[coreboot] Timings v2

[Kevin O'Connor]

On Tue, Apr 21, 2009 at 04:00:08AM +0200, Peter Stuge wrote:
> Kevin O'Connor wrote:
> > But, you have a good point about the LPC/FWH being a limit. Does
> > anyone know if 50ms is the lower limit on reading 63488 bytes from
> > flash?  It still seems high.
> 
> Memory Read is the cycle used by LPC chips, 1 byte at a time.
> Firmware Memory Read is used by FWH chips, 1/2/4/128 bytes at a time.
> Often only 1.
> 
> 1 byte LPC needs 21 LPC clocks, 630 ns * 63488 = 39997440 ns = 40 ms.
> 1 byte FWH needs 19 LPC clocks, 570 ns * 63488 = 36188160 ns = 36 ms.
> 
> I think you're as close as you will get without multibyte Firmware
> Memory Read:
> 
> 128 byte FWH needs 273 LPC clocks = 8.27 us * (63488/128) = 4.1 ms.

Thanks Peter.

I don't think my epia-cn has FWH.  With FWH, will a cache-line fill
result in a 128byte flash read, or does one have to implement special
instructions to make use of it?

As a side note, things will also improve a little with lzma
compression of the roms.

-Kevin