Hallo Gerrit, > Which ROM version did you look at? There were 2 for the 1581, > 318045-01 and 318045-02. This part is the same for both versions. The main thing V2 does is adding a SEI somewhere. And the guy who did it it was very lazy: he disabled the checksum routine to save him the work of calculating a new check sum. > so are you sure the WD177x is ever in the state necessary > to hit this bug? I'm not. But if the WD177x never comes in this state, then why is it being checked at all? I just checked the datasheet and IMHO the checked byte means that "the computer did not respond to DRQ within one byte time". As the 1581 doesn't use DRQ at all, this error could never occur. But then there also wouldn't any need to check it at all in the first place! Just a very, very, wild guess: the code was written before the final design and stayed because nobody noticed or cared. PHP and PLP were added later by someone who didn't understand the code or indeed made an error. And being a piece of dead code now, it couldn't do any harm and therefore it went unnoticed. And to quote SilverDream again: > the guys had simply too much room in the 1581 ROM chip to care > about couple bytes here or there. It doesn't do any harm but doesn't make sense as well: > lda #9 > sta ContrStat > > lda ContrStat Why the last "LDA"? -- ___ / __|__ / / |_/ Groetjes, Ruud Baltissen \ \__|_\ \___| http://Ruud.C64.org Message was sent through the cbm-hackers mailing listReceived on 2012-02-08 17:00:39
Archive generated by hypermail 2.2.0.