mkarcher wrote on 2023-03-04, 18:14:
GigAHerZ wrote on 2023-03-04, 12:55:
Any good tool that would reliably test if the L1 (and why not also L2) cache actually works properly in write-back mode? Any good experience with some tool?
You could use Heise's "ctcm" utitility (c't Cache Measurement), made by the german IT magazine "c't". An official download link is ftp://ftp.heise.de/pub/ct/ctsi/ctcm17a.zip , on a 486 computer that version should be invoked with "/NOP" to prevent a crash. In most cases, this utility can correctly identify the cache mode, and whether a write-back L2 cache runs in "always dirty" mode or in a proper configuration.
I've tried this, 1.5, 1.6 and 1.7 and it seems to show complete BS when you have 1024kB of L2 cache.
1.5 says there is no L2 cache.
1.6 and 1.7 say that there's 2048kB of cache and everything is in write-through mode. (Thanks for the /nop hint!)
But i've modified the bios ( QDI V4S471/G locks up with 1024kB of cache [Fixed! Nicer Award BIOS available!] ) and i'm absolutely sure that at least L2 cache is in write-back mode.
EDIT:
But thanks to this thread, i started tracing the tracks on the motherboard and this is the information about my QDI board. ( https://theretroweb.com/motherboards/s/qdi-v4s471-g )
JP44: Multiplier. 1-2=4x, 2-3=3x
JP18: DACK1. 1-2=Pull-down, 2-3=Pull-up
JP19: DACK0. 1-2=Pull-down, 2-3=Pull-up
J14: pull-down CPU B13 "WB/WT"
J11: pull-up CPU B13 "WB/WT"
J12-1: CPU B12 "Cache"
JP29-2: CPU A12 "HITM"
JP28-1 = pull-up
JP28-2 = CPU A10 "INV"
JP28-3 = CHIPSET 104 "W/R"
JP8-2: CHIPSET 118 "PCD"
This thread has a lot of good information. Thank you! I'm tracing that information all back to my board and hopefully i'm going to have a blazing fast 1MB L2 cache equipped 486. 😀
EDIT2: I think i got everything working now. The L1 cache speed jumped from ~89MB/s to ~129MB/s. Love it.
NB! The CTCM 1.6 and 1.7 claim that i have 2048kB of L2 cache and both L1 and L2 work in write-through mode. CTCM 1.5 doesn't recognize L2 cache at all, but at least claims that L1 is working in write-back mode.
Am i correct that L1 WB can be "detected" by seeing higher "copy" speed in speedsys than the "read" speed is? Is it always the case or am i "special"?
"640K ought to be enough for anybody." - And i intend to get every last bit out of it even after loading every damn driver!