I have a vague recollection there's already something in the ROM for a double break...
Yep, quite right - just tried this out in b2. CTRL+BREAK is an ordinary break and a quick double tap of BREAK is a hard break. I'll have a look at Toby's disassembly to see how exactly it's doing this.There was in OS 0.1 I think - that was the old "hard break" mechanism.
Ha... good spot! One for the MOS bugs thread, I think. The memory is cleared from $0000 upwards, doing all of $0000...$dfff in one go with the utils ROM selected (so the writes to $8000...$bfff do nothing): https://github.com/tom-seddon/acorn_mos ... t.s65#L145 - and of course, this means it resets the escape/break effect flag early on.Double break already unwittingly does something on the Master. If "clear on reset" *FX 200 is on, a second Break interrupts the RAM clear and leaves it untouched. I used to do this all the time back in the day as a loophole for getting through protection systems. You've got to be quick!
I might actually fix this, just to be annoying. Clearing backwards should do the trick...
--Tom
P.S. OS 1.20 bypasses this by clearing from $0400 onwards: https://tobylobster.github.io/mos/mos/S-s10.html#SP4
Statistics: Posted by tom_seddon — Tue Feb 25, 2025 9:41 pm