@Kay K.M.Mods and several other people who have installed Bolle's clone of the
Carrera040 have discovered that there are audio glitches on the SE/30, but apparently not on other Macs like the IIci, when the 040 on the accelerator is being used. I guess it must be a similar problem to what you described.
Could be. I can investigate in the future if we do an SE/30 accelerator.
QUESTION: Why allow switching between 20MHz and 25MHz? Why not just make it a fixed 25MHz? There obviously must be a reason for the 20MHz setting, right?
Yes, the reason is that the 68HC000 was only ever officially specified for 20 MHz operation. 25 MHz is technically "overclocked." However it is widely understood that nearly all 'HC000s (especially later mask revisions) are capable of 30 MHz and faster speeds. I am sure that all WarpSE units will work at 25 MHz but if you are not so confident, you can reduce the speed to 20 MHz using the DIP switch. Interestingly, the WarpSE chipset doesn't support arbitrarily low clock speeds for the accelerated processor. 20 MHz is near the minimum. If you decrease the clock speed below something like 18 or 19 MHz (can't remember the exact figure), there will be a certain race condition and the bus bridge between the fast and slow buses will exhibit random failures. So you can't run at 16 MHz, for example. Around 20 MHz is the practical minimum.
I had the understanding that in addition to the SWIM chip, you must also have the newer 342-0701, HI ROM & 342-0702, LO ROM too, otherwise, with the new SWIM chip and the older 342-0352-A, HI ROM & 342-0353-A, LO ROM, you only get 800K floppy compatibility, even with a 1.44MB floppy drive mechanism.
Yes but we are reproducing the "FDHD" ROM in the "fast ROM" flash chips on the WarpSE, so all you need is the SWIM chip and FDHD drive.
@alxlab has verified that the newer ROM works even with an older IWM chip or an 800k drive. Of course if you switch the DIP switch to the "motherboard ROM" position, you will be using whatever ROM is in your Mac SE's motherboard, in which case you need to have the FDHD ROM on your SE's motherboard in order to use 1.44M disks. The "motherboard ROM" setting is mainly for if you manage to corrupt the fast ROM chips as using motherboard ROM severely reduces performance. The fast ROM flash chips are protected from accidental erasure by a coded command sequence that must be input before an erase/write command can be executed, but it is possible to purposely reprogram them using (for example) BMoW's reflash tool for the Mac ROMinator. If something went wrong during the reprogramming process, the WarpSE would be bricked without the motherboard ROM setting. With the setting you can boot up using motherboard ROM and use a utility program to reflash the fast ROM and fix the accelerator.
Oh also
@JDW, since you did not read the entire thread, maybe you didn't catch what I consider to be one of the the key feature of the accelerator--the
longword posted write buffer. This is a feature of the interface between the 20/25 MHz accelerated CPU bus and the slower 7.8336 MHz bus on the SE's motherboard. Without it, the accelerated CPU would have to slow down to 7.8336 MHz when writing to the screen framebuffer memory. Instead, the posted write buffer allows the fast CPU to "post" two words of data (2 bytes) up to twice in a row with zero wait states (i.e. at full speed). After doing so, the fast CPU can go on executing from fast RAM or ROM while the posted write data is trickled out to the slower 7.8336 MHz bus. And of course all of RAM and ROM are cached on the card, as opposed to other accelerators which cache just a subset of main memory.