- BBC F0 is F10
- BBC Break key is F12
- BBC star is on " (if it doesn't work for you try shift-2)
To play right now, visit http://bbc.godbolt.org/. To load the default disc image (Elite in this case), press shift-F12 (which is shift-Break on the BBC).
Getting set up to run locally
Fire up a local webserver and load it up. I use
python for this as it has a built-in webserver. So:
$ cd jsbeeb $ python -mSimpleHTTPServer Serving HTTP on 0.0.0.0 port 8000 ...
Then visit http://localhost:8000/ and off you go.
autoboot- fakes a shift break
disc1=XXX- loads disc XXX (from the
discs/directory) into drive 1
disc2=XXX- as above
disc1=local:YYY- creates a local disk YYY which will be kept in browser local storage
disc1=sth:ZZZ- loads disc ZZZ from the Stairway to Hell archive
tape=XXX- loads tape XXX (from the
tape=sth:ZZZ- loads tape ZZZ from the Stairway to Hell archive
patch=P- applies a memory patch
P. See below.
loadBasic=X- loads 'X' (a resource on the webserver) as text, tokenises it and puts it in
PAGEas if you'd typed it in to the emulator
*/to run from tape. In conjunction with
CH.""to run from tape.a
embed- Adjust the navigation entries to make the page clearer within a 921x733 iframe in a third-party site.
cpuMultiplier=Xspeeds up the CPU by a factor of
X. May be fractional or below one to slow the CPU down. NB disc loads become unreliable with a too-slow CPU, and running too fast might cause the browser to hang.
sbBottom- a URL to place left of, right of, or below the cub monitor. The left and right should be around 648 high and the bottom image should be around 896 wide. Left and right wider than 300 will run into problems on smaller screens; bottom taller than 100 or so similarly.
videoCyclesBatch- the number of video cycles to batch up befofre running the video emulation. Defaults to zero: anything higher leads to emulation inaccuracies. Useful for showing why accuracy is important, even if less efficient.
rom- load the given URL or path as an extra ROM. If a URL is provided, that URL must allow cross-site requests. Doesn't (yet) support the sth: pseudo URL unlike
Patches can be applied by making a
patch=P URL parameter.
P is a sequence of semicolon separated patches of the form
@XXXX,YYYY:ZZZZZ,... where the
@XXXX specifies a PC address to breakpoint, the
YYYY is the address to patch and the
ZZZZ is the data to write at address
@ part is optional, but is handy to ensure the code you want to patch has actually loaded. For example:
patch=@31a6,0769:6e4c4d48465a which is a patch for the default Elite image. Once the PC has reached
$31a6, the bytes at
0769 are replaced with
Things left to do
If you're looking to help:
- Save state ability
- Once we have this I'd love to get some "reverse step" debugging support
- Save state ability
- Save disc support
- Local discs need to be made more workable and need an "export" feature
- Multiple discs need a UI
git grep -i todo
- While every attempt to make things fast has been made, I'm sure there's some more clever things that can be done without compromising emulation accuracy
For general correctness there are several tests in the
tests directory, including:
- Klaus Dormann's exhaustive test of all documented opcodes for 6502 and 65C12. This is brought in as a git submodule from a forked version of Klaus's original as it needed a few tweaks to get 65C12 working.
- hoglet's Binary Coded Decimal tests.
- A public domain Commodore 64 6502 test suite which tests every 6502 opcode (documented or otherwise) for every possible input and flags condition.
For timing correctness we have:
- A timing test program written by Rich. It has been run on a real live BBC B and
the results are in the directory. An SSD of the same tests is in the
- Some of Kevin Edwards' protection systems (stripped of the games themselves). These are extremely timing- and correctness-sensitive when it comes to the timers and interrupts of the BBC.
- Some 65C12-specific read-modify-write tests written by Ed Spittles.
Tests can be run automatically if you have
node installed - just run
make and it'll ensure the relevant libraries are installed, then it'll run the tests.
Please note it can take a while to run the whole test suite.
jsbeeb was heavily based on Sarah Walker's C B-Em emulator -- thanks to her for her hard work and for open sourcing her code.
Huge thanks to Richard Talbot-Watkins for his advice and help along the way in fathoming out the instruction timings, interrupt fun, video code rewrite and for being such a good pal all these many years!
Thanks to David Banks (hoglet) for his help in testing the gnarly BCD flag behaviour on real live BBCs.
Cheers to Ed Spittles for testing various interrupt timing code on a real BBC.
Thanks to Chris Jordan for his thorough testing, bug reports, ideas and help.
A lot of the early development used the amazing Visual 6502 as reference for intra-instruction timings. Amazing stuff.
Special shout out the users of the 6502 Forums
I've written a lot of how the innards work on my blog in the emulation section.
I gave a presentation on how it all fits together at work, and posted the video up on YouTube. I presented again at GOTO Chicago 2016, and I'm hoping they post the video up.