(71B) FORTH questions

[David Hayden]

(06-16-2023 05:39 PM)Giuseppe Donnini Wrote:  I can, therefore, confirm that the bug was indeed fixed in ROM revision 2CDCC. Here is my own disassembly of GETTIM for both the 1BBBB and the 2CDCC revisions.
...
2CDCC

Code:


1254A 04         GETTIM SETHEX
1254C 1B8F2E2           D0=(5)  =TIMER2        Point to timer in disp driv.
12553 AF0               A=0     W
12556 15A5              A=DAT0  6              Read timer
1255A 25                P=      5              [GD: Set value of P *before* using...]
1255C A98               B=A     WP             [    ...WP for the first time!]
1255F 15A5              A=DAT0  6              Read again.
12563 910               ?A=B    WP             Kerchunk anywhere?
12566 60                GOYES   GETTM2         No.  Reads are good.
12568 15A5              A=DAT0  6              Yes.  One more read.
1256C A88        GETTM2 B=A     P
1256F A05               B=B+B   P              Negative?
12572 500               RTNNC                  No
12575 B98               A=-A    WP             Yes.  perform sign-extend
12578 BF8               A=-A    W
1257B 02                RTNSC

I'm late to the party, so I may just misunderstand the issue, but even this fixed code looks wrong to me because it assumes that when value1 != value2, value 2 is the correct one. Shouldn't it basically loop until it reads two consecutive values that are the same?