Virtualc64: Rom-Ram Test Cartridge

[Alessandro1970]

Hi, I have found this cartridge test:
romram.crt.zip

Vice:

VirtualC64:

...maybe it is only an unsupported cartridge !

[dirkwhoffmann]

🤔 Seems like this cartridge is performing a test and VirtualC64 fails on that test.

I expect this to be a bug in the emulator. Needs investigation...

[rossimariolee]

Hello, a blue screen for me too.
Is this really a bug ?

[Alessandro1970]

Yes it is, this romram.crt is a test that I have found also here:

https://vice-emu.pokefinder.org/index.php/Testbench

I have seen that it works on VICESC and in HOXS64

[sarnau]

This cartridge actually just tests if EasyFlash is emulated correctly. The code is actually quite trivial:

; +-------------------------------------------------------------------------+
; |      This file was generated by The Interactive Disassembler (IDA)      |
; |           Copyright (c) 2020 Hex-Rays, <[email protected]>           |
; |                      License info: 48-3051-7314-20                      |
; |                       Markus Fritze, personal use                       |
; +-------------------------------------------------------------------------+

                .org 8000h
loc_8000:   SEI
                LDA     #7
                STA     0DE02h      ; EasyFlash: 16 Kb cart  (low bank at $8000, high bank at $a000)

; Copy 512 bytes to RAM
                LDX     #0
loc_8008:       LDA     loc_8000,X
                STA     loc_8000,X
                LDA     byte_8100,X
                STA     byte_8100,X
                INX
                BNE     loc_8008

                LDA     #4Ch        ; patch a JMP opcode into RAM
                STA     loc_8021
                LDA     #4
                STA     0DE02h      ; EasyFlash: Cartridge ROM off (256 Bytes of RAM still available at $dfxx)

loc_8021:       LDA     loc_8031    ; This should now be a JMP, if the ROM is off

                LDA     #2      ; red = fail
                STA     0D020h      ; VIA border color
                LDA     #0FFh
                STA     0D7FFh      ; exit emulator with code 255 (fail) - used by Kernal64
endless_a:      JMP     endless_a


loc_8031:       LDA     #5      ; green = success
                STA     0D020h      ; VIA border color
                LDA     #0
                STA     0D7FFh      ; exit emulator with code 0 (success) - used by Kernal64
endless_b:      JMP     endless_b

The details for EasyFlash can be found here

[sarnau]

Without the green or red border, the crt is probably not recognized correctly.

[dirkwhoffmann]

Might be related to #564. I'll look into it...

[dirkwhoffmann]

My EasyFlash implementation doesn't handle the write correctly:

LDA     #4Ch        ; patch a JMP opcode into RAM
STA     loc_8021

If a ROM location is written to, it passes the write request to the Flash Roms, but doesn't write the value into the C64 RAM. Hence, it reads back a BRK where the JMP should be 🙄.

Working on a fix...

[dirkwhoffmann]

Green border 😎:

However, it looks different than the first screenshot in this thread. In the sources, I can't see anything that would change the canvas background color. Was it perhaps a different test cartridge?

[sarnau]

Maybe, I looked at the code in the cartridge, which was attached. There is clearly no background color access.

[sarnau]

Maybe VICE acts on the write to 0D7FFh and exits the emulation, resulting in a weird green background?

[dirkwhoffmann]

Maybe VICE acts on the write to 0D7FFh and exits the emulation, resulting in a weird green background?

STA     0D7FFh      ; exit emulator with code 0 (success) - used by Kernal64

Oh yes, I haven't seen this. VirtualC64 continues to run normally and I guess this makes the difference.

I've checked in the fix on the dev branch where v4.0 is being developed. If nobody complains, I'll ignore the v3.4 branch.

[dirkwhoffmann]

Maybe VICE acts on the write to 0D7FFh and exits the emulation, resulting in a weird green background?

It's the "Debugcart" feature which is enable by passing "-debugcart" to VICE as a command line parameter:

https://vice-emu.pokefinder.org/index.php/Debugcart

Starting with v4.0, VirtualC64 will support "-debugcart", too.

[sarnau]

You are on fire 👍