Porting Yquest 6502 to the BBC

The BBC version was the first port of the game on the 6502.
The BBC is a bitmap based system, with software sprites. Lets take a look at the code.

As always, this Video lesson matches the text lesson on my website, and you
can get the source code as well...

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[trickysoft]

I'm amazed that you are converting so many machines. Well done.
I notice that your sound code doesn't leave the required time between turning on the connection to the sound chip and turning it off again. This will work fine on some emulators, but will be unpredictable on others and hardware. Adding pha:pla:nop:nop should be just enough.
Also why 160 horizontally when both the cpc and beeb are 320 in mode 1?
Great work, keep 'em coming.

[trickysoft]

Second fire buttons is the but next to the first ;) just typing as you go. Some emulators don't sort the second fire button.

[trickysoft]

PS, another reason that it might be slower than you expect is your spending 8ms out of 20ms waiting for the ADC to complete ;) - still loving this series and am planning on going through your 6809 one at some point.

[trickysoft]

Lots of early 8 bit games and some later ones moved the player in pixels, but everything else in characters.
Have you considered adding a vsync wait routine, on the Beeb it is quite easy, even without interrupt handling and no OS.