pc104 ISA bus-mastering & custom hardware

[Paul Miller]

I've been thinking about fabricating my own hardware for a pc104 board 
that uses a 16-bit ISA bus.  Basically, I want to interface a DSP 
such that it has access to the pc104's shared memory.  I'm fairly 
confident that I can work out the circuit design, but I need to know 
more about Linux's ISA support.

1) What is needed to support ISA bus-mastering?  I would like the ISA 
device to write directly to the pc104's shared memory.

2) What memory regions can I write to?  Am I limited to <16MB or is it 
more restrictive?  64K-1MB, 15-16MB?

3) How can I reserve a specific memory region?  How much memory can I 
use?  I plan to have a way to communicate to the DSP (via I/O) what 
memory address to access.

4) How do I enable a 16-bit DMA channel?  Do I need to do anything 
beyond enabling DMA?

5) What are some good examples?

6) What else should I be thinking about?

Thanks!
-Paul
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