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Message ID: 270     Entry time: 11 Jul 2006
Author: Razvan Stefan Gornea 
Topic: Forum 
Subject: Tundra Universe CA91C042 
I am not using Midas but I need some help from somebody experienced with VME access using the Tundra Universe, so I thought here I have a chance ...

I have a GE Fanuc 7700 and use the vme_universe driver (ver. 3.3). In the past I programed for a DAQ board using A24/D16. Now I have a new board using A24/MB and I am really last!

So the board has some 64-bit registers and some 32-bit registers (all aligned on 64-bit) and a FIFO to read the main data. After reading the user manual for universe chip and the docs for the driver I am still confused about how things are supposed to work.

First my understanding is that for reading 64-bit I need anyway the multiplex block mode. But nowhere I could find if the multiplex mode supports 32-bit transfers. Should I map two windows on the same VME address range, one for A24/D32 and one for A24/MB? Or read everything with an unsigned long long and cast to unsigned int all 32-bit registers?

Second I don't know how to handle the FIFO which is in the middle of the address range. When the board has a trigger I have to read more than 100000 times this FIFO. If I simply read at the FIFO address 100000 times do I get the VME multiplex block mode (if the window has been mapped with A24/MB address modifier)? How does the chip/driver know not to send the address and just do the data cycle after the first read?

I also had the naive idea to have a master window mapped on the board address range to access all the registers except the FIFO and to create a DMA buffer for the FIFO (FIFO readout is where most of the work is anyway so I guess an advantage is that will free the CPU) but it seems to me that the dma_transfer function in the kernel module increments the address. I don't dare change this since I don't even understand the exact relationship between accesses to the mapped window and what's happening on the VME bus.

Thanks for any help!
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