USB to Serial port delay

I have some LabVIEW code that communicates with a TI MSP430 development board via a USB serial port simulator. The hardware that does the serial to USB conversion is part of the development board. how the application works is the LabVIEW code sends a request using the VISA write VI, and the board responds. The requests and responses are both about 5-6 bytes each, and are being sent at 115200 baud 8-N-1.
Everything works, but there is a roughly 600ms delay between sending the request and receiving the first byte of the response. After the first byte is received, the other bytes are received within 1 ms. I assumed the firmware in the develoment board was slow, but I put a scope on the RX and TX lines coming out of the microcontroller, and the firmware responds in less than 1 ms, so the microcontroller isn't the issue. So somewhere between the UART to USB hardware, and LabVIEW, there is a 600ms delay. I have a feeling that it is the TI development board, or drivers that are holding things up. The USB to serial stuff seems to be kind of flaky generally on these boards. However, I wanted to come on here, and see if anyone had any ideas about how I might figure this out, or what might be wrong. I'm going to post on the TI forums also, and see if I get a resonse there.
Has anyone seen an issue like this before using USB to serial converters?
Is there something else I could try to narrow down where the issue is, or rule out some part of the system (like making sure that it isn't an issue with the VISA drivers)?

Jeff·Þ·Bohrer wrote:
What is the USB-Serial chipset?
The FTDI drivers offer some latentcy optimizations. Others do not.
Most TI MSP430 boards have their own build in USB interface based on the TUSB3410 from TI and the according driver for it is the TUSBWINVCP package. Nothing to do with FTDI.
Rolf Kalbermatter
CIT Engineering Netherlands
a division of Test & Measurement Solutions

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Message was edited by: esmonde

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