Comparison of Clock Modes
=========================
Overview
~~~~~~~~
Compares vanilla SVN:20931 against various sync/async/fastbus clocking schemes. 

The schemes tested are in FS10191:synchronous_clocking_3.patch and FS10191:sync_async_clk_compare.patch (with per-test modifications to enbable particular configs, and to set DBOP_CLK=PCLK)

Items measured (on an e260v2):

1. Boosted MP3 decode performance
2. Unboosted LCD update rate. The e260v2 shows poor UI responsiveness when the clock is un-boosted - so it is interesting which schemes give the least bad performance.

Also attempted - a scheme where FCLK=MPMC_CLK=61MHz, PCLK=31MHz. This config does not boot (can't find .rockbox, and/or data abort). Probably needs more work on understanding the MPMC...

Summary
~~~~~~~
1. Vanilla 20931 seems to use an illegal unboosted clocking scheme: PCLK (61MHz) > FCLK (31MHz) in async mode. According to ARM DDI 0184B this is not a valid configuration.

2. Sync clocking seems to give ~5% improvement on boosted decode performance.

3. Vanilla 20931's illegal unboosted config gives the best LCD FPS. Sync clocking with FCLK/PCLK = 62/31MHz gives similar performance to vanilla 20931. Fastbus at 31MHz is about 25% worse than either of these.

Details
~~~~~~~
20931 vanilla
-------------
Un-boosted Clock Rates:
FCLK 31
PCLK 62
DBOP 31

Codec Test MP3 (VBR5):
163% 152MHz

LCD Update (FPS):
1/1 31
1/4 118
YUV (FPS):
1/1 15
1/4 60


20931 + FS10191:synchronous_clocking_3.patch  
--------------------------------------------
Un-boosted Clock Rates:
FCLK n/a
PCLK 31
DBOP 15

Codec Test MP3 (VBR5):
174% 143MHz

LCD Update (FPS):
1/1 18
1/4 70
YUV (FPS):
1/1 13
1/4 49

20931 + FS10191:synchronous_clocking_3.patch + DBOP=PCLK
--------------------------------------------------------
Un-boosted Clock Rates:
FCLK n/a
PCLK 31
DBOP 31

Codec Test MP3 (VBR5):
174% 143MHz

LCD Update (FPS):
1/1 24
1/4 93
YUV (FPS):
1/1 13
1/4 49


20931 + FS10191:sync_async_clk_compare.patch + async
----------------------------------------------------
Un-boosted Clock Rates:
FCLK 62
PCLK 31
DBOP 15

Codec Test MP3 (VBR5):
163% 153MHz

LCD Update (FPS):
1/1 21
1/4 81
YUV (FPS):
1/1 17
1/4 63

20931 + FS10191:sync_async_clk_compare.patch + sync
---------------------------------------------------
Un-boosted Clock Rates:
FCLK 62
PCLK 31
DBOP 15

Codec Test MP3 (VBR5):
174% 143MHz

LCD Update (FPS):
1/1 23
1/4 88
YUV (FPS):
1/1 17
1/4 64


20931 + FS10191:sync_async_clk_compare.patch + async + DBOP=PCLK
----------------------------------------------------------------
Un-boosted Clock Rates:
FCLK 62
PCLK 31
DBOP 31

Codec Test MP3 (VBR5):
163% 152MHz

LCD Update (FPS):
1/1 27
1/4 105
YUV (FPS):
1/1 17
1/4 65


20931 + FS10191:sync_async_clk_compare.patch + sync + DBOP=PCLK
---------------------------------------------------------------
Un-boosted Clock Rates:
FCLK 62
PCLK 31
DBOP 31

Codec Test MP3 (VBR5):
175% 142MHz

LCD Update (FPS):
1/1 30
1/4 114
YUV (FPS):
1/1 18
1/4 67