Hi! While debugging the VICE CBM-II emulation (C610-C720) I found something interesting. Using the CBM-II emulation with a 2031 disk drive seems to result - at least in VICE - in a randomly occuring file not found error with ST=3: During a load operation (FFD5), after sending the IEC UNLISTEN (after sending the filename) the CBM-II immediately proceeds to send the IEC TALK to start the data transfer. However, as the CBM-II runs a 2MHZ, the CBM-II is much faster than the disk drive. So when the drive detects the ATN low from the CBM-II it resets the bus, which includes setting atna up to block the bus on ATN by setting nrfd & ndac lo. The CBM-II on the other side waits for NRFD hi to start the send. resetting the bus from the drive (STA $1800 @ E953) now happens basically the same time the cpu first checks for nrfd hi (LDA $DE00 @ F2D4), and in VICE this can now happen in both orders. When the drive is first it works, when the CBM-II is first is gives a file not found error. This error does not seem to happen in a 4040 drive for example. Now I have two questions: - Has anyone experienced this problem with a real C610/620/710/720, B128/B256 and a real 2031? - Does the 2031 really run at 1MHz, and the CBM really on 2MHz? - I analysed this from a combined VICE trace log from the drive and the main CPU. But somehow I can't believe that this is the full truth, for me it is just too close. I know noone has much time, but can someone please verify this behaviour by code review? Many thanks! Andre - This message was sent through the cbm-hackers mailing list. To unsubscribe: echo unsubscribe | mail firstname.lastname@example.org.
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