On Wed, 14 Jan 2015 16:23:32 +0300
"Amelkin, Aleksandr" <[email protected]> wrote:
> I noticed that it takes painfully long for flashrom to even simply read a
> 16MB flash chip
> using FT2232H (Olimex ARM-USB-TINY-H) programmer.
>
> The time it takes would be appropriate for kHz-range SPI clocks, not for
> 30MHz SPI clock
> that FT2232H provides.
>
> I checked with an oscilloscope and found out that there are long
> multi-millisecond delays between short (~150us) SPI clock bursts during
> simple chip read operation ('-r' or 'reading old flash chip contents'). The
> delays are 2ms for native Windows 7 64-bit on an Intel Core-i7 2600 @ 3.4GHz,
> or as long as 7ms for a Ubuntu Linux running in a virtual box on the same
> Windows machine.
>
> I didn't look any deeper though.
>
> Has anyone done any profiling or have any ideas as to what may be causing
> this behavior?
I suspect the main part of this is the latency of the (FTDI) USB
protocol. Maybe the performance of the flashrom driver can be improved
with bigger buffers/bursts of reads but I am not aware of any obvious
bottlenecks.
--
Kind regards/Mit freundlichen Grüßen, Stefan Tauner
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