VAX - DRV11 Problem

Hi, I am working on a CF-18 simulator which is based on a VAX (No need to mention that the sim is old!). I am developing some hardware to allow some automatic testing of MC (mission Computer) OFP (Operational Flight Program) software. Anyway, I am working with a DRV11 card (DMA interface for the VAX), to communicate to an FPGA (APEX20K) board which I have built. The setup is shown below. |------------------| |-----------------------| |-----------------------| | Keypad | | | | | | & |--------------------------------------| My board |-----------------------| Serial | | display | | | | Controller | |------------------| |-----------------------| |-----------------------| | | | |-----------------------| | | | VAX | | | |-----------------------| Normally the keypad and display would be connected directly, but now I can contol the data via my board. What the board does depends on the VAX commands sent to it. This way, the board can become transparent, pump data in 1 direction or the other, or just plain monitor the data. The vax can then validate that everything that is supposed to happen does, and it will become possible to write scripts to press buttons on the keypad rather than having someone push the actual button! Anyway, my problem is with the DRV11 card. (Actually I am using a DRV1-SF) I have taken the DEC supplied example driver for this card and modified it for my needs. (this works fine... I think!) The problem is that if I send several QIO calls back to back, there is a huge amount of time between the DMA transfers. What makes this even wierder, is that the delay between transfers seems to follow a pattern as follows: -- xfer data -- wait 200 us -- xfer data -- wait 1 ms -- xfer data -- wait 200 us -- xfer data -- wait 1 ms --xfer data -- wait 200 us -- ... Another quirk I seem to have is that if I pulse the ATTN line at some random time, I enter the ISR and everything runs smoothly. However, if I pulse the ATTN line just after a transfer ( within a few micro seconds) I enter the ISR for the completion interrupt, but I seem to miss the interrupt from the ATTN line if the transfer was smaller than 3 words!! I have no idea why it works for larger transfers and not for small transfers... Further if I examine the saved CSR value after an ATTN pulse was sent, I should see th ATTN bit latched, but it is not! can anyone explain this? I tried 2 cards and they both do the same thing. Anyway, any help at all would be appreciated... Eric Everton Avionics Simulation Specialist Dept. 49 Eric.Everton(a)cae.com (450) 476-4484