English Amiga Board - View Single Post - CIA-A DDRA fixed I/O bits direction

ross · 11 November 2018, 15:49

Another thread where I was undecided whether to write in support.WinUAE or in the Coders.Asm/Hardware section.

This time this section won

I'm debugging an old game, that only work in KS1.x and only in some configurations, in an attempt to patch it (a not so simple job).
A game from 1987/88 that mix system code and hardware banging.
It use system to open multiple screens then mess with copper list to switch between them..
If you drag the main screen, after a while, game crash.

Original programmer, in an attempt to prevent this, used a strange method:

Code:

	move.b	#$43,($BFE201)

So DDRA(/FIR0) as an output.

WinUAE take /FIR0 as usual and screen dragging is permitted (and crash).
How a real machine behave?
Is the left mouse button really inhibited in this way or is it the programmer who's completely wrong?

Thanks.

11 November 2018, 15:49	#1
ross Defendit numerus Join Date: Mar 2017 Location: Crossing the Rubicon Age: 53 Posts: 4,475	CIA-A DDRA fixed I/O bits direction Another thread where I was undecided whether to write in support.WinUAE or in the Coders.Asm/Hardware section. This time this section won I'm debugging an old game, that only work in KS1.x and only in some configurations, in an attempt to patch it (a not so simple job). A game from 1987/88 that mix system code and hardware banging. It use system to open multiple screens then mess with copper list to switch between them.. If you drag the main screen, after a while, game crash. Original programmer, in an attempt to prevent this, used a strange method: Code: move.b #$43,($BFE201) So DDRA(/FIR0) as an output. WinUAE take /FIR0 as usual and screen dragging is permitted (and crash). How a real machine behave? Is the left mouse button really inhibited in this way or is it the programmer who's completely wrong? Thanks.