#1974 A monitor error in x128 Bank1 c64mode

[Jussi Ala-Könni]

In x128, when b1c64mode.prg is executed, the mode setup code is copied to bank 1 $3800-. When Monitor is activated, it sees the byte $3800 as $2f, yet in memory it is really $a9 = 169 (LDA #). The copied code is otherwise listed correctly.

[Jussi Ala-Könni]

It worked in r43499 and r43787, but r44109 has the error. In the in-between r44070 b1c64mode.prg did not work.

[Olaf Seibert]

Yes, I can reproduce it if I run x128 -default b1c64mode.prg, then go into the monitor:

Available banks (some may be equivalent to others):
*default    *cpu    ram     rom     io  ram00-01    intfunc     extfunc     cart    c64rom  vdc     
(C:$e5d1) d 3800 3800 
.C:3800  2F 40 8D    RLA $8D40
(C:$3803) bank ram01
(C:$3803) d 3800 3800 
.C:3800  A9 40       LDA #$40
(C:$3802) 

[Olaf Seibert]

I was the last one to touch the monitor code that reads the memory for the D and M commands, but I think I traced this to something else.

To trace what the monitor is reading, I set a breakpoint at c128mem.c:mem_bank_peek()
-> case bank256_cpu:
-> mem_peek_with_config(mem_config which is 7
-> no special case applies, so at the bottom
-> mem_peek_with_config_c64(config
-> ram_peek_c64(addr)

        uint8_t *b = mem_read_base_tab[mem_config][addr >> 8];
        if ((addr & 0xff) == 0) {
            return zero_peek(addr);
        } else if ((addr & 0xff) == 1) {
            return one_peek(addr);
        }
        return b[addr];

I didn't write the 128 banking code (I just know it was much more complicated than previously thought) but I strongly suspect that these comparisons should be

        if ((addr & 0xff00) == 0x0000) {
        if ((addr & 0xff00) == 0x0100) {

@oldwoman37, do you agree?

Oh, and in the call from mem_peek_with_config_c64(config to ram_peek_c64(), the config parameter is lost and instead the global mem_config is used. That is incorrect, but will probably always work anyway since the only value for config that the monitor will ever use will be the current_config.

[Roberto Muscedere]

Yes, this seems like it would be a problem. Please go ahead and commit the change. My current changes would break everything else.

[Jussi Ala-Könni]

When the CPU I/O port $00 value is changed from $2f, then the address $3800 value in the monitor changes accordingly. Here the change is from $2f > $af = 175.

The error occurs in normal C64 mode as well.

[Olaf Seibert]

I committed the proposed fix in r44940. Please retest when the build is available from https://github.com/VICE-Team/svn-mirror/releases . Thanks!

[Querino]

i tested it before, and it solved the issue for me. but i am no experienced user.

[Jussi Ala-Könni]

After a quick test I see no problems.

[Olaf Seibert]

Great! I'll close this one then.