Alan wrote:

>The book "PA-RISC 2.0 Architecture" by Gerry Kane is about 550 pages
>long and describes the instruction set very well.  It presents the
>details of the memory addressing, fault handling, and privilege
>management, plus a good bit of other stuff.  The total information
>that it presents about the I/O system is four paragraphs *in the
>overview*!  A distillation of the information in those four paragraphs
>is:  I/O is memory mapped, it can use DMA, and it can cause interrupts.

This is probably also the same issue that the PA-RISC Linux folks
have been suffering from (and maybe are still suffering from). There
is a lot of low-level documentation on proprietary hardware that is
probably not publicly available.

As far as I understand, the PA-RISC Linux people are providing a
working implementation for recent hardware, like A-class systems,
where documentation for driver writes is available...

This situation might make it easier to write a platform emulator
that emulates an A-class machine's hardware (compared to emulating
a simpler hardware like 3000/9x7 or somesuch; oops, I notice that
I am just assuming that older hardware might be easier to emulate
because of less complex CPU (32bit versus 64bit) and so on).

On the other hand, an "A class PA-RISC platform emulator" would
limit the MPE/iX operating system releases that can be run on it.

Lars.