On Wed, Mar 08, 2017 at 06:45:01PM +0100, email@example.com wrote: > i am investigating differences in the CIA behaviours (NMOS vs HMOS versions, > ie 6526 vs 8521) at the moment. one thing that is pretty unclear to me, is a > supposed bug in the TOD alarm behaviour. i can find some references to it on > the web, which somehow look like one copied from the other to me - without > ever mentioning the exact details: There also is 8520. I haven't yet seen good pictures of the 8521, but the pictures that are there show that 8520 and 8521 are nothing alike (and neither is like the 6526, either -- in the physical layout anyway). > wikipedia: > "Due to a bug in many 6526s the alarm IRQ would not always occur when the > seconds component of the alarm time is exactly zero. The workaround is to set > the alarm's tenths value to 0.1 seconds." > > http://forum.6502.org/viewtopic.php?p=9837#p9837 > "There was also a problem with the Time of Day clock alarm interrupt, which > would not occur if the alarm time tenths-of-seconds was set to zero. The > solution was to set the tenths to anything other than zero." > > ... "we" have created a bunch of test programs  in the past already, and > they indeed show some odd behaviour under certain conditions (including the > alarm not triggering when it should) - but so far these tests behave exactly > the same on "old" and "new" CIAs. > > so i am asking you guys a) if you have heard about the above mentioned > problem, and can tell details on the condition needed to reproduce it (so i > can make it test program - or perhaps even you can provide one) and b) if this > is really a problem that should only show on one of the two CIA variants > (probably the older one). also if you know and references/documents that > mention this problem, please tell! I'll have a look at the die pics again, this weekend I hope. Segher Message was sent through the cbm-hackers mailing listReceived on 2017-03-09 23:00:02
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