Reply 120 of 167, by feipoa
My Cyrix Sx486SLC2-50MP finally arrived. It took about 7 weeks, but looks to be original product.
I desoldered the SXLC2-40 and soldered on the SLC2-50.
The SLC2 is indeed default in 2x mode. I ran it at 66.6 MHz. With all of L1's cache region set as non-cacheable, chkcpu shows the speed as 61 MHz. With the cache region inhibited, e.g. with cyrix.exe -i1, chkcpu reports 33 MHz. Obviously, chkcpu is mistaken in both situations. Nonetheless, the SLC2-50 works fine at 66.6 MHz, but it needs active cooling. Without a heatsink and fan at 66 MHz, the system will hang up once the CPU reaches around 60 C. So I will need to figure out some kind of solution that isn't unsightly.
Here's some numbers at 66.6 MHz with an ET4000AX.
Landmark v2: 166 MHz ALU and 45.3 MHz FPU
Cachechk: L1 = 44.3 MB/s and RAM = 11.5 MB/s
3Dbench = 18.1 fps
DOOM = 10389 realtics, or 7.19 fps
The system definitely feels chipper. Note that the FSB = CRYSTAL / 4, so FSB = 66.66 / 4 = 16.7 MHz. The Evergreen unit has a custom 2x PLL, making it 33.3 MHz, and the SLC2 has another 2x PLL, making the CPU run at 66.6 MHz. Is the ISA frequency the same as the FSB on these 286 boards, meaning that the ISA bus is running at 16.7 MHz? If so, can the Adaptec AHA-1542CP cope?
By way of comparison, when I had the SLC-33 soldered on, I recorded:
Landmark v2: 105 MHz ALU and 41.6 MHz FPU
Cachechk: L1 = 25.1 MB/s and RAM = 11.5 MB/s
3Dbench = 14.2 fps
DOOM = 12609 realtics, or 5.92 fps
I then tried to run the SLC2-50 at 70 MHz, but I was noticing some characters on the screen that should not be there, so I assume 66.6 Mhz is a realistic maximum speed.
The other configuration I wanted to try was an overclocked SLC33. If the SLC25 can only do 33 MHz reliably, then I figure the SLC33 can only do 40 MHz. This would give a 20 Mhz FSB compared to the SLC66's 16.7 MHz, but I doubt would make for a faster system. Now if the SLC33 could run at 45 or 50 MHz MHz, it would probably be faster overall than the SLC66. Unfortunately, the effort and risk required to solder/desolder these QFP chips is the limiting factor for me and I won't be experimenting further in this capacity. If I had another Evergreen 486 SuperChip, I'd be more willing to experiment further as I have three NOS SLC33 chips.