ZX Spectrum and the hard drive - Article Vlad Sotnikova / Vega about work and programming of the hard drive (HDD) on the Spectrum.
Olden Z80
I am pleased to present the story of Vlad's capital
Sotnikova / Vega (St. Petersburg) of the phenomenon as a hard
drive on Spectrum. This subject is covered from all sides,
since the author - the best specialist in St. Petersburg
(except MOA:)) to have regards SMUC'a, I mean the device
allows to work with "gadgets" in the
benefit Speccy!
Now Vlad is working on the issue of connection to the
Spectrum CD-ROM, although what that's us! He is already
attached! But to CD-ROM fully earned, is required ff.
Information: ATAPI command list and description of the driver
CD-ROM (in any human or machine language) and also a good idea
to get the documentation to _not_ ATAPI CD-ROM'am - how they
work, team.
Waiting for information at the following addresses:
ZXNet: Vlad Sotnikov (500:812 / 08.9)
Fido: Vlad Sotnikov (2:5030 / 885.50)
If you do not have access to these networks, then
write to the editorial office, we will give
All Vlad.
__________________________________________
(C) Vlad Sotnikov / Vega, 2000
-= Spectrum and HDD =
1. Working with the hard drive on Spectrum'e.
1.1. Introduction.
1.2. Appeal to the hard drive.
1.3. Device hard drive.
1.4. Terminology.
1.5. Accessing the registry Scorpion'e.
1.6. Description of the registers.
1.7. Reading data from the hard drive.
1.8. Positioning the head.
1.9. Writing data to the hard drive.
1.10. Command Winchester.
1.11. Determination of the configuration Winchester.
2. The structure of the hard drive on the Scorpion.
2.1. File structure of the hard drive.
2.2. Structure description subsections.
2.3. The internal structure of the subsections.
2.4. How to run Is-Dos.
2.5. Structure of the sub-TR-DOS.
2.6. Sector Structure emulations.
2.7. The calculation of the checksum.
1. Working with the hard drive on Spectrum'e
Everything that is written here is based on
my personal experience, and therefore almost all of the
information is exclusive. As a consequence, the description can
meet inaccuracies or defects, for which apologize in advance.
1.1. Introduction
This article focuses on programming the hard disk, also
called "Winchester" on the computer Scorpion. On
Actually, if you have a hard drive connected
by another controller, then you just need to
know the port addresses of your controller, and
you with this article can learn
its programming.
Winchester - is an integral component of any computer,
especially now, when the amount of information in the hundreds
and even thousands of times larger than memory computers. Such
media as floppy disks, are losing their relevance. But despite
this, Spectrum has long been without the hard drive, and he
appeared only recently. K Unfortunately, the adaptation of the
hard drive to the system TR-DOS does not allow much
part of its capacity and therefore, working with them directly,
through the ports, you can not only a few times to increase
speed hard disk drive, but also to transform
it into an analog computer memory, as, indeed, made at a
computer as a PC.
1.2. Appeal to Winchester
So, to Winchester, please contact
in two ways. The first option - a request by
driver. On a PC, it is a program that allows you to see the
hard drive as storage for placing files in MS-DOS. On
Spectrum so the driver can be called
ProfPZU 4.01, which represents the hard disk as a collection of
images of TR-DOS floppies. Image connects to drive A, B, C or D
in terms of shadow monitor, and then the program works with one
of these carriers, not suspecting that instead of a floppy
disk, it communicates with the hard disk. This approach has
some drawbacks. In particular, it supports only appeal to the
TR-DOS through podgrogrammu # 3D13 (estestvenno!), and all
sorts of treatment such as # 3D2F lead to that the program is
on the TR-DOS hard drive image can not work. But it's not about
that.
In addition to contact through # 3D13 shadow monitor offers
an appeal to the hard drive via the command RST 8. I'm not one
here describe how it works can be found
in the book "SMUC, instructions on connecting
and work, v1.2 ". But the second version of
only increases the speed of reading and writing
data and, therefore, be called a full-fledged
can not.
1.3. Device hard drive
Winchester - a device that has
internal controller to read, write and process information.
Thus, the computer is not necessary to unscrew the drive and
perform these procedures - they take on a controller. Actually
programming the hard disk - is the transfer of his command, and
the transmission / reception of information from him.
Winchester is the next logical
internal structure: it exists
a number of cylinders. In each
cylinder has a certain amount of
heads. And each head has a certain number of sectors. If you
multiply all these values, we obtain the total number of
sectors (512 bytes) to your hard drive.
Dividing this number by 2, we know it
volume.
It goes without saying that the logical
structure of the hard drive has nothing to do with his actual
physical parameters. That is 16 heads does not mean that they
are in the hard drive is really 16. Usually physical heads 3-4,
while the number of sectors on each track varies,
as well as on CD-ROM. Nevertheless, to communicate with the
hard drive must be through its logical parameters, except
case when addressing mode is specified in
LBA (Logical Block Addressing), ie
Winchester instead of cylinder / head / sector
immediately indicates the relative address. But
LBA mode I have described here will not, because I do not know
exactly registers, where This 28-bit address is written.
These registers you can pick yourself.
As I recall, here they are: the registers of the cylinder
(both), the register of sectors, register drive / head
register, and opportunities (Same as the error register, only
record). Registers themselves are detailed below.
1.4. Terminology
Before starting the description let us agree on terms that
will be used by me in this article.
■ Logical address: consists of 3 values: the cylinder
number, head number and facilities sector.
■ Relative Address: 4-byte address
relatively early by the hard drive. Used in LBA mode. In the
logical address is converted to a logical address subroutine
SET_. At the Spectrum in the range 1.9 GB are used only 3 bytes.
■ Sector: hard drive it is 512
bytes. Therefore, under any sector referred to by me in this
article, you must understand the 512 bytes.
1.5. Accessing the registry Scorpion'e
Management controller is through registers. Each register in
controller SMUC corresponding port. He
will be indicated next to the register. Unfortunately, access
to these ports Scorpion in the computer should take place with
ROM included TR-DOS. Therefore, the record values in the port
will be as follows:
; OUT register A.
; In: [BC] - port number
; [A] - value to write to the port.
OUT_A LD IX, # 3FF0
PUSH IX
JP # 3D2F
The fact is that when accessing this
the memory automatically ROM TR-DOS and run the command
OUT (C), A.
Accordingly, reading:
; IN register A.
; In: [BC] - port number.
; Out: [A] - value read from the port.
IN_A LD IX, # 3FF3
PUSH IX
JP # 3D2F
Here is the same, only holds
Team IN A, (C).
In the following examples we will refer to these
subprograms. Knowing them, you can read and write ports
(Registers) hard drive. Below is a complete description of the
registers. Please note that the younger the register value is
always well # BE. It can be used to optimize code for speed
program.
1.6. Description of Registers
Command register (# FFBE)
Register just for the record. This register
contains the command code sent by the hard drive. Command
execution begins immediately after writing the register. It is
known that the command # E6 down the hard disc. Write:
LD A, # E6
LD BC, # FFBE
CALL OUT_A
RET
Your hard drive must stop.
Status register (# FFBE)
This register contains the drive status. The contents of
this register is updated after each command. Accordingly, the
bits of this register:
7 6 5 4 3 2 1 0
BSY DRDY DWF DSC DRQ CORR IDX ERR
- BSY (Busy). This bit is set immediately after the transfer
of command Winchester and is reset only after it
this team will perform. That is, bit set indicates that the hard
drive executes the command and you do not "hear".
- DRDY (drive ready). This
bit is set if the HDD is ready to take command.
- DWF (Prohibition of writing to disk). Bit indicates the
current state prohibition records (?).
- DSC (disk drive installation is completed).
Bit indicates that the drive heads are mounted on the track.
- DRQ (Data Request). Bit indicates
that the drive is ready to transfer a word or
byte of data between computers and storage.
- CORR (Corrected Data). Bit indicates that when reading
data occurred correction and data have been corrected.
- IDX (Index). Bit is set when
each revolution of the disc.
- ERR (Error). Bit indicates that the
During the previous command failed. More
to the cause of the error contained in
Register errors.
Most significant for us are
bits BSY, DRQ, and ERR. When a team to
hard drive requires the following steps:
1. Command is given (via the Command register).
2. We are waiting for removal of the signal BSY.
3. Enjoying a bit of ERR. If it is set - read the error
register and process error.
Let's write a subroutine that will be waiting for reset
signal BSY:
NO_BSY LD BC, # FFBE
CALL IN_A
RLCA
RET NC
JR NO_BSY
We run around in a loop as long as
BSY signal will not be withdrawn. Each team
must be terminated by an appeal to this routine.
Sub-validation errors:
ERR_ LD BC, # FFBE
CALL IN_A
RRCA
RET
If the output of the carry flag is set, the command was
executed with an error.
And our previous example, stopping the hard drive will look
like as follows:
LD A, # E6
LD BC, # FFBE
CALL OUT_A
CALL NO_BSY
CALL ERR_
JP C, ERROR ...
RET
So, now known as the fully
send a command to the hard drive. Below I give a subroutine
that does this.
; HDd Send Command.
; IN: [A] - command code.
; OUT: CY - Operation completed with error.
HDSC LD BC, # FFBE
CALL OUT_A; send command.
CALL NO_BSY; waiting for execution.
JP ERR_; look, there are no errors.
The following registers indicate the number of cylinders,
heads and sectors with which the operation occurs. So, when
reading these registers, we learn the place where the head.
When recording in the registers of other values of the head
does not change its position, but when doing a read / write, it
is positioned in accordance with values set in these
registers.
Register of the cylinder (the highest part) (# FDBE)
This register contains the high part of the initial cylinder
number for any disk operation. After the command this register
is modified, and always reflect the current cylinder number.
Elder cylinder number bits to be loaded into the register.
Register of the cylinder (the youngest part) (# FCBE)
This register contains the lower 8 bits of the initial
cylinder number for any disk operation. After issuing the
command This register is modified, and always reflects the
current cylinder number.
Register sector number (# FBBE)
This register contains the starting number
sector for every data operation. Sector number can be from 1 to
maximum number of sectors per track.
Register memory / Heads (# FEBE)
This register contains the number of heads and
drive. The contents of this register sets the number of the
drive and head number for command Initialize Drive Parameters.
7 6 5 4 3 2 1 0
1 LBA 1 DRV HS3 HS2 HS1 HS0
- DRV - drive selection bit. If
DRV = 0, then select drive 0, if the DRV = 1,
then select drive 1.
- LBA - bits indicate enabled or disabled LBA.
- HS3 ... HS0 contain binary numbers head (starting from
zero), which will selected. For example, if HS3 ... HS0 =% 0011,
will be selected head 3. HS3 - Senior
bits. After completion of the command this register
modified and always contains the current
number of the selected heads.
Fourth bit is very interesting. He sets the device slave \
master, with whom should operate the computer. So, if we
want to switch from the primary hard drive to a second,
parallel connection, then we need only set this bit and
record number in the register. All subsequent commands will
work with the selected device.
Sector count register (# FABE)
This register contains the number of transmitted data
sectors for read / record. A value of zero corresponds to 256
sectors.
When the command is read or
write sectors in this register records the number of sectors
that need to be send or receive. Next, it looks
as follows: we pass the byte
sector, and read the register counter sectors. The number in
this register will show the number of rough sectors. The number
0 indicates that the read / write completed.
Registry Errors (# F9BE)
This register contains the drive status, after the last
command or a diagnostic code.
After the completion of any command except Execute Drive
Diagnostic, this register contains the error code if bit ERR
in the status register is set (ERR = 1).
7 6 5 4 3 2 1 0
BBK UNC 0 0 IDNF ABRT TK0NF AMNF
- BBK (Bad Block Meeting). Bit indicates that when the
operation was received by the sector with the wrong label in
the header block of the sector.
- UNC (Uncorrectable Data Error).
Bit indicates that during the operation was
met with a fatal error in zone data.
- IDNF (Sector not found). Bit indicates that the title of
this sector is not found.
- ABRT (command aborted). Bit indicates that execution of a
given command was aborted due to an error state hard drive (not
ready yet, ban entry, etc.) or when an invalid command code.
- TK0NF (Track 0 not found). Bit
indicates that, under the command Recalibrate track 0 not found.
- AMNF (not found address marker). Bit
indicates that the address marker is not found
After finding the correct header sector.
- Unused bits are cleared.
Data register (the highest part) (# D8BE),
Data register (low part) (# F8BE).
1.7. Reading data from hard drive
Through the Data Register data exchange between computer and
hard drive. So, if we want to consider a sector with hard
drive, then we give the command "read". Further, the hard drive
reads one 512baytny sector in its buffer and waits. Then We
read the younger part of the sector, put in memory. Then older.
And so 256 times. It turns out 512 bytes. It is interesting
that among reading the bytes can be arbitrarily long pause -
the hard drive knows how many bytes we have taken. Then we read
the value of the register counter sectors. If the number is not
0, then repeat the cycle over again. Thus reads the sectors
from the hard drive. Below contains this subroutine. In HL
should be given a place in memory where the read
in A - the number of 512-byte sectors.
; Read the sector, given <HDSC>.
; IN: HL-buffer for reading, A-SECTORS
READ LD B, A
PUSH BC
LD BC, # FABE
CALL OUT_A
LD (BUF), HL
LD A, # 20
CALL HDSC; command to read ...
POP BC
READ1 PUSH BC
CALL READ_S; read Sector
POP BC
DJNZ READ1
RET
; READ Sector.
; Read sector ...
READ_S LD HL, (BUF)
LD BC, # 00BE
LD DE, # D8F8
READ_1 PUSH BC
LD B, E
CALL IN_A
LD (HL), A
INC HL
LD B, D
CALL IN_A
LD (HL), A
INC HL
POP BC
DJNZ READ_1
LD (BUF), HL
RET
BUF DS 2; Temporary variable for
store the address in memory
read / write.
1.8. Positioning the head
I think you have not forgotten that before calling the READ
command must specify the Winchester location from which to
read. This can be do the following routine:
; Write Cylinder, Head, Sector.
; Write to the cylinder number registers /
; Head / sector.
; IN: DE-cylinder, H-head, L-sector.
W_CHS LD BC, # FEBE
LD A, # A0; # B0 - slave.
XOR H
CALL OUT_A
DEC B
LD A, D
CALL OUT_A
DEC B
LD A, E
CALL OUT_A
DEC B
LD A, L
JP OUT_A
Subroutine that performs the opposite action, ie,
determining the position of head of the hard drive, will look
as follows:
; Read Cylinder, Head, Sector.
; Read the current cylinder / head / sector.
; OUT: DE-cylinder, H-head, L-sector.
R_CHS LD BC, # FEBE
CALL IN_A
AND # 0F
LD H, A
DEC B
CALL IN_A
LD D, A
DEC B
CALL IN_A
LD E, A
DEC B
CALL IN_A
LD L, A
RET
If you need to specify the relative address, you can use
subroutine SET_. For her work requires that
SECTOR cell was the number of sectors on the hard drive, and in
cell SH_SUM - product heads, and sectors.
; Install crown D, H, L.
; ADDRESS OFFSET - CIL / HED / SEC
; IN: D, H, L - 24-bit address.
; OUT: given the installation head.
SET_ LD (SET_3 +1), HL
LD HL, 0, E, H
LD A, D
OR A
JR Z, SET_1
LD D, L
SET_2 PUSH HL
PUSH DE
LD HL, # FFFF
LD DE, (SH_SUM)
PUSH AF
CALL DIV
POP AF, DE
INC HL
ADD HL, DE
EX DE, HL
POP HL
ADD HL, BC
DEC A
JR NZ, SET_2
SET_1 PUSH HL, DE
SET_3 LD HL, # 2121
LD DE, (SH_SUM)
CALL DIV
POP DE
ADD HL, DE
EX DE, HL
POP HL
ADD HL, BC
PUSH HL
EX DE, HL
LD DE, (SH_SUM)
CALL DIV
EX DE, HL
POP HL
ADD HL, BC
PUSH HL
EX DE, HL
LD A, (SECTOR)
LD D, 0, E, A
CALL DIV
LD H, C
INC L
POP DE
CALL W_CHS
RET
; Division. <>
DIV LD A, E
OR D
RET Z
XOR A
LD C, A, B, A
EX DE, HL
DIVW1 INC B
BIT 7, H
JR NZ, DIVW2
ADD HL, HL
JR DIVW1
DIVW2 EX DE, HL
DIVW3 OR A
SBC HL, DE
JR NC, DIVW4
ADD HL, DE
DIVW4 CCF
RL C, A
RR D, E
DJNZ DIVW3
LD B, A
RET
SH_SUM DB heads * sectors.
SECTOR DB number of sectors.
1.9. Writing data to a hard drive
To record information on a hard drive,
you must install the head using
sub W_CHS or SET_ and perform
following routine:
; Writing sector, given <HDSC>.
; IN: HL-buffer for writing, A-SECTORS
WRITE LD B, A
PUSH BC
LD BC, # FABE
CALL OUT_A
LD (BUF), HL
LD A, # 30
CALL HDSC; team to write ...
POP BC
WRITE1 PUSH BC
CALL WRITE_S
POP BC
DJNZ WRITE1
RET
; WRITE Sector.
; Write sector ...
WRITE_S LD HL, (BUF)
LD BC, # 00BE
LD DE, # D8F8
WRITE_1 PUSH BC
LD B, D
INC HL
LD A, (HL)
CALL OUT_A
LD B, E
DEC HL
LD A, (HL)
CALL OUT_A
INC HL
INC HL
POP BC
DJNZ WRITE_1
LD (BUF), HL
RET
1.10. Command Winchester
Below I will provide a list of commands relevant when
working with the hard drive on the Spectrum.
Identify Drive (# EC)
(Identify Drive)
After the team must wait for the installation DRQ signal and
perform routine READ_S, pre-recorded in cell (BUF) address in
memory where the read data on your hard drive. Here are the
most important:
2 - number of cylinders (2 bytes);
6 - number of heads (2 bytes);
12 - number of sectors (2 bytes);
20 - serial number (20 characters);
+40 - Buffer type hard drive (2 bytes);
42 - Buffer size in sectors (2 bye
ma);
+46 - Firmware (8 characters);
54 - model name (40 characters).
This number of heads, sectors and cylinders, in most cases
turn out to be false. In addition, all textual information is a
custom format. First is the high byte, and then junior. To make
it readable kind of need to change the first byte of the second,
the third with the fourth, etc.
The whole text is left-aligned and
padded with spaces. In case the first
bytes of text - 0, then the name is not defined.
The buffer type is the hard drive:
0 - not defined.
1 - Single Buffering, Winchester
can not perform simultaneous read and write operations.
2 - double buffering. Winchester can simultaneously read
and write information.
3 - double buffering, in addition
reading is carried out with caching.
The cell size of the buffer indicates which
volume has an internal buffer hard drive.
The larger the buffer size, the higher the rate of
exchange of data between hard disk and the computer.
Idle (# 97, # E3, # 95, # E1)
(Go to the passive mode)
Occurs stop the hard drive to the next command.
Recalibrate (# 1x)
(Recalibration)
This command moves the head read /
records from any location in the disk at cylinder 0.
If the drive can not install head
zero-cylinder, generating an error
"Track Not Found" (Track Not Found).
Read Sector (s) (# 20)
(Read sector (s))
Write Sector (s) (# 30)
(Write Sector (s))
Work teams described above.
Sleep (# 99, # E6)
(Stop)
Winchester is completely stopped.
The only way to get your hard drive
Stop mode without powering down
Hardware and software reset is
reset.
Standby (# 96, # E2, # 94, # E0)
(Standby)
This command takes the hard disk into standby mode. If the
disc is already stopped, then sequence of stopping drive fails.
1.11. Determination of the hard drive configuration
I also want to talk about how I
managed to write a subroutine that determines the true the
logical geometry of the hard drive.
It is well known, and I'm here to write about it
that logical hard disk geometry
You can read from the sector caused by
team Identify Drive, and it does so the Shadow Monitor option
Auto Detect Hard Disk. But 25% of cases, this information
turns out to be wrong.
How do you know the real meaning of cylinders / heads /
sectors of your hard drive? After all, rely on the words the
seller from whom you buy this hard drive is very unreliable.
My own idea is very simple: let's say you
give the hard drive, click to read 256
sectors. Reads one sector (sub READ_S). Now, in the registers
of the cylinder / head / sectors recorded values following
the order in Gaza. That is the number of the sector increased
by 1. Read the next sector. And as soon as
sector to take the value 1 and increased number of heads, then
the previous value sector and there are a number of sectors on
the disk. Same with the heads (wait until the head is not to
take the value 0 and increased number of sectors). Since the
cylinders more complicated, but, on the other hand, if we work
within existing subdivisions, to know the maximum number of
cylinders does not necessarily - beyond the hard drive you do
not quit. Nevertheless, to determine the number of cylinders it
is possible - for example, reading 0 and head 1 sector each
cylinder until it fails, then there is still the sector will
not be found.
Presented here the software automatically determines the
number of heads and sectors on the disk. The label should TABL
indicate a 512-byte buffer.
, Automatic configuration of screw.
; OUT: [H] - HEADS.
; [L] - SECTORS.
A_CONF LD DE, 0
LD H, D
LD L, E
CALL W_CHS
LD A, # EC
CALL HDSC
LD BC, # FFBE
CALL IN_A
OR A
RET Z; device does not
CALL R_CHS
OR A
LD HL, # EB14
SBC HL, DE
RET Z; a CD-ROM
CALL NO_BSY
LD DE, 0
LD HL, # 0002
CALL W_CHS
LD A, 65
LD BC, # FABE
CALL OUT_A
LD A, # 20
CALL HDSC
CALL NO_BSY
LD BC, # FBBE
A_CONF2 PUSH BC
CALL IN_A
LD D, A
PUSH DE
LD BC, # FFBE
A_CONF3 CALL IN_A
BIT 3, A
JR Z, A_CONF3
LD HL, TABL
LD (BUF), HL
CALL READ_S
CALL NO_BSY
POP DE
POP BC
CALL IN_A
SUB D
JR NC, A_CONF2
LD A, D
PUSH AF
LD (A_CONFS-1), A
LD A, 1
LD (A_CONFS), A
A_CONFS EQU $ +2
LD HL, # 0100
LD DE, 0
CALL W_CHS
LD A, 2
LD BC, # FABE
CALL OUT_A
LD A, # 40
CALL HDSC
CALL NO_BSY
LD BC, # FEBE
CALL IN_A
LD HL, A_CONFS
AND 15
OR A
JR Z, A_CONFH
INC (HL)
JR A_CONFS-2
A_CONFH LD A, (HL)
INC A
LD H, A
POP AF
LD L, A
RET
2. The structure of hard disk partitioning
Scorpion on a computer
The system MS-DOS programs for the Spectrum, of course, to
work without some and very time-consuming adaptation can not.
Required to create a hard disk system TR-DOS. The authors of
the Shadow Monitor approached this problem fairly original: on
the hard drive creates a sequence of TR-DOS disk images, and
each of these images can be "connected" to the carrier A, B, C
or D and the operating system TR-DOS will work with this way,
not knowing that it's not a real disk. Hence it is the
terminology: drive physical (floppy diskette drive), and
emulated drive (HDD-image).
2.1. File structure Winchester
Structural organization of accommodation on
hard drive information is as follows
manner.
1. Will create a global sub-wearing always the name of MFS
(MOA File System?). Shadow Monitor will work only with him. In
addition to this subsection to hard drive can be sub-
other operating systems. Thus,
one hard drive can be used on
Spectrum and other computers.
2. Within the global sub-creates the so-called local
sections. They may be the following:
- TR-DOS. This section contains a sequence of TR-DOS disk
images (1 to 51).
- MicroDos. As the author wrote of the Shadow
Monitor this subsection is reserved
for compatibility with PCs that use this
OS and application support for this sub-section planned to
write in the future. But so far nothing written and was not.
- IS-DOS. Subdivision for the OS with the same name.
- BAD. With the help of this subsection to
Winchester covers an area that has
bad sectors.
Ways to work with this structure, the hard drive via the
menu of the Monitor and the Shadow subroutine RST 8 are quite
diverse. Here I will describe how this
structure looks like from the inside. "
2.2. Subsections describe the structure
List of global sub is 0 for the sector (0 cylinder
0 head 1 sector) at # 01BE, and
occupies 16 bytes, where:
0 - At MOA 0.
1 - head |
2 - Sector | beginning
3 - cylinder (?) | Subdivision.
4 - at MOA # 53 - MFS.
5 -?
6 -?
7 -?
+8 |
+9 | Relative address
+10 | Subdivision.
+11 |
+12 |
+13 | Length sub
+14 | (In sectors).
+15 |
Total number of such descriptors can be 4.
Fourth byte # 53 - a sign of sub-
MFS. Meaning 5, 6 and 7 of the byte I guess so and failed.
Also, I'm not quite sure of the meaning third byte.
Nevertheless, 2 nd and third bytes indicate the location
list of local subdivisions.
It takes 2 sector (1024 bytes).
Description of each subsection is 16
bytes as follows.
0 - type of sub-section:
1 - TR-DOS.
2 - MicroDos.
3 - Is-DOS.
4 - BAD.
+1 |
+2 | Relative address
+3 | Subdivision.
+4 |
+6 |
+7 | Length sub
+8 | (In sectors).
+9 |
10 - Name of sub-section (6 characters).
With the 4-byte relative address, we can turn to the top of
any local subdivision.
2.3. The internal structure of sub-
Subsections MicroDos and BAD internal
structures do not have. Subdivision IS-DOS such
structure has, but she is determined entirely just this
operating system. Here I will only tell you how to run the
IS-DOS, located on the hard drive.
2.4. How to run IS-DOS
The launch will take place with the help of sub RST 8. To do
this, run the following routine:
LD DE, name of the subkey *
LD A, 15; connect to the drive "D"
LD H, A; glitch MOA: SET 4, (HL)
LD C, 35
RST 8
DB # 81
LD HL, buffer for 1 sector.
PUSH HL
LD BC, # 0124, read 1 sector.
LD DE, 1
RST 8
DB # 81
POP HL
LD A, (HL)
CP # 18; jr $+... ?
RET NZ; nezapuskaemy IS-DOS
JP (HL); launched
I note that in some cases, IS-DOS starts incomplete. What
this case: whether the stack, whether in kakoylibo installed
wrong page - to determine yourself.
2.5. Structure of the sub-TR-DOS
Now consider the sub-TR-DOS. He
is one of the central sub-
on the hard drive, because most programs work with this
operating system. Therefore, we consider it in detail.
Structure of the sub is as follows: in the first two sectors is
a description of TR-DOS disk images. Description absolutely
similar in structure to the description of the local drives.
Each disk is described 16 bytes, where 0 - is always 1 (TR-DOS),
1 - e disk image, plus 1, 6 - length of the disc (always 1, 5,
0, 0 - as length of the TR-DOS image is strictly fixed:
1280 a 512-byte sectors), 10 - name
disc. Standard name - Disk??, Where? -
serial number of the disk, but it can be painless for the
Shadow Monitor change.
Please note that the address drive
on the hard drive to add 1 sector. The fact is that before each
disc unclear why there is a 512-byte region filled with zeros.
I also want to draw attention to the maximum number of disk
images in TR-DOS section. I've an opinion that there may be
more than 51. Explain what is misleading: the fact that the
Shadow Monitor for Treatment to the disks inside the sub uses a
16-bit register. With respect to the sub-address 51-second
drive to be # FF33, and the address of 52-second drive would
have been # 010434. That is why the maximum number of drives in
the subsection - 51.
2.6. Sector Structure emulations
Each subsection or a disk image can be
connected to a driver A, B, C or D. Information about the
emulation is in 2 relative to the sector if the Shadow Monitor
does not work in LBA mode, and 3 relative to the sector, if the
flag is LBA enabled. Her length - 1 sector. Each disc is
described by 22 Bytes:
0 - type of sub-section (0 - no emulation).
+1 |
+2 | Disk address / subdivision.
+3 |
+4 |
5 - the type of subdivision.
+6 |
+7 | Length CD / subsection.
+8 |
+9 |
10 - Name of sub-section (6 bytes).
16 - drive name / subsection (6 bytes).
If we connect the disk image, then 10 will be the name of
the subsection, and 16 - the name of a disk image (Disk01 and
the like). If not connected to TR-DOS sub-section, then
16 will be addressed in sub-section (ie the same
as in 10).
To fully connect the drive or
subkey, follow these
steps:
1. Connect the emulation via RST 8. Emulation prescribe an 8
page.
2. Consider the sector from the hard drive emulation.
3. Change the emulation drive.
4. Record CRC in the sector emulation.
5. Save this sector on the hard drive.
It is very important when the simulation to calculate the
checksum. If while reading this the shadow Monitor checksum
does not match, then he would withdraw emulation of all four
discs.
To calculate the correct checksum, must do the following:
LD DE, sector in the memory.
LD BC, 508
CALL CRC
LD HL, sector + 508.
LD (HL), E
INC HL
LD (HL), D
RET
2.7. Checksum calculation
The code below courtesy of the CRC to me MOA and is a
himself, as he explained to me, "hybrid" CRC-16
and CRC-32.
; Cyclic Redundancy Check.
; Calculation of the checksum.
; IN: [DE] - START, [BC] - LENGHT
; OUT: [DE] - CRC-SUMM.
CRC LD HL, # FFFF
PUSH IX
PUSH DE
POP IX
EX DE, HL
CRC_1 LD HL, CRC_TAB
LD A, (IX)
INC IX
XOR E
ADD A, L
LD L, A
JR NC, CRC_2
INC H
CRC_2 LD A, D
XOR (HL)
LD E, A
INC HL
XOR A
XOR (HL)
LD D, A
DEC BC
LD A, C
OR B
JR NZ, CRC_1
POP IX
RET
CRC_TAB DW # 0000, # 1021, # 2042, # 3063
DW # 4084, # 50A5, # 60C6, # 70E7
DW # 8108, # 9129, # A14A, # B16B
DW # C18C, # D1AD, # E1CE, # F1EF
DW # 1231, # 0210, # 3273, # 2252
DW # 52B5, # 4294, # 72F7, # 62D6
DW # 9339, # 8318, # B37B, # A35A
DW # D3BD, # C39C, # F3FF, # E3DE
DW # 2462, # 3443, # 0420, # 1401
DW # 64E6, # 74C7, # 44A4, # 5485
DW # A56A, # B54B, # 8528, # 9509
DW # E5EE, # F5CF, # C5AC, # D58D
DW # 3653, # 2672, # 1611, # 0630
DW # 76D7, # 66F6, # 5695, # 46B4
DW # B75B, # A77A, # 9719, # 8738
DW # F7DF, # E7FE, # D79D, # C7BC
DW # 48C4, # 58E5, # 6886, # 78A7
DW # 0840, # 1861, # 2802, # 3823
DW # C9CC, # D9ED, # E98E, # F9AF
DW # 8948, # 9969, # A90A, # B92B
DW # 5AF5, # 4AD4, # 7AB7, # 6A96
DW # 1A71, # 0A50, # 3A33, # 2A12
DW # DBFD, # CBDC, # FBBF, # EB9E
DW # 9B79, # 8B58, # BB3B, # AB1A
DW # 6CA6, # 7C87, # 4CE4, # 5CC5
DW # 2C22, # 3C03, # 0C60, # 1C41
DW # EDAE, # FD8F, # CDEC, # DDCD
DW # AD2A, # BD0B, # 8D68, # 9D49
DW # 7E97, # 6EB6, # 5ED5, # 4EF4
DW # 3E13, # 2E32, # 1E51, # 0E70
DW # FF9F, # EFBE, # DFDD, # CFFC
DW # BF1B, # AF3A, # 9F59, # 8F78
DW # 9188, # 81A9, # B1CA, # A1EB
DW # D10C, # C12D, # F14E, # E16F
DW # 1080, # 00A1, # 30C2, # 20E3
DW # 5004, # 4025, # 7046, # 6067
DW # 83B9, # 9398, # A3FB, # B3DA
DW # C33D, # D31C, # E37F, # F35E
DW # 02B1, # 1290, # 22F3, # 32D2
DW # 4235, # 5214, # 6277, # 7256
DW # B5EA, # A5CB, # 95A8, # 8589
DW # F56E, # E54F, # D52C, # C50D
DW # 34E2, # 24C3, # 14A0, # 0481
DW # 7466, # 6447, # 5424, # 4405
DW # A7DB, # B7FA, # 8799, # 97B8
DW # E75F, # F77E, # C71D, # D73C
DW # 26D3, # 36F2, # 0691, # 16B0
DW # 6657, # 7676, # 4615, # 5634
DW # D94C, # C96D, # F90E, # E92F
DW # 99C8, # 89E9, # B98A, # A9AB
DW # 5844, # 4865, # 7806, # 6827
DW # 18C0, # 08E1, # 3882, # 28A3
DW # CB7D, # DB5C, # EB3F, # FB1E
DW # 8BF9, # 9BD8, # ABBB, # BB9A
DW # 4A75, # 5A54, # 6A37, # 7A16
DW # 0AF1, # 1AD0, # 2AB3, # 3A92
DW # FD2E, # ED0F, # DD6C, # CD4D
DW # BDAA, # AD8B, # 9DE8, # 8DC9
DW # 7C26, # 6C07, # 5C64, # 4C45
DW # 3CA2, # 2C83, # 1CE0, # 0CC1
DW # EF1F, # FF3E, # CF5D, # DF7C
DW # AF9B, # BFBA, # 8FD9, # 9FF8
DW # 6E17, # 7E36, # 4E55, # 5E74
DW # 2E93, # 3EB2, # 0ED1, # 1EF0
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Other articles:
ZX Spectrum and the hard drive - Article Vlad Sotnikova / Vega about work and programming of the hard drive (HDD) on the Spectrum.
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