[edk2-devel] On RPi4 and Juno, gBS->Stall(1) takes 10us and 100us respectively

[Rebecca Cran]

I've been doing some work on USB and ended up realizing that 
gBS->Stall(1) is taking much longer than it should: on my Juno R2 it's 
stalling for 100 us, while on my Raspberry Pi 4 it's 10 us.

This appears to be causing a USB bulk transfer request that asks for a 
1ms timeout taking 100ms on the Juno.

I'm measuring the delay with the following code:


UINT64 First = GetPerformanceCounter ();

gBS->Stall (XHC_1_MICROSECOND);

UINT64 Second = GetPerformanceCounter ();

UINT64 FirstNs = GetTimeInNanoSecond (First);
UINT64 SecondNs = GetTimeInNanoSecond (Second);

DEBUG ((DEBUG_INFO, "Stalled for %llu ns (%llu ms)\n", (SecondNs - 
FirstNs), (SecondNs - FirstNs) / 1024 / 1024));



I see output such as:

Stalled for 10500 ns (0 ms)


-- 
Rebecca Cran


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