Re:8088 Domination Post-Mortem, Part 1
by Intermernet on Friday June 20, 2014 @09:54AM
(#7920680)
Your clocking trick is exactly what I spent 3 weeks swapping CPU / MB combos trying to avoid!
Kudos for actually doing it, and making it work!
Oh trust me if I had had the money I would have happily pursued your route. Cutting a trace on your only working computer and soldering bits & pieces onto the motherboard in order to land a job (talk about risk/reward here, I'm not sure how I would have worked without that machine but I really wanted that engine ;) ) made me pretty nervous. If I could have saved myself that batch of cold sweat I would have happily done so.
What got me is that it did work, I fully expected there to be some level of synchronization between the chips that would require both of them to be clocked at the same rate. The only reason I tried this is that the main CPU appeared to stop working and I figured it was worth a shot to see if the FP could go faster. And it did, and not just a little bit faster! Apparently Intel engineers were quite friendly when they designed the interaction between the two processors because in spite of the huge discrepancy in clock speed between the two chips it worked incredibly well.
The Tseng vesa cards did not do 3D but they were blisteringly fast (for the time) if you knew how to hit them 'just so'. Do everything by the row and avoid bank switches at all cost.
The funny thing is that the driver I wrote for the card was only about 2% or so Tseng specific. gp_wdot, gp_rdot, gp_wrow and gp_rrow were the only routines out of about a 150 or so that were optimized and they were quite short to begin with. And that alone was enough to get very close to maximum bandwidth between the CPU and the graphics memory (this was across the VLB).
I like your clocking trick a lot better than mine, I just soldered an extra socket for an oscillator to the motherbord and ran one wire under the chip to the right pin (and I cut one trace on the motherbord). Plugging in a bunch of oscillators until the FP chip started to behave weird (and then adding a little fan and pushing it some more :) ).
Interesting how those payments worked out.
Now I'm seriously wondering if there is a way in which I could resurrect that demo. No idea what I did with the data, I probably still have the code in some form or a descendant of it.
This was the card I originally wrote the code for:
http://www.vgamuseum.info/index.php/component/content/articl...
But by then I may have upgraded to a et4000 (the 3000 was 16 bit ISA).