On SPI stress testing on a mini2440 board.

Hi, I have a mini2440 board to which I have connected a TI MSP430 G2553 microcontroller. I am communicating via SPI from the mini2440 master to the MSP430 microcontroller slave. I am having a problem though. I have to put a chip select delay and hence I am waiting for 500 uS using udelay. Sometimes the data seems to skip or cause glitches when the load is high I think. I had connected 2 microcontrollers and it works fine when I stress test it. In case of the mini2440 board after quite some hours of continuous transfers I get glitches. Is udelay consistent? Thanks, Gautam.