Q-bus to CF

[Johnny Billquist]

"Bob Armstrong" <bob at jfcl.com> skrev:
> 
>> Sridhar Ayengar (ploopster at gmail.com) wrote:
> 
>> Or if you're willing to write an MSCP layer into your controller firmware.
> 
>   I actually think this is the "right" way to solve the problem in the case
> of the PDP-11 and VAX, but then controller is no longer a simple device.

I'd say it would definitely be the right way.

What people seem to forget (or ignore) is that unless you decide to emulate an 
existing DEC device, you not only need to write a device driver for the OS, 
which sure is some work, but doable.
But you also need to write some bootstrap code, which needs to be placed in a 
rom. That will quickly get a bit more ugly...

There is a big difference to a PDP-8, which this has been compared to up until 
now. The PDP-8 is really simple in design, and so is booting one, usually.

A PDP-11 is way more complex to boot. Not only do you need the initial boot 
code, in the boot ROM. You then also need the bootstrap for the OS, which 
resides on disk. I don't know about RT-11, but for RSX, this is a separate piece 
of a driver which in no way is related to the device driver that you use once 
the system is booted. And this piece is tightly integrated with the OS and is 
embedded deep inside stuff.

So, unless you want a disk that you can't boot from, you have a big chunk of 
work to get it working.
So doing an emulation of an existing device makes much more sense.
And of all the existing devices, MSCP is by far the best choice when picking 
something to map to modern hardware.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol