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Hello community!

Hello everyone. C=64 guy here.

I was looking for ways to integrate digital joystick to PC for using with VICE. While copying PPjoy URLs to my C64 folder on PC, I found and old link pointing to retrogamecoders. And here has a community forum. So why not join...

A quick question, I can ask it seperately though.

For C=64 BASIC V2 and DOS 2.6 on VICE. I have a simple BASIC code to read error info of diskette device. Open a handle (15) to command channel (15) of device (8-11). Read 4 parameters (INPUT#15), display them. If the device, (8-11) in question is attached and powered up, works like a charm. But when the device is not attached and not powered up (in means of the emulator: None), BASIC hangs, not responding to anything but reset. It is obvious that's because "read from device" (INPUT#) instruction but I couldn't understand why it just does not throw "DEVICE NOT PRESENT" just like when using "write to -a not attached- device" (PRINT#) ?
So, is there a non-destructive command (that won't alter current error status) to send either check if the device is attached, or let BASIC to throw "DEVICE NOT PRESENT" error?

Hello community!
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  • 3 comments

Matt Armstrong

Sorry can't help you there. I was on the other side of the fence, I owned a ZX Spectrum..

C64Whiz

So I tested this under Vice 3.3. I setup a drive 8 and 9, and testing both came back with valid data. When I attempted device 10, it "hung", but I was able to RUN/STOP-RESTORE to get the cursor back...I didn't have to reset the emulator. I performed this test on a Ultimate 64 as well with same results...valid output for connected drives, RUN/STOP-RESTORE to get back from "hung" on non-existent drives.

However, the "hanging" should be preventable by investigating the ST variable after opening the channel. In the "Complete Guide to the 1541 Disk Drive" (https://archive.org/details/1541_Users_Guide_1984_Datamost), page 232-233, it shows a 6510 assembly language checking the ST variable after attempting to open the channel in order to see if the device is not present (ST=-128). However, when I modify the BASICv2 program:

35 IF ST <>0 THEN PRINT "NOPE":END

it still "hangs" with ST=0. (Same results on the Ultimate.) I'm not sure why...

However, there IS a work-around: CLOSE the channel immediately after opening it:

OPEN15,8,15
CLOSE 15
IF ST = -128 THEN PRINT "DEVICE NOT PRESENT":END

This worked for me both in VICE and on the Ultimate 64. Just remember you'll need to re-open prior to your INPUT#.

HTH

--C64Whiz

P.S. Here is a link to a demo program in the RGC emulator. (I'm new here too...had to check this out! 😆 )

Chris Garrett

C64Whiz Nice! I am working on a .D64 editor for the IDE too :) I found some python modules that seem to work so it will be a wrapper around those, failing that I will use the vice tools on the server