Ciao Enrico,
non so se può essere utile ma in questo addendum spiega qualcosa come accedere
al settore 0 fisico (non logico)
Addendum for OPUS Discovery 2.22 Disassembly. Roelof Koning 1995/2007.
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A few remarks regarding the disassembly for version.2.2., as found on WOS.
-- About #0000 (Reset): This is an entry point where Opus pages in during a
Spectrum Reset. Not the address #0000 is stacked but address #0001 in order to
prevent an endless loop.
-- About #0048 (Key-Int ): This is an entry point where Opus pages in on every
interrupt. The fact that the return address is held in Table #0E opens the
possibility to extend the Interrupt Routine when a 6116 RAM is present.
-- At #0030 (Look-up) the disassembly says that 'B' holds the 'table-entry',
where later the tables concerned are called sub-tables, which they in fact are.
The 'table' in which 'B' is used is a sub table from the table of which the
number is given in the DEFB. The value in 'A' determines which subtable is
chosen.
-- At #1462 : DE is made to hold the default catalogue length, and not the
actual catalogue length as this is not copied into the disktable in RAM.
-- At #18E5 is byte 3 given as "extra sectors". In fact it is the starting
number for a sequence of sector numbers on a track, only relevant when
formatting.
-- At #18E5 is bytes 4-5 are given as "bootblock-1" where it should say 'number
of reserved sectors'.
-- At #18E5 is byte 7 given as 'control register' where it should say 'Command
Mask'. All commands for the FDC (WD1770) hold four bits for information
concerning hardware related issues. The bits give information about 'head
settling delay', 'write compensation', 'spin up sequence' etc., and must be
blended into every command code for the FDC. Such command of course goes into
the command register.
-- At #18E5: Byte 9 in the disk information table is unused.
-- At #1C3E : The 'lost-block' is not lost, nor stored in a specially reserved
block.
In fact it is the boot sector stored on the first sector on disk, which is
(hard) side 0,
track 0, sector 0. This 'absolute' sector 0 is not the 'logical' sector 0, as
(at least) one sector is 'reserved'. (Offset => 1)
Note that the number 65536 which is suggested for calculating the block number
of the bootsector is just 00000 (zero) in Machine Code. Which indeed is the
absolute number of the boot sector...... The whole exercise comes down to
subtracting the offset beforehand, so that when DOS adds the offset as usual
during the process, the final result is an absolute sector number and not a
logical one.
________________________________________
Da: zxspectrum-bounce@xxxxxxxxxxxxx <zxspectrum-bounce@xxxxxxxxxxxxx> per conto
di Enrico Maria Giordano <e.m.giordano@xxxxxxxxxxxxxxx>
Inviato: giovedì 28 giugno 2018 14:04
A: The ZX Spectrum Mailing-List
Oggetto: [zxspectrum] Re: Lettura parametri disco Opus
Il 28/06/2018 10:50, Enrico Maria Giordano ha scritto:
Secondo voi questa routine ha qualcosa che non va?
PRM CALL 5896
LD A,(DRV)
LD BC,0400H
CALL CPH
LD (BLK),HL
LD (CAT),DE
JP 5960
Se chiamata solo all'inizio del programma va tutto bene ma se la
richiamo durante l'esecuzione del programma allora succede qualcosa per
cui poi il programma stesso si blocca.
