Error in Apple 2 rom about apple2js HOT 3 CLOSED

Very interesting. I noticed a couple of things:

• The program is not exactly correct. On the first line #FE should be #BE if you want a > as a prompt.
• The program does print out HELLO ALL, but then runs ALL as if it were typed in to the monitor (as you say).
• As expected, HELLO E003G will return to BASIC.
• 1000G is exactly the same length as HELLO.

If you look at the Apple //e monitor ROM listings, the monitor entry code is at FF69. One of the first things it does is JSR GETLNZ, which is the same as the program above. It then decodes the command (and all hex numbers before it) and then executes it at FF82 with JSR TOSUB. TOSUB then executes the command through the jump table at FFE3 by pushing and address on the stack and then doing an RTS. The G command is implemented at FEB6. The jump to the user address happens at FEBC as an indirect jump through 003A. But note that this is a JMP not a JSR. This means that when the program's RTS happens, it's actually returning from the JSR TOSUB. As commented at FF85, this proceeds to process the next entry on the line—but that has been overwritten by the program. This is why anything after HELLO is interpreted by the monitor.

Thus, I don't think there's actually anything wrong with the ROM here.

Hope that helps!

from apple2js.

I confirm the same happens with an Apple ][+ ROM from https://ftp.apple.asimov.net loaded into another emulator. That confirms there's nothing wrong with the ROM in Apple2js, and I think this issue could be closed.

from apple2js.

Glad to hear it.

from apple2js.