Very minor: I've added Enterprise emulation to the emulator that I write, Clock Signal, for macOS and other Unixes.
GitHub;
macOS binary releases;
Linux binary releases via Snapcraft.
On macOS it's a fully-native, signed application using Metal and the native UI. Elsewhere it is available both as a Qt GUI application and as an SDL build that's more useful for command-line invocation and for file associations.
Probably its most interesting feature is that it can simulate composite video by generating and then decoding the actual composite video stream. No post hoc blur-it-up-a-bit filters here. It also does audio by sampling internally at a sensible native rate for the emulated machine and then low-pass filtering down to whatever your host machine can output. So e.g. on any garden-variety Mac from the last decade or so you can listen to your Enterprise at 96 kHz.
That all being said, Enterprise support is very provisional and known to be imperfect. So tolerate it only as far as you can.
Specifically:
- it supports IMG files only, there's presently no other way to load software; and
- something is definitely off in terms of timing.
Notable software issues of which I'm aware include the conversion of the CPC version of Chase HQ playing its sampled sound (like 'Let's go, Mr Driver!' way too quickly, but then weirdly slowing way down every time it would make a sound effect that the Spectrum would use its toggle speaker for; and SIDBASIC reporting a 3MHz CPU And then just not playing any audio. Like, no Dave writes at all, not like I'm processing the audio incorrectly.
Any other feedback would be greatly appreciated. Some screenshots are attached. Alternatively,
here it is on YouTube.
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Some random technical details, in case they're interesting:
In this implementation Nick runs 40434603/11360000ths as fast as the CPU, which is currently always 4Mhz. So I've clocked Nick at around 14.2375Mhz.
If the Z80 performs a Nick access it must wait to start the final clock cycle of its machine cycle until it is in the first two Nick cycles of the six-cycle block allocated for Z80 access. I should read mode on this. I observed that the entire six-cycle window is only around 1.68 Z80 cycles long, but of course the Z80 is paused in half-cycle increments so the maximum it could depend upon getting is 1.18 cycles of clear space. Hence fitting the final cycle into that window.
Nick's interrupt output is adjusted immediately after reading that byte of the mode line.
I wasn't clear on the correct way to transition between noise polynomials on Dave, so that's probably inaccurate. But the LFSRs all use IstvanV's documented polynomials, at least.
lgb.hu mentions that "There is some odd behaviour that you can read the (Nick's) bus state on these I/O ports. In theory it can be used for some video effects. I can't say I can understand that very well though
"; through a lack of further information reads from my Dave return the last byte fetched, if any, otherwise 0xff. That's permitting for the fact that I haven't read up on how the refresh addresses are generated though.
As per my reading of the documentation, column 10 is the first one output in composite mode. The colour burst covers columns 8 and 9. Output starts at column 8 in RGB mode, even on lines in which a mode line isn't read.
There's a simulated spinning platter for disks, so floppy access should be approximately real time.
Because the simulated CRT runs a couple of phase-locked loops to track discriminated syncs, you'll get some screen bouncing during phase-breaking display transitions.
It's likely I'll add tape image support before figuring out a way to bridge to the local filing system, though for the latter I'm thinking of maybe implementing an IDE drive and mapping FAT back and forth. That'd be more reusable with other machines I implement, e.g. the MSX and Atari ST both also use FAT12 and FAT16.
I forgot I hadn't yet implemented the 8/12MHz Dave divider. It'll be in the next release. I don't think it factors into any of the known incompatibilities.
