Very interesting discovery about how to use two BIOS images on one EEPROM w/M912. I think my version of the MB already has the DIP-32 socket.
With respect to the J.2 AWARD BIOS...
Back in February, I started testing with the original PC Chips m912 v1.7 BIOS from 12/02/1994. This BIOS works out of the box with:
8 GB CF card w/LFB, 32-bit
Intel DX4 WB
does not work with Am5x86, even in 3x (blank screen)
With Intel DX4-100-WB, and without loading any other DOS drivers, I record 3376 KB/s for a 64 Kbyte tranfers in DOS.
With the J.2 BIOS, also using the Intel DX4-100-WB, I record 2476 KB/s for the same CF card. I've got block mode enabled in the AWARD BIOS, but there aren't any other speed settings. I am guessing that the IDE transfer rate is being put in PIO-1 or PIO-2, or 32-bit transfers aren't being used. I have the VLB I/O card setup for the fastest speed via the jumpers. There aren't any BIOS settings for IDE speed or 32-bit mode.
I compared cachechk timings to ensure the original AMIBIOS and AWARD BIOS were onpar w.r.t. L1, L2, RAM speeds, and they are.
M912 J.2. with Am5x86-133 and Cx5x86-133 run fine. However, on the pre-POST boot screen, the Am5x86-133 shows up as Enhanced Am486DX4-S at 100MHz, while the Cyrix shows up as Cx5x86-S CPU at 132 MHz. However, CHKCPU reports 133 MHz and Write-Back enabled. 8 GB CF card detects and boots fine. No issue with fake cache or incorrect cache being displayed after POST. However, IDE speed is abnormally slow at 2415 KB/s.
Both CPUs are able to run DOS benchmarks.
I then tested the AMI 1995X BIOS. Am5x86-133 and Cx5x86-133 work fine and report correctly. 8 GB CF card detects and boots fine. No issue with fake cache or incorrect cache being displayed after POST. IDE speed OK at 3376 KB/s.
Curiously, with both AMI BIOSes (original and 1995X), the IDE read speed is abnormally low only when using a Cyrix 5x86. Coretest reports 1852 KB/s, whereas with the Am5x86-133, it reports 3376 KB/s. The AWARD J.2 BIOS shows even lower with the Cyrix 5x86-133 installed, at ~1400 KB/s.
What I found most troubling was the Cyrix 5x86 massive IDE slow down. While this can probably be circumvented by using a SCSI card, it is a serious limitation.
I think Jan wanted to find solutions to these issues before releasing his BIOS. There's the Am5x86 IDE slow down speed compared to the AMIBIOS; there's the additional Cyrix 5x86 IDE speed slow down (worse than AMD 5x86 at the same core frequency); there's the POST screen mis-identification of the Am5x86 CPU as Am486DX4-100.
Plan your life wisely, you'll be dead before you know it.