#337 tape hooks to check CARRY flag

[ub880d]

tape hooks don't check CARRY flag to be set for LOAD and cleared for VERIFY. result is when VERIFY is requested, LOAD is performed instead.

test tap http://sindik.at/~ub880d/tmp/loadtest.tap , code is:

    cpu z80undoc
    relaxed on

    org 32768
    xor a
    ld  ix,0x4000
    ld  de,0x1b00
    ld  a,255
;    scf                ;scf for load, no carry for verify
    call    0x556
    ret

this program shouldn't load headless screen (included in the tap). but fuse with enabled tape traps loads it.

[Fredrick Meunier]

Thanks, applied in [r5311].

[Fredrick Meunier]

On fuse-emulator-devel, Alberto Garcia reports a problem with this patch:

On Wed, Jun 01, 2016 at 03:33:16PM +0200, Alberto Garcia wrote:

I cannot load LoneWolf-TheMirrorOfDeath128.tap.zip using the new
Fuse (the loading screen does not even show up). With Fuse 1.1.1 it
works fine.

http://www.worldofspectrum.org/infoseekid.cgi?id=0002920

Here's the cause of this problem:

20150704 tape.c: skip tape traps if VERIFY is requested (patch #337) (UB880D).

The TZX version is also problematic, but Fuse 1.1.1 was having
issues with that one too.

Actually it seems that I cannot load this one at all, not even with
--no-detect-loader --no-auto-load --no-traps --no-fastload
--no-accelerate-loader

Interestingly enough, if I convert the .tzx to a .tap file (with all
the "conversion may well not work" warnings) then I can load it just
fine (with both 1.1.1 and 1.2).

[Fredrick Meunier]

Thanks to Berto's report, I've had another look at this change and I believe we are being caught by a longstanding bug introduced in 2004 with [patches:#41] Fix up registers on tape load trap in [r2137].

trap_load_block() was already intended to cover the verify case so [patches:#337] should not have been required, but [patches:#41] added the line

AF_ = 0x0145;

which hardcodes the value of the verify flag (the C flag in the F' register) before it is later tested for verify behaviour.

The attached patch fix_verify_with_tape_traps.patch removes tape_traps_verify.diff and restores the older verify detection code.

This keeps loadtest.tap working with the verify being done by the tape trap but isn't enough alone to sort out what's going on with Lone Wolf 3.

The Lone Wolf 3 tap looks broken to me - it seems to set the verify flag for several of the blocks which won't load under any situation. My guess is that this tap has been preparared and only tested by using it with systems that shortcut loading for tap blocks like emulator traps or ESXDOS TAP loading etc.

The Lone Wolf 3 tzx on the other hand seems to have problematic encoding. Doing some experiments changing its encoding to pzx I can get it to load (only tested without accelleration), but I will need to do some more tests to work out what exactly is the difference between the broken tzx and working pzx versions I have in order to decide whether that is resolvable with a Fuse patch. My gut feel is that this will boil down to a problem with the tzx encoding of Lone Wolf 3 rather than Fuse.

[ub880d]

Answer for tap file is here:

0xFDB4 DD 21 1C FB  LD      IX,0xFB1C
0xFDB8 21 15 00     LD      HL,0x0015
0xFDBB 3E 36        LD      A,0x36
0xFDBD 37           SCF     
0xFDBE CD C4 FC     CALL    0xFCC4

===

0xFE07 DD 2A 5B FB  LD      IX,(0xFB5B)
0xFE0B 2A 2D FB     LD      HL,(0xFB2D)
0xFE0E 3E 69        LD      A,0x69
0xFE10 B7           OR      A
0xFE11 CD C4 FC     CALL    0xFCC4

===

0xFCC4 ED 73 05 FB  LD      (0xFB05),SP
0xFCC8 E5           PUSH    HL
0xFCC9 F5           PUSH    AF
0xFCCA 01 19 00     LD      BC,0x0019
0xFCCD CD 11 FF     CALL    0xFF11
0xFCD0 CD 07 FD     CALL    0xFD07
0xFCD3 D9           EXX     
0xFCD4 21 FF FF     LD      HL,0xFFFF
0xFCD7 F1           POP     AF
0xFCD8 E1           POP     HL
0xFCD9 C3 FF FC     JP      0xFCFF

===

0xFF11 32 59 FB     LD      (0xFB59),A
0xFF14 F3           DI      
0xFF15 C9           RET     

===

0xFD07 54           LD      D,H
0xFD08 5D           LD      E,L
0xFD09 CD 56 05     CALL    0x0556
0xFD0C F3           DI      
0xFD0D ED 7B 05 FB  LD      SP,(0xFB05)
0xFD11 C9           RET     

first "call 0xfcc4" is to load header, second to load data of block, but there is "or a" at 0xFE10, so carry is reset. changing the instruction to "scf" game loads correctly.

[Alberto Garcia]

The Lone Wolf 3 tap looks broken to me - it seems to set the verify flag for several of the blocks which won't load under any situation.

How come it is working with Fuse 1.1.1 then ? :-? I'm still unable to load it with the latest trunk.

[ub880d]

Alberto, it is not a bug that you cannot load the tape. The bug is if you can load the tap.

I already posted my analysis of the loader code in the tap.

If you disable the tape traps in emulator it is not possible to load the tape even in 1.1.1 (which is correct behavior).

[Alberto Garcia]

Ah sorry, you're right!

[Fredrick Meunier]

Comitted fix_verify_with_tape_traps.patch in [r5586] and [r5587].

[Fredrick Meunier]

Following up on the tzx issues in [bugs:#352] Problems loading Lone Wolf 3 - The Mirror of Death.tzx as they seem to be separate.