CMD/DILOG Q22 SCSI question

Hi list, I have a question for those of you who have fast CMD/DILOG Q22 SCSI controllers. Do you have trouble to run NetBSD 1.5.2 (maybe other 1.5.x too) on your Qbus VAX with CQBIC CDAL-Q22 controller? I found that if my board performed two burst mode DMA transactions in one DMA grant, the machine had machine check 10 errors (10us time out when CPU accessed memory that was mapped to the QBUS) from time to time. If I set the board to have one transaction a grant, there was no machine check 10 error. I read the diagram carefully and it seemed my board followed QBUS DMA protocal well. It was the CQBIC controller that prolonged the DMA (slow RPLY as response to DIN). I guess there are two solutions. One is that the software re-try the memory after machine check and keep going. The other is to stay with single shot DMA and be very slow. My guess is those fast CMD/DILOG boards have this problem with CQBIC too. If so, VMS would take the re-try approach. Could you conform or deny my guess? Thank you. My system is KA655 + two MS650-BA. Thank you. vax, 9000