I have a frustrating problem where WaitOne does not return when I expect.
I am using an AutoResetEvent with an overlapped structure in a call to
WaitCommEvent. The data I am expecting on the serial port is 23 bytes long,
and is sent in response to a command.
I begin timing before sending the command, and display split times when
received data is signalled. The entire exchange of command and response is
over within 6 ms (I have checked this with a scope).
When WaitOne first returns there are 18 characters in the receive buffer,
and the split time is 5 ms. As this is not the complete message, I call
WaitOne again to wait for a signal that the remaining data has been
received.
WaitOne then takes 10 ms before returning, just to signal that the remaining
5 bytes have been received.
I do not understand why the bulk of the data can be received and signalled
in 5 ms, whilst the remaining few bytes take a whacking 10 ms to be
signalled. I have checked with a scope and there are no gaps in the data -
the received data comes in as a contiguous stream, less than 1 ms after the
command is received by the remote device.
I know this is a big ask, but can anyone think why such a thing would happen
with AutoResetEvents ?
TIA
Charles
1  3045 
And the answer is ...
The FT232AM chip that I am using has a fixed 16 ms latency when the buffer
is not full.
Charles
"Charles Law" <bl***@nowhere. com> wrote in message
news:Ol******** ******@tk2msftn gp13.phx.gbl... I have a frustrating problem where WaitOne does not return when I expect.
I am using an AutoResetEvent with an overlapped structure in a call to
WaitCommEvent. The data I am expecting on the serial port is 23 bytes
long, and is sent in response to a command.
I begin timing before sending the command, and display split times when
received data is signalled. The entire exchange of command and response is
over within 6 ms (I have checked this with a scope).
When WaitOne first returns there are 18 characters in the receive buffer,
and the split time is 5 ms. As this is not the complete message, I call
WaitOne again to wait for a signal that the remaining data has been
received.
WaitOne then takes 10 ms before returning, just to signal that the
remaining 5 bytes have been received.
I do not understand why the bulk of the data can be received and signalled
in 5 ms, whilst the remaining few bytes take a whacking 10 ms to be
signalled. I have checked with a scope and there are no gaps in the data -
the received data comes in as a contiguous stream, less than 1 ms after
the command is received by the remote device.
I know this is a big ask, but can anyone think why such a thing would
happen with AutoResetEvents ?
TIA
Charles
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