[LinuxBIOS] [PATCH] v3: add a check for a termination member

[Carl-Daniel Hailfinger]

On 06.01.2008 05:52, ron minnich wrote:
> On Jan 5, 2008 5:11 PM, Peter Stuge <peter at stuge.se> wrote:
>   
>> On Sat, Jan 05, 2008 at 02:44:55PM -0800, ron minnich wrote:
>>     
>>> NOT finding a file should be efficient.
>>>       
>> Yes.
>>
>> Where do the delay come from? Can anyone measure the LPC?
>>     
>
> I will try to measure for you but remember it is  running uncached.
> Each and every access is a full LPC cycle, which is not really fast.
>   

IIRC the PCEngines alix.1c has parallel flash, so the following does not
apply to our current problem.

However, for all boards with LPC-to-SPI translation through a IT8716F
Super I/O chip, the following applies:
My calculations suggest that for optimal reads (4 bytes at a 4 byte
boundary) with the IT8716F SPI translation function, we need (1 byte
opcode + 3 bytes addr + 4 bytes data)* 8 = 64 clock cycles on the SPI
bus alone. With a maximum of 33 MHz for the SPI clock on that particular
chip (MUST verify that the chip is set to 33 MHz and not 16 MHz!), this
optimal read takes 2 usec. Smaller reads take at least 1.25 usec. On top
of the pure SPI bus time we have to add the time to transmit and receive
that data over LPC. In case we don't use the automatic LPC-to-SPI
translation and use the embedded SPI controller directly, the LPC
overhead is replaced by 6+ ISA port byte reads and 5 ISA port byte
writes, which is probably even slower.

Regards,
Carl-Daniel