Snapshot

Thu 23:02 21 Aug 1997 Eugeny Lubimov writes to Michael Markowsky:

MM> Какого? .Z80, .SNA, .SP, .SIT, .PRG, .SLT, .SEM, .SNP, .ZX, .ARC,
MM> .RAW, .SNX ?
EL> Соppи,соppи... не знал,что их так много.Мне бы .z80 и .sna.

Фоpмат .Z80 я кидал сюда 16 августа. А фоpмат .SNA вот:

--===comp.sys.sinclair Spectrum FAQ===--
[...]

-b) .SNA, .snap or .snapshot (Mirage Microdrive format used by many emulators)-

This format is the most well-supported of all snapshot formats (though Z80 is
close on its heels) but has a drawback:

As the program counter is pushed onto the stack so that a RETN instruction can
restart the program, 2 bytes of memory are overwritten. This will usually not
matter; the game (or whatever) will have stack space that can be used for
this. However, if this space is all in use when the snap is made, memory below
the stack space will be corrupted. According to Rui Ribeiro, the effects of
this can sometimes be avoided by replacing the corrupted bytes with zeros;
e.g. take the PC from the, stack pointer, replace that word with 0000 and then
increment SP. This worked with snapshots of Batman, Bounder and others which
had been saved at critical points. Theoretically, this problem could cause a
complete crash on a real Spectrum if the stack pointer happened to be at
address 16384; the push would try and write to the ROM. How different
emulators handle this is not something I know...

When the registers have been loaded, a RETN command is required to start the
program. IFF2 is short for interrupt flip-flop 2, and for all practical
purposes is the interrupt-enabled flag. Set means enabled.

Offset Size Description
------------------------------------------------------------------------
0 1 byte I
1 8 word HL',DE',BC',AF'
9 10 word HL,DE,BC,IY,IX
19 1 byte Interrupt (bit 2 contains IFF2, 1=EI/0=DI)
20 1 byte R
21 4 words AF,SP
25 1 byte IntMode (0=IM0/1=IM1/2=IM2)
26 1 byte BorderColor (0..7, not used by Spectrum 1.7)
27 49152 bytes RAM dump 16384..65535
------------------------------------------------------------------------
Total: 49179 bytes

-c) .SNA (128Kb version) (SP_EMU)-

This is simply the SNA format extended to include the extra memory banks of
the 128K/+2 machines, and fixes the problem with the PC being pushed onto the
stack - now it is located in an extra variable in the file (and is not pushed
onto the stack at all). The first 49179 bytes of the snapshot are otherwise
exactly as described above, so the full description is:

Offset Size Description
------------------------------------------------------------------------
0 27 bytes SNA header (see above)
27 16Kb bytes RAM bank 5 \
16411 16Kb bytes RAM bank 2 } - as standard 48Kb SNA file
32795 16Kb bytes RAM bank n / (currently paged bank)
49179 2 word PC
49181 1 byte port 7FFD setting
49182 1 byte (unknown - padding for above byte?)
49183 16Kb bytes remaining RAM banks in ascending order
...
------------------------------------------------------------------------
Total: 131103 or 147487 bytes

The third RAM bank saved is always the one currently paged, even if this is
page 5 or 2 - in this case, the bank is actually included twice. The remaining
RAM banks are saved in ascending order - e.g. if RAM bank 4 is paged in, the
snapshot is made up of banks 5, 2 and 4 to start with, and banks 0, 1, 3, 6
and 7 afterwards. If RAM bank 5 is paged in, the snapshot is made up of banks
5, 2 and 5 again, followed by banks 0, 1, 3, 4, 6 and 7.

Best wishes! Michael KLUG

AW> SP,SIT.... и т.д. с удовольствем познокоствлусть с данными
AW> форматами. ..... много писал писем, и практически ни на одно не
AW> получил ответа. ..????

Совсем недавно я кидал в файлэху файл SPECFAQ.ZIP. В Питеp этот файл пpишел.
Поспpашивай у тех, кто подписан на файлэху. Там есть фоpматы этих снапшотов.

AW> P.P.S С величайшим почтением, будучи с Москве познакомлюсь при
AW> возможности с Michael Mackowsky ибо уменя есть практически вся
AW> сиситема ISIS-II от исходников , до всех приложеий и компиляторов

Voice: 395-2084

Best wishes! Michael KLUG