte FIFOs, and 8 DMA channels. All of that still fits inside the same 64-pin TQFP package that we've successfully hand soldered before. Pricing is $7.01 in 100 unit quantity, which is unbeatable for a part with these goodies.

Today I got a shipment tracking number for a few samples to play with. I'm very excited about the possibilities of this new part. 128KB of RAM is so much more than what we've had to work with in the past. MP3 playback could become a snap. The 16 byte SPI FIFOs might help reduce bus contention between the DMA and CPU when trying to do SD Card data transfers in the background. If that works out, the streaming MOD player implementation could become a lot easier too.

Even the power efficient FLAC/WAV playing we've already got working could become far better with very little effort. Currently, power consumption is dominated by the SD Card. With more RAM inside the microcontroller, we could buffer more data from the SD Card, allowing the SD Card to power off for longer periods of time.

The only bad thing is that they don't offer one without integrated USB and 10/100Mbps Ethernet. That means the pinout might be different from what I was using before. I will need to find some time to work on finishing the next PCB revision so that we can start playing with this new chip.

Firmware v0.7.15 released. A few minor bug fixes here and there. Nothing major.

Spent a whole week trying to route a new PCB for the next hardware revision, but still not done. This new hardware revision will have a new power supply that is software controlled (hopefully it doesn't blow up on me). Using a manufactured double layer PCB, it will have a really tiny form factor so that the player can fit inside a AA battery enclosure. And it may finally have a little LCD to navigate and view song comments. Currently missing are surface mount LEDs for backlighting the LCD, physical clearance testing, copper fills, and of course, trying to pass DRC. And maybe some software testing on the existing hardware to verify that we can really bit-bang the DAC/LCD SPI this time instead of having to multiplex and route the MMC/SD Card SPI signals all over the board.

Firmware v0.7.14 released.
• Fixed bug in MOD player code that would let a Note Delay effect attempt to play a sample number that does not exist in the MOD file. This was causing the player to crash on certain MOD files.
  
  
• Fixed bug in MOD player that was overwriting sample finetune settings with 0. This caused notes in some MOD files to play at the wrong frequency.
  
  
• Moved all statically allocated MOD player variables to heap memory. This allows the other players (FLAC, etc) to use all available RAM like they had back in v0.7.12.
  
  
• Modified the FLAC decoder to generate decoded sample data in interleaved channel format instead of two separate output buffers for left and right channels. Eventually, this may allow us to improve the FLAC player by using the audio playback ring buffer directly in the decoder. Still need to add support for ring buffering in the decoder before that can happen though.

Firmware v0.7.13 released. This release adds some working, but poor MOD playback functionality to the PIC32 firmware. This firmware is basically a port of the old C only code from TRAXMOD-ARM v0.5, which does not do any streaming of sample data off of the SD Card. As a result, it can only play small MOD files where sample data fully fits inside the small 30KB of free RAM inside the PIC32. It has lots of bugs, but at least it makes sounds now.

Firmware v0.7.12 released.
• Reverted some of the DMA code back to v0.7.8 code. For some reason, 16-bit audio transfers to the DAC cost about 2.5mA more current than using 32-bit audio transfers, even though that reduces the audio buffer size by 50%.
  
  
• Gapless playback when playing across raw wave audio files is sometimes working now. We can still get hosed by EFSL slowness, but often times it does work. Only works when transistioning between files of the same type (switching between raw audio and FLAC compressed audio does not work gaplessly). Since FLAC leaves so little memory for the audio buffer, gapless playback across FLAC files probably does not work very often right now (if at all).
  
  
• Total power consumption for the whole device, excluding power supply losses, using my best Dane-Elec 2GB SD Card is: 15.5mA at 3.3V for raw audio and somewhere around 31mA for FLAC compressed audio. Using these numbers, my calculations indicate that a pair of 1000mAH AAA NiMH batteries could theoretically last up to 24 hours playing FLAC files, and up to 46.9 hours playing raw audio. Of course, real life is probably less than this, due to losses in the switching power supply (which I haven't measured) and due to most SD Cards drawing far more power than the Dane-Elec 2GB and Toshiba 2GB SD cards.
  
  There is lots of room for improvement in the FLAC power consumption, but even at this point we've got pretty good performance in my opinion. I measured the power consumption of a cheap $9 Emprex MP3 SD card player I've got, and my calculations indicate it would only last about 8 hours on a single AAA (it only accepts one AAA battery). Even if you doubled that for two batteries, 16 hours is still worse than our 24. I wonder how power efficient more expensive players are. Anyone know?

Firmware v0.7.11 released:
• Play/Pause works when playing FLAC files.
• Repeat mode works when playing FLAC files.
• Switching files early while playing FLAC files no longer stutters.
• Power management code added to FLAC playback loop. Still draws a lot of power (around 25mA), but its a start.

Firmware v0.7.10 released in the Developer's Area. This release adds support for FLAC files encoded with "-blocksize 2048" (or less). Some restructuring of the FLAC decoder software was begun for the goal of reducing memory requirements low enough for possible 4096 block size support at some point in the future. Not there yet, still a long way to go.

This release brings forward all of the old MOD player source code from the TRAXMOD-ARM firmware. While the code does compile, MOD playing is not working yet as there is still some missing MMC/SD Card streaming routines that haven't been written for the PIC32 port yet. And the inline assembly language mixer code of course needs to be re-written for MIPS architecture.

Firmware v0.7.9 released in the Developer's Area for TRAXMOD-PIC32. This release adds the first working FLAC playback support! Totally unoptimized and plenty buggy controls, but it's great to have it up and running. Currently, only supports 44.1KHz/16-bit FLAC files encoded using the "-blocksize" setting of 1024 or lower. Larger block sizes consume too much RAM to work right now. Since FLAC is lossless, you can easily transcode your existing files to 1024 blocksize without any loss of quality, you just get a slightly lower compression factor.

This release features a new SPI DAC left/right clock synchronization routine that modulates the SPI CKE clock edge setting, forcing the SPI shift buffer over until we read a perfectly aligned left/right clock signal on the SDI input pin. Previously, we didn't attempt any forced synchronization to the DAC left/right signal -- instead we relied on the DAC and SPI to stay in sync from power on reset. Unfortunately, that always left the SPI off by one bit, which we compenstated for by shifting audio data over one bit before sending it to the SPIBUF. To accomodate that shift, we had to use a 32-bit audio buffer, even though we really only have 16-bits of actual data. Now that the SPI is perfectly aligned with the DAC, we can use a 16-bit audio buffer, effectively doubling the apparent amount of RAM for audio buffering.

I spent a lot of time trying to make this version play raw audio gaplessly when switching files, but ultimately gave up. Its better than last verison, but still has an occassional pop when switching files. EFSL takes too much time between files for it to work right now. We either need to re-write parts of EFSL for greater speed or start loading information about the next song while the current song is still in the middle of playing. Both are big projects that aren't worth the effort right now.

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