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MiSTer-devel / C128_MiSTer

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In C128 mode disk images mounted in the internal drive can't be accessed when "external iec" is enabled #36

Closed thierer closed 6 months ago

thierer commented 7 months ago

When in C128 mode and the "External IEC" option is enabled (but no external drive is attached), disk images mounted in an internal drive (using Mount #8 or Mount #9) can't be accessed (LOAD "$",8 hangs at SEARCHING FOR $).

This works fine in C64_Mister and even in the C64 mode of this core.

I noticed this in the 20240110 release, but I tested a few older releases and it seems it never worked.

eriks5 commented 6 months ago

I can't reproduce this, it works fine for me.

I suspect it's because of a difference between the IEC adapter we're using. Does the one you use support the fast serial protocol with the 1571/1581 drives? What happens if you configure the drive as a 1541?

If the USERIO6/SRQ line, which is used only for fast serial, is floating or pulled to GND this would happen. The IEC bus is a "party" bus. Lines are pulled high using resistors in the external drives and any device that wishes to talk on it pulls the line to GND. If no drive is connected, there are no pull-up resistors and when the SRQ line remains low, this affects the internal drives as they cannot control the SRQ line.

thierer commented 6 months ago

You're absolutely right, the SRQ line is to blame. If I force a 1541 it works. My IEC adapter might very well be to blame, though I don't understand why it would only affect SRQ (and all lines including SRQ do have pullups). But something's strange, so I'll close this at least until I better understand what's going on. Sorry for the noise!