5 Feb
2024
5 Feb
'24
4:03 p.m.
On Mon, 5 Feb 2024 19:16:46 -0000
"Rob Jarratt" <robert.jarratt(a)ntlworld.com> wrote:
Your annotated VT100 listing was invaluable in helping
me to fix my
own VT100 (still not working though, but on the video output side).
Would be interested in how you did it, I get the impression from your
message that you used an emulator to observe the behaviour?
The main write-up on that is here:
https://vt100.net/dec/vt100/rom/how
(which I am always prepared to revise, if something doesn't make sense!)
I started with MAME, because it supports VT100 emulation with the
exception of smooth scrolling, and because it has a really excellent
debugger. However, I had to switch to my own program based on Nicolas
Allemand's 8080 core in the end, for two reasons:
1. I needed to stimulate the terminal with serial inputs and key
presses and observe the serial outputs, and
2. I needed to know that I had covered the entire ROM, so I combined
the 8080 core with a coverage checker, to mark all reads, writes
and DMA accesses to RAM while it worked its way through a file that
contained stimulation instructions: "pause", "keyboard character",
"serial input", etc. Coverage checking might sound bizarre, but I had
some code that I disassembled, understood and documented and could not
for the life of me work out why I couldn't provoke it into executing;
it turned out to be a bug in the firmware.
Regards,
Paul