Search found 84 matches

by scarybeasts
Sat May 25, 2019 7:11 am
Forum: general
Topic: Remarkable videos recently posted on Youtube
Replies: 231
Views: 25738

Re: Remarkable videos recently posted on Youtube

Great Exile video, nice production and appreciation of the technical brilliance. Thanks for sharing!
by scarybeasts
Mon Apr 22, 2019 2:31 am
Forum: software: classic games
Topic: Interesting Camelot bug
Replies: 3
Views: 285

Re: Interesting Camelot bug

0xC0DE wrote:
Sun Apr 21, 2019 7:34 am
Does this count? Also about key handling in Camelot.


viewtopic.php?f=4&t=16774&view=unread#p232025
Sounds like that's the Electron version; I didn't specify but I'm referring to the BBC version. Looks like Camelot has all-around interesting keyboard quirks :-)
by scarybeasts
Sun Apr 21, 2019 2:36 am
Forum: software: classic games
Topic: Interesting Camelot bug
Replies: 3
Views: 285

Interesting Camelot bug

Hi, While working on a new experimental emulator, I found a bug in Camelot that seemed interesting / unexpected enough to document. It's pretty easy to trigger: on the game start screen (screenshot attached), press space to start but _hold space down_ until the game has started and Sir Camelot is fi...
by scarybeasts
Wed Apr 03, 2019 8:30 pm
Forum: software: classic games
Topic: Who's ready for... guess that game! ;D
Replies: 52
Views: 1482

Re: Who's ready for... guess that game! ;D

Sim? And wasn't that 4 the channel 4 logo from the time?
by scarybeasts
Sat Mar 16, 2019 3:42 am
Forum: software: classic games
Topic: Revs special edition?
Replies: 1
Views: 297

Revs special edition?

Hey,

Fairly random question but does anyone else remember a "Revs special edition" where the boxed game came with some little formula 3 toy racing cars?


Cheers
Chris
by scarybeasts
Fri Feb 01, 2019 3:38 am
Forum: emulators
Topic: VIA test case: T2 freeze vs. IRQ
Replies: 2
Views: 232

Re: VIA test case: T2 freeze vs. IRQ

Hi,

Thanks, yeah I thought the IRQ might still fire. Another crazy corner case but probably not one that's super important to emulate.


Cheers
Chris
by scarybeasts
Thu Jan 31, 2019 9:17 pm
Forum: emulators
Topic: VIA test case: T2 freeze vs. IRQ
Replies: 2
Views: 232

VIA test case: T2 freeze vs. IRQ

Hi, Unburying this minor unresolved test case from another thread. Cheers Chris 10 REM RESULTS FROM JAN 2018 20 DIM MC% 100 30 DIM R% 16 40 P% = MC% 50 [ 60 OPT 3 70 SEI 80 LDA #&40 90 STA &FE4B 100 LDA #&03 110 STA &FE48 120 LDA #&00 130 STA &FE49 140 LDA #&60 150 STA &FE4B 160 LDA &FE4D 170 STA R%...
by scarybeasts
Sun Jan 27, 2019 8:57 am
Forum: emulators
Topic: Two more VIA test cases
Replies: 3
Views: 328

Re: Two more VIA test cases

Thanks! VIA.T12 is about as expected but VIA.T23 is interesting, it appears timer freezing or continuing takes effect one VIA tick later than you'd expect. This does suggest the follow-up test appended below: if the "one VIA tick later" is actually T2 reload, does the IRQ fire or not? Cheers Chris 1...
by scarybeasts
Sat Jan 26, 2019 12:19 pm
Forum: emulators
Topic: Two more VIA test cases
Replies: 3
Views: 328

Two more VIA test cases

Hi, Still plugging away trying to get to all the 6522 corner cases for core functionality:-) Finally running low on corner case ideas but here's what has come to mind. The second one could be particularly interesting -- it's writing the T1 latch values at the same time the timer is relatching. As al...
by scarybeasts
Thu Jan 17, 2019 3:28 pm
Forum: emulators
Topic: System VIA T2 value on a real MOS1.2 beeb?
Replies: 2
Views: 247

Re: System VIA T2 value on a real MOS1.2 beeb?

Thanks. Power-on counter value is effectively random then.
BigEd wrote:
Thu Jan 17, 2019 9:29 am
First try:

Code: Select all

>PRINT ~?&FE49
        55
>PRINT ~?&FE48
        AE
Second try: 69 and 0.
Third try: 58 and F6
by scarybeasts
Thu Jan 17, 2019 9:23 am
Forum: emulators
Topic: System VIA T2 value on a real MOS1.2 beeb?
Replies: 2
Views: 247

System VIA T2 value on a real MOS1.2 beeb?

Hi, TL;DR -- what do the following peeks give on a real BBC B (MOS1.2, vanilla?) on a fresh power-on? Are the values stable across a few tries? PRINT ~?&FE49 PRINT ~?&FE48 It's interesting because MOS1.2 freezes the system VIA timer 2 some short and constant time into initialization. Reading these v...
by scarybeasts
Sat Jan 05, 2019 8:59 pm
Forum: emulators
Topic: 6522 VIA emulation: ACR writes vs. timer expiry
Replies: 12
Views: 602

Re: 6522 VIA emulation: ACR writes vs. timer expiry

I don't know anything about this, but could there be a pipeline delay? Does writing to ACR once cycle before expiry affect the IRQ in a more understandable way? Or maybe that's already been well covered? One of the tests in the most recent dump did the same ACR writes one cycle before IRQ (the coun...
by scarybeasts
Sat Jan 05, 2019 8:57 pm
Forum: emulators
Topic: 6522 VIA emulation: ACR writes vs. timer expiry
Replies: 12
Views: 602

Re: 6522 VIA emulation: ACR writes vs. timer expiry

it is strange to think what could be going on in the silicon to make ACR 00 -> 40 at IRQ time asymmetric with ACR 40 -> 00 at IRQ time. As has been remarked before, it's only "strange" if you assume that everything is synchronous (clocked). For somebody like me who, back in the 1970s and 80s, desig...
by scarybeasts
Sat Jan 05, 2019 11:47 am
Forum: emulators
Topic: 6522 VIA emulation: ACR writes vs. timer expiry
Replies: 12
Views: 602

Re: 6522 VIA emulation: ACR writes vs. timer expiry

Here you go: Thanks BigEd. This confirms the quirky result with no additional quirks uncovered. This is easy enough to emulate but it is strange to think what could be going on in the silicon to make ACR 00 -> 40 at IRQ time asymmetric with ACR 40 -> 00 at IRQ time. In both cases, ACR==00 wins; the...
by scarybeasts
Fri Jan 04, 2019 10:52 am
Forum: emulators
Topic: 6522 VIA emulation: ACR writes vs. timer expiry
Replies: 12
Views: 602

Re: 6522 VIA emulation: ACR writes vs. timer expiry

Here you go: Ok, here's my (final?) attempt to shed light on the weird asymmetric behavior of ACR write vs. timer interrupt. These two test cases are kind of behemoths now (VIA.AC6, VIA.AC7) but if BigEd or some other kind soul ran these, we might learn a bit more for how emulators should behave in...
by scarybeasts
Thu Jan 03, 2019 10:19 am
Forum: emulators
Topic: Borrow a beeb in the Bay Area?
Replies: 6
Views: 510

Re: Borrow a beeb in the Bay Area?

Kazzie wrote:
Wed Jan 02, 2019 1:23 pm
This might be a silly question, but which bay are you near? Cardiff, Morecambe, San Fransisco, Colwyn, Wemyss...?
Sorry, San Francisco Bay Area, seems like I've been Americanized due to living here too long :-)
by scarybeasts
Wed Jan 02, 2019 8:17 am
Forum: emulators
Topic: 6522 VIA emulation: ACR writes vs. timer expiry
Replies: 12
Views: 602

Re: 6522 VIA emulation: ACR writes vs. timer expiry

Here you go: Thanks! This is as expected. jsbeeb and b-em nail both of those tests (b2 needs to not re-arm the timer on a flip from one-shot to continuous). There must be something timing related going on, or maybe my original test cases had a bug. I'll go away and study them some more. Cheers Chris
by scarybeasts
Wed Jan 02, 2019 6:42 am
Forum: emulators
Topic: 6522 VIA emulation: ACR writes vs. timer expiry
Replies: 12
Views: 602

Re: 6522 VIA emulation: ACR writes vs. timer expiry

On my Beeb, (Rockwell R6522P, datecodes 8243 and 8304) both cases return 0,0 - see below. Hi BigEd, Happy New Year! May it bring lots of beeb tinkering :-) That's definitely an unexpected result but that makes it interesting. None of the emulators return 0,0 for both test cases. Would it be an impo...
by scarybeasts
Mon Dec 31, 2018 11:30 pm
Forum: emulators
Topic: 6522 VIA emulation: ACR writes vs. timer expiry
Replies: 12
Views: 602

6522 VIA emulation: ACR writes vs. timer expiry

Hi, These two cases are interesting, they write to ACR to change the timer from continuous mode to one-shot mode (and visa versa) at the same time the timer is expiring. Except for jsbeeb, the write seems to take effect before the timer fire logic runs. Tests cases are VIA.AC2 and VIA.AC3 in the SSD...
by scarybeasts
Mon Dec 31, 2018 8:21 pm
Forum: emulators
Topic: 6522 VIA emulation: T1LH writes vs. T1 interrupt
Replies: 11
Views: 596

Re: 6522 VIA emulation: T1LH writes vs. T1 interrupt

I think we've already established that I had no idea what I was doing when writing B-em's VIA code. I assume you started from the datasheet? After the discussions about the 6845 previously it does seem that the datasheets only include a level of detail sufficient for people to use the chip for the ...
by scarybeasts
Mon Dec 31, 2018 7:31 pm
Forum: emulators
Topic: 6522 VIA emulation: IFR write vs. timer interrupt
Replies: 8
Views: 353

Re: 6522 VIA emulation: IFR write vs. timer interrupt

This result does kind of have a symmetry with Rich's results though: it seems any time there's a VIA cycle where the timer is firing at the same time as some register write that would tend to cancel the interrupt, the timer firing wins... So that would explain this piece of B-Em code mentioned in t...
by scarybeasts
Mon Dec 31, 2018 6:56 pm
Forum: emulators
Topic: 6522 VIA emulation: PB7 toggling vs. PB7 mode
Replies: 3
Views: 292

Re: 6522 VIA emulation: PB7 toggling vs. PB7 mode

Thanks! Victory to MAME.
by scarybeasts
Mon Dec 31, 2018 9:21 am
Forum: emulators
Topic: 6522 VIA emulation: PB7 toggling vs. PB7 mode
Replies: 3
Views: 292

6522 VIA emulation: PB7 toggling vs. PB7 mode

Hi, Simple test case VIA.PB2 (in attached SSD or pasted below via the magic of *SPOOL and bbcim). Probably not a very significant test case but I mentioned to Tom I'd put it together. MAME is the only emulator that gives 128 (as opposed to 0) and I suspect MAME has it right but we'll see. Cheers Chr...
by scarybeasts
Mon Dec 31, 2018 9:11 am
Forum: emulators
Topic: 6522 VIA emulation: IFR write vs. timer interrupt
Replies: 8
Views: 353

Re: 6522 VIA emulation: IFR write vs. timer interrupt

From a Beeb: (Edit, ran it 10 times and always got 1,192) Thanks! Super interesting. Finally the mighty jsbeeb is defeated in a core VIA timing issue. This result does kind of have a symmetry with Rich's results though: it seems any time there's a VIA cycle where the timer is firing at the same tim...
by scarybeasts
Mon Dec 31, 2018 8:02 am
Forum: emulators
Topic: 6522 VIA emulation: IFR write vs. timer interrupt
Replies: 8
Views: 353

6522 VIA emulation: IFR write vs. timer interrupt

Hi, Test case: VIA.I2 in the attached SSD. This test case clears the timer interrupt in the IFR register on the same VIA cycle that fires the timer interrupt. As usual, the emulators disagree. jsbeeb and beebem (an unusual combination of agreement) think that the timer interrupt is canceled. The res...
by scarybeasts
Mon Dec 31, 2018 3:47 am
Forum: emulators
Topic: 6522 VIA emulation: ACR writes
Replies: 19
Views: 650

Re: 6522 VIA emulation: ACR writes

I noticed that MAME and b2 both have code that re-arms the T1 interrupt if ACR is written and continuous mode selected. In b2's case, I assume this will be this recent change , which I added to sort out some horrid-looking scrolling in Planetoid, after being inspired by your T1/PB7 thread to look a...
by scarybeasts
Mon Dec 31, 2018 3:30 am
Forum: emulators
Topic: 6522 VIA emulation: ACR writes
Replies: 19
Views: 650

Re: 6522 VIA emulation: ACR writes

Is it the case, for example, that the IFR timer bits update immediately a timer expires rather than waiting for the next clock, whereas the IFR bit 7 and external /IRQ line take an additional clock cycle to update? Does anyone know the answer to that or it is easier to run a test case? I think the ...
by scarybeasts
Mon Dec 31, 2018 3:05 am
Forum: emulators
Topic: 6522 VIA emulation: T1LH writes vs. T1 interrupt
Replies: 11
Views: 596

Re: 6522 VIA emulation: T1LH writes vs. T1 interrupt

Hmm, but that if statement must have been put in for some reason? Heh, reason lost in the mists of time? jsbeeb's VIA logic is based on b-em's best I know. Why does b-em have that logic? No idea but looking at some of the even older emulators: BeebInC (1998?) has a commented out version of this if ...
by scarybeasts
Sun Dec 30, 2018 7:15 am
Forum: emulators
Topic: 6522 VIA emulation: ACR writes
Replies: 19
Views: 650

Re: 6522 VIA emulation: ACR writes

Thanks again BigEd / Coeus! And some instructive / interesting results. In terms of what I was trying to test: this seems to show that writing ACR doesn't have any special behavior such as re-arming timers. This again is the simpler result and suggests a simplification fix can be applied to b2 / MAM...
by scarybeasts
Sun Dec 30, 2018 6:18 am
Forum: emulators
Topic: 6522 VIA emulation: T1LH writes vs. T1 interrupt
Replies: 11
Views: 596

Re: 6522 VIA emulation: T1LH writes vs. T1 interrupt

Thanks BigEd!

Nice simple resolution, and both jsbeeb and b-em get to remove an if statement which is strangely satisfying :-)


Cheers
Chris