18 Jul
2010
18 Jul
'10
9:19 a.m.
From: "Chris M" <chrism3667 at yahoo.com>
Sent: Saturday, July 17, 2010 8:37 PM
To: "General Discussion: On-Topic and Off-Topic Posts"
<cctalk at classiccmp.org>
Subject: Re: 68K (ISA) project
Oh, we agree! With "building" I only meant the soldering job. Writing
firmware from scratch can be tedious, I know, been there!
My first 68k design did not work for over 4 weeks until I soldered a "tool"
to see the state of several pins of the 68k at the same time.
Back then I only had a 2 channel scope, which were few channels short :-)
The mistake was fairly simple (always is when you know it). As coming from
8-bit 6800/6809, I initialized the stackpointer A7 to the highest RAM
address. The firmware did work up till the first BSR. Yeah, the stackpointer
must be on an even address ...
Starting with a real 68k is easy. I agree that FPGA programming has a steep
learning curve.
I started several times, but never really got through it. Too easily
distracted to other "easier" projects, but one day I will get a good start
at FPGA stuff.
- Henk.
On 15 Jul 2010 at 19:08, Henk Gooijen
wrote:
I sort of beg to differ. Writing competent firmware doesn't seem to be
such an easy task. Sure building a small board w/ultra minimal firmware
shouldn't be too bad, even the designing part. But I've been eyeing this
Robot Brain (80188 based) board in Radio Electronics, and I doubt that too
many people on this list would have the skill to design that from the
ground up (I imagine there are exceptions though). I do have the artwork
and most or all of the firmware, so I am going to build one. Soon...
Most people will simply want to copy something from a textbook or
magazine. If anyone wanted to develop something useful, a FPGA replacement
for some unobtainium chip or whatever makes much more sense to me. And
even that is something of a steep learning curve. Building an SBC (for any "old"
processor) is not too
difficult ... the question is *what* are you planning to do
with it? Do you have a purpose? Building just for the
"building" is not very long lasting ...