[ECOS] cyg_thread_delay vs cyg_flag_wait behavior

["Chase, Tom" <tomc at dtccom dot com>]

Hello,

I am working on my fourth ecos project.  Historically I have had a thread
monitoring a serial port.  The thread has the lowest priority and sits at a
getc until some data arrives then deals with it.  This has worked well for
debugging and configuration allowing a PC application to talk to the device
and set up frequencies or what not.

On the latest project this isn't working reliably.  It will work for a few
bytes of data then stop responding.  The change in performance appears to be
related to cyg_thread_delay vs. cyg_flag_wait.  For the first time, I have a
higher priority thread that has no cyg_thread_delays in it.  It sits at a
cyg_flag_wait most of the time (servicing flags every 100 to 250 ms).  If I
add a cyg_thread_delay to that thread (putting it just before the flag_wait
for example) then the serial behavior is as I expect.

I am working on an OMAP5912 and using the interrupt driven serial.  I have
verified that the thread is indeed waking up from the wait as I expect (10
times a second) and not always running (I.E. there is time available for
lower priority threads).  I have tried using various settings (buffered, non
buffered, stdin, TTY etc.) with no change in performance.  I have a
cyg_thread_delay that is called when the unit prepares to power down (to
lock out the keyboard) and any buffered serial inputs are handled then
(which is one clue to why this was happening).

I can add a delay but I would like to understand the differences between
these two functions while they are blocking.  Conceptually I think of the
delay and the wait doing the same thing and do not understand why they
behave differently while they are in effect.  Can anyone advise?  

Thanks,

Tom Chase
DTC Communications
Software Engineering Manager


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