[Gb-ccb] FPGA design

[John Ford]

This is great.  Note that we only want to be able to read back the
configuration on demand, say if things don't seem right.  Not
necessarily in real-time all the time.  A command in the interface
software library, say, get_configuration_registers(), would return the
current values in the registers in an array.  Or whatever.

John

Martin Shepherd writes:
 > On second thoughts, I think that I see a way to readback the
 > configuration registers without disturbing the asynchronous interrupt
 > mask readback, so I guess I'll do it tvia the EPP port after all. EPP
 > hardware supports both data reads and address reads, using different
 > strobe lines for the two modes. So, if I use data reads to read back
 > the currently addressed configuration register, and address reads to
 > read the interrupt mask, then this will avoid the race condition that
 > was worrying me, and I will still be able to read the interrupt mask
 > from an interrupt handler, without having to use an extra write to say
 > that this is what I want the FPGA to send me, and without the danger
 > of breaking up the sequence of single byte reads needed to readback
 > the configuration registers.
 > 
 > So, in other words, please ignore my previous explanation of why I
 > didn't want to do this, and instead assume that I will add readback
 > via the parallel port, as requested.
 > 
 > Martin
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