Of Ogg and Apple
p2pnet.net News:- The idea that Apple’s iPod can’t play Ogg Vorbis files because of a lack of computational horsepower was mooted in a Gizmodo open letter to Apple, yesterday.
But that’s not the case, apparently.
Who says so?
None other than Monty, Xiph’s TD.
Now read on >>>>>>>>>>
OGG Vorbis on iPod: A Rebuttal
By Monty - Xiph.org
Hi there; it’s interesting to see one’s software being talked about by others as if it fell from the sky
First off, the original iPod does indeed have the horsepower for Ogg; the original Tremor codec written in C used approximately 40MHz of a Cirrus Maverick (720TDMI), an ARM7 chip somewhat more underpowered than the chip in the iPod. What the Maverick often has that many other DSPs don’t have is access to alot of memory. This was indeed a stumbling block for a while.
Since then, we’ve made three mostly seperate branches of the Tremor codec line (used in the Rio), each tailored to specific CPU and memory structural differences found in different DSP architectures. Hugo Fiennes didn’t mention which he was using… or if he was aware there are multiple different branches today (although I expect he is aware, it’s worth mentioning).
From the story:
"The 5002 has a "broken" cache (1 wait state per access for program or data, meaning you effectively have half the effective clock rate when running code from external memory). This means that running code that doesn’t fit in the internal 96kbyte SRAM of the player is very inefficient, both in terms of CPU cycles and power."
He didn’t say if he meant code, data or both, but modern Tremor can fit both comfortably into this space. This is still substantially faster than the ARM7 DRAM-based access Tremor was originally designed for (using SRAM as a random-replacement cache with 7-14 wait-states on a cache miss).
Also, he says it uses more power but also says they didn’t optimize much and so, they’re mostly using the stock ANSI C Tremor decoder, written by a single engineer (me) in a month as a ’starting point’ to help other engineers write a Vorbis decoder for their own platforms. The mp3 playback is likely handcoded assembly written by a professional team focused on only that task. This is in fact astounding! It’s also a testement to the power of good modern compilers. I smile every time GCC soundly beats me at optimizing.
I agree that the newer iPods are more likely to decode Ogg and Vorbis with ease. I do, however, strongly believe the original iPods can also do so with room and cycles to spare.
Monty
TD, Xiph.Org
