Added: Oct 12, 2008
From: 80Thom80
Duration: 0:22
This shows how my 3d code currently looks. Multiple objects and multiple colours abound. And the frame rate is starting to drop. There's some bug in reverse face removal which I'm going to have to take time out to fix before I can do a more thorough stress test. However, I felt that this was enough to distinguish my code from cheap demo effects. The code is now formulated as an open library for 3d graphics, designed around an easy interface for third parties. For the purposes of exposition: the Sam Coupé is a z80-based computer from the late 1980s. It boasts a 256×192, 16 colour display and a processor that, in real terms, runs at about 4 Mhz. My code could probably be adapted to any z80 platform.
Channel: Tech
Tags: 3d 8bit assembly computer coupe coupé demo graphics homebrew library sam spectrum vector z80 zx
Rating: ( ratings) Views: 81 Comments: 6
80Thom80 Says:
Oct 12, 2008 - Well I didn't actually do the maths. I just took the well-worn rubric that "the Sam goes about 14% faster than the Spectrum" and multiplied 3.56 by 1.14. Which gives a shade over 4.
QuazarSamCoupe Says:
Oct 12, 2008 - I've never the SAM being quoted as just 14% faster! Although, popping the SAM into graphics MODE 1 does add extra contention to the memory to slow the SAM down to around 4MHz to allow ZX Spectrum emulators get a bit of help achieving the right sort of speed instead of being too fast. Could that be what you are thinking of?
80Thom80 Says:
Oct 12, 2008 - Per wikipedia (so admittedly not particularly guaranteed to be accurate): "Internal RAM was shared between the video circuitry and the CPU, with CPU accesses incurring a speed penalty (the memory contention delay) as it waited for ASIC accesses to finish. As a result, the SAM Coupé's CPU ran only around 14% faster than the ZX Spectrum CPU". I think I've contributed to that article about four times and feel like it wasn't my original source for that belief, but I don't think I wrote that bit.
QuazarSamCoupe Says:
Oct 27, 2008 - Hmmm! My last reply didnt appear! Anyway, seems like a bit of inaccuracy on wiki! 14%... nope - the SAM is faster! The SAM's CPU is always clocked at 6MHz, but with the contention on the memory when the ASIC is fetching bytes for the display the 'effective' speed is around 4.8MHz, or when in MODE 1 (to emulate Speccy graphics) it's more around 4MHz due to additional /wait delays added to slow the CPU down to get closer to the slower speed of the Speccy.
QuazarSamCoupe Says:
Oct 27, 2008 - Plus, some of the memory on the actual Speccy is contended too, so the Spectrum will have an effective speed slower than the true 3.25MHz or whatever clock speed. With the Mayhem Accelerator on the SAM there is no contention on memory reading, which also makes a dramatic speed boost even if still at 6MHz. At the (current) top speed of 20MHz benchmarks show it's a whopping 486% faster than the normal SAM speed (even though it's only a 333% increase in clock speed)
QuazarSamCoupe Says:
Oct 12, 2008 - With the 6MHz Z80 having to wait to access memory while the video hardware is building up the screen display the effective speed is more around 4.8MHz. Although, the SAM has been pushed ^above^ 20MHz now by myself... ;)