On 4/4/17 5:19 PM, Benjamin Herrenschmidt wrote:
On Tue, 2017-04-04 at 12:32 -0500, Christopher Bostic wrote:
Agreed that there is room for improvement. I intend to look further
into your suggestions from here and our private conversation on the
matter and make changes as appropriate. I have an open issue to track
this. As it exists in this patch reads/writes from master to slave
fundamentally work.
My understanding is they "seem to work if you get lucky with the timing
and fall apart under load". Or did I hear wrong ?
Given the pervasiveness and time to fully evaluate
and test any protocol updates I intend address this in the near future
with a separate follow on patch.
Please try the simple change I proposed in my email. It's a 4 or 5
lines change max to your clock_toggle function and how it's called in
send and receive. It should be trivial to check if things still "seem
to work" to begin with.
Hi Benjamin,
I did try reordering the clock delays from: delay, clock 0, delay clock
1 to: clock 0, delay, clock 1, delay.
This worked fine. Making this change also removes the need for having a
third delay I had in place prior to sampling
SDA when in slave response mode.
A 3 microsecond delay is required, however, to prevent occasional issues
during heavy FSI bus load stress testing.
A 1 nanosecond delay using ndelay(1) had been specified prior to this
but after looking more closely at real time performance it turned out to
actually be roughly 1-2 microseconds. This appears to be the minimum
resolution using the delay() linux libraries on the AST2400/2500.
Given this, increasing delay to 3 microseconds doesn't impact
performance much considering I can now remove the sample input delay
based on your recommendations to re-order the two clock delays.
Thanks for your input.
Chris
Do you have some kind of test mechanism that hammers the FSI
continuously ? Such as doing a series of putmemproc/getmemproc &
checking the values ?
Then you can run that while hammering the LPC bus and generally putting
the BMC under load and you'll quickly see if it's reliable or not.
Cheers,
Ben.
