DR11-W to Model-1/20 on 4.1 BSD

[PAD Powell [Admin]]

The first thing you should do is take the far end of the device off,
and put a loop-back cable on. This can be done by using a single ttl
gate, 74ls00, with the data/out strobe being buffered and drive the acknowledge.
Ask your local hardware type to whip this up, should take about 3 minutes,
if you are crude, and vulgar.  Now, tie a monostable onto the fool thing,
to generate a pulse (drive an LED) each time you get a data transfer.
If you put a counter on the end of it, you can also get a count of the
number of pulses.  

Now, you are in shape to debug your driver.   Work on DMA out first,
then work on DMA in.  If you are clever, your hardware guy will hook up
a couple of counters to the input signals.  Now you can do most of the
debugging.

Warning:
	Most of the times you hang is cause you are sending the wrong
number of bytes to the destination.  Read the documentation on the
value to be loaded into the Byte/Word Count register carefully.
MAKE DAMN SURE YOU HAVE NOT GOT SIGNED/UNSIGNED arithmetic problems.
Finally,  are you sure that you loaded the register?  Check the compilation
assembly for the instructions,  and make sure you are loading with the
right register.

Patrick ("I hates DMA Devices forever") Powell