overrun error on PXI 8433/4 on RT target

[milaus]

hello,

I have this problem using the PXI 8433/4 board.

The application is for the OS RT Pharlap ETS.
The reader cycle has a rate of 100 Hz.
The producer sends 529 bytes each 25ms.
My application tryes to read 529*5 bytes (in order to avoid to accumulate bytes into the buffer of the serial board) each 10 ms.
I suppose the software jitter to be very little and a probe on the visa handle shows that the bytes at the port are always less than 500 (for how is possible to read this field at run-time).

How is possible that the buffer goes in overflow?
Is possible that the board has less than 2Kbytes of buffer?
Is possible that I have to explicitelly set the buffer size?

I use visa to handle six power supply (GPIB) and two serial links. Can this produce the problem?

thanks
Andrea

[LiciaP]

Hi Andrea,

as stated in the PXI 8433/4 specifications (which you can find here), the card has a buffer I/O FIFO of 128 B and this could explain the overrun errors if no flow control is used.

In this document you can find a detailed explanation of how serial devices and FIFO UART work, clarifing also why overrun errors are produced.

In this other document, possible explanations and resolutions are provided for buffer overflow errors.

In case you have not already done it, I also suggest to upgrade NI-Serial driver to last version (3.5), which might also help.

Eventually consider to implement hardware handshaking.

Hope this will help!

Bye!

Licia