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Minimum hardware to support rockbox?

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scharkalvin:
If someone wanted to homebrew their own player hardware, what is the minimum that the Rockbox requires?  For example, is a Von Neuman type processor required, or would a Harvard type processor (IE: AVR) work?  Processor width (8, 16, 32 bits?).  How about minimum memory (program and data) required?  Speed (mhz, mips, instructions per second ?). 

The Chumby hacker board plus a cheap TFT LCD with touchscreen (you can get a 2.4" with TS and controller for about $20) for a total of under $100 (plus an SD card) would get you going.   

Atmel's Xmegas have up to 256kb (384mb soon) flash and can support several mb of external ram.  They have built in D/A with DMA support that might be usable for codecs.  Speed is only 32mhz (maybe can be overclocked a liltte) though.

saratoga:

--- Quote from: scharkalvin on February 23, 2011, 04:14:15 PM ---If someone wanted to homebrew their own player hardware, what is the minimum that the Rockbox requires?  For example, is a Von Neuman type processor required, or would a Harvard type processor (IE: AVR) work?  Processor width (8, 16, 32 bits?).  How about minimum memory (program and data) required?  Speed (mhz, mips, instructions per second ?). 
--- End quote ---

The HWCODEC targets (which use a hardware decoder rather then software decode) have ~12MHz CPUs and 1MB of RAM. 

The SWCODEC targets (which must run software decoders in RAM) require more.  The least amount of memory for any supported device is the ClipV1 with just 2MB of DRAM, and 320k of IRAM.  The slowest processor is probably the PP5002 which is a dual core ARM7TDMI running at 80MHz with very slow cache.  Faster processors allow for slower formats like AAC+ or APE to decode in real time.

All targets are >=32 bit.  16 or 24 bit would be very nearly impossible. 


--- Quote from: scharkalvin on February 23, 2011, 04:14:15 PM ---Atmel's Xmegas have up to 256kb (384mb soon) flash and can support several mb of external ram.  They have built in D/A with DMA support that might be usable for codecs.  Speed is only 32mhz (maybe can be overclocked a liltte) though.

--- End quote ---

Thats just a microcontroller.  You're going to need a real CPU.  Realistically I wouldn't bother with anything thats not ARM/Coldfire/MIPS. 

scharkalvin:

--- Quote from: saratoga on February 23, 2011, 04:21:48 PM ---Thats just a microcontroller.  You're going to need a real CPU.  Realistically I wouldn't bother with anything thats not ARM/Coldfire/MIPS. 
--- End quote ---

That's kinda what I thought.  Is a MMU (memory mapping unit for paged/segmented memory) with fault hardware required, or can a processor without  this (arm3-7) work?  Looks like the Chumby board would be about the lowest cost target point with the arm9 equal processor.

saratoga:

--- Quote from: scharkalvin on February 23, 2011, 05:21:24 PM --- Is a MMU (memory mapping unit for paged/segmented memory) with fault hardware required, or can a processor without  this (arm3-7) work?

--- End quote ---

An MMU is not required, and in fact we don't use VM at all.  We have lots of ARM7 targets.  Running on ARM before ARM7TDMI is probably not going to work though since you will need a modern multiplier unit if you plan on actually decoding audio.


--- Quote from: scharkalvin on February 23, 2011, 05:21:24 PM ---  Looks like the Chumby board would be about the lowest cost target point with the arm9 equal processor.

--- End quote ---

Thats probably a little bit more then you need.  Theres actually a lot of ARM9 dev boards on line for pretty cheap, although you may need to add your own screen.

scharkalvin:

--- Quote from: saratoga on February 23, 2011, 05:40:50 PM ---
--- Quote from: scharkalvin on February 23, 2011, 05:21:24 PM --- Is a MMU (memory mapping unit for paged/segmented memory) with fault hardware required, or can a processor without  this (arm3-7) work?

--- End quote ---

An MMU is not required, and in fact we don't use VM at all.  We have lots of ARM7 targets.  Running on ARM before ARM7TDMI is probably not going to work though since you will need a modern multiplier unit if you plan on actually decoding audio.


--- Quote from: scharkalvin on February 23, 2011, 05:21:24 PM ---  Looks like the Chumby board would be about the lowest cost target point with the arm9 equal processor.

--- End quote ---

Thats probably a little bit more then you need.  Theres actually a lot of ARM9 dev boards on line for pretty cheap, although you may need to add your own screen.

--- End quote ---

As long as I'm going to use an ARM9 it might make sense to just load a Linux port and look at Rockbox as an application running under Linux.  The idea of a mini Linux tablet is also interesting, though that DOES up the ante as far as the screen goes.  Lot's of cheap 240x320 touch screens out there, some under $20 but not suitable for X.  Getting up to 480x800 resolution in a 7" touch screen and you're at about the $110 price point.  This resolution is suitable for X windows, barely.

I could run command line Linux on a homebrew tablet with the QVGA screen, and rockbox would be fine with this resolution, however the number of suitable Linux apps would be limited.  The Chumby hacker board already has a Linux port ready to run.  I'll look around and see what else is out there.

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