From: "Aley Keprt" <[EMAIL PROTECTED]> > Although I don't understand how does it work, I'm sure that we are facing a > very terrible > computer design, which has underdimensed system bus, resulting in a large > speed loss (upto > 32%). This is similar to modern PC computers with Pentium 3 running at > 1000MHz, and bus > running at 100MHz. I think the best solution on Sam would be circuitry with > a separated > 64KB videoram and 512KB other ram, where CPU would run at its 6MHz. Then, > when emulating > ZXS on Sam, we would put all this stuff into videoram, so the CPU would be > regularly > slowered to make ZXS emulation better (although still not perfect).
Tell ya what. If you build it - in silicon - I'll consider buying one. Look Aley, It's a 13/14 year old design. It was great for its time. But there were trade offs. There always are. The fact that *to you* it looks like a crazy design today doesn't take into account those trade offs. If you want to know the real reason for the weirdness of the timing of the ASIC on the SAM, look into CAS/RAS burst reads (the SAM loads as much of a line at a time into memory as it can, to reduce contention, IIRC). There's only so much it can do at times, and the amount of time needed to wait for the CAS/RAS cycle to complete is what determines the speed of the system. If it's in the middle of a read, the SAM will be halted until the read completes - and will then be given the chance to do something. But not much, because the ASIC has to take control of the cycle again soon. As for Mode 1 timing, the SAM is deliberately slowed down in Mode 1. Simon (running a 1.4Ghz AMD T-bird with 0.5Gb of RAM these days... and not noticing any memory contention at all)
