Thanks Garrett. I have my NMI button ready to go. The Gazelle is a non-PC compatible without byte-addressable video (character TTY only) so many debuggers won't work because of the graphics. It's such a hassle finding stuff that works on this machine because of the video limitations. Rich -- Rich Cini http://www.classiccmp.org/cini http://www.classiccmp.org/altair32 On 6/10/20, 7:46 PM, "Garrett Nievin" <gnievin@silvaire.org> wrote: Programming the strange "high res" adapter (two full-length boards with a jumper cable, something like 640x400x16) on my Sperry PC back in the day, I just soldered in a switch that connected NMI to ground and used it with basic tools like Borland Turbo Debugger. http://www.bitsavers.org/pdf/borland/turbo_assembler/Turbo_Debugger_2.0_User... I'd be running graphics code on the "high res" adapter, and have an MDA card with debugger running on the monochrome display. Cheers, Garrett On Wed, 10 Jun 2020 19:13:14 -0400 Richard Cini via vcf-midatlantic <vcf-midatlantic@lists.vcfed.org> wrote: > All – > > > > I’m working on an S100 project with my Gazelle (a VGA board) which is based on a standard Trident VGA chip. The BIOS on the video board relies on a PC BIOS (which doesn’t exist for the Gazelle) so I’ve had to hack something together for it to make it work. The BIOS is barfing somewhere in the initialization, but it’s a hard crash so resetting it to regain control destroys the context. I’m running under MSDOS 2.01. > > > > I remember that there were debuggers like Periscope or SoftICE that could trap NMI, but I need it to be pure character-based like MS-DOS debug. Does anyone know of any debuggers like this? There was one by Paul Vojta, which I have the code for, but that doesn’t trap NMI. I wonder if I could just have the NMI call INT 03H (debug break) since they all trap that. > > > > Any thoughts or help appreciated. Thanks! > > > > Rich > > > > -- > > Rich Cini > > http://www.classiccmp.org/cini > > http://www.classiccmp.org/altair32 > > >