Hi people, I know that it is not advisable to send attached files to ML,
but this time I'll do it: many people seems to be interested on this
information, and it is a very small file (just 7K). Anyway I'll upload it
to my web page in one month or so.
Hasta incluso!
MegaSCSI incomplete BIOS reference
Compiled by Nestor Soriano (Konami Man), 1999
Get some MegaSCSI utilities from my web page:
http://konamiman.msx.tni.nl
...and/or ask me anything here:
[EMAIL PROTECTED]
1. PREVIOUS INTERISTING DATA
- The data contained here was extracted from the original japanese MegaSCSI
programming reference, but this document is not an exact translation work.
- If you want to check the presence of a MegaSCSI in a given slot, search the
string MEGASCSI in the address #7FE0 of the slot.
- All of the BIOS routines listed here must be called through an entry point
placed at address #7FCC on MegaSCSI addressing space. You can do this via
direct CALL or via interslot call.
- MegaSCSI can handle 8 DOS partitions and 16 extended partitions. DOS
partitions refers to those which have assigned a DOS drive letter and are
accessed via DOS funtion calls. Extended partitions can be accessed only via
MegaSCSI BIOS, and are used for example when performing floppy emulations.
- Each partition is described by an internal 16 byte partition table, which
can be read or written via BIOS functions #84 to #87. The format of this
table is as follows:
+0: Device ID. Bit b is placed to 1 when this partition is assigned to the
device with ID b. So this byte is %00000001 for ID 0, %00000010 for ID 1,
etc.
+1, bit 7: Disk change flag. It is 0 when a disk change was made but a disk
change status was not requested yet.
+1, bit 6: Write protection bit (1=write protected partition, 0=write enabled
partition). It is read and write bit.
+1, bits 0-5: unused, leave it to 0.
+2: Physical start sector, bits 23 to 16.
+3: Physical start sector, bits 15 to 8.
+4: Physical start sector, bits 7 to 0.
+5: Partition size in sectors, bits 23 to 16.
+6: Partition size in sectors, bits 15 to 8.
+7: Partition size in sectors, bits 7 to 0.
+8: Sector size in bytes, bits 15 to 8 (always #02).
+9: Sector size in bytes, bits 7 to 0 (always #00).
+10 to +15: Unused, leave it to zero.
- Error codes for these functions are as follows:
0: Write protected
2: Not ready
4: Data transfer error
8: Reservation conflict
10: Not supported media/Write error
12: Other error/Arbitration error
16: Format error
Some of these errors are SCSI specific. Refer here for the SCSI standard
programming reference:
http://scitexcd.com:8080/scsi2/Frames/
- MegaSCSI addressing space size is 32K, and it is divided into four 8K
banks:
Bank Control address
#4000-#5FFF #6000
#6000-#7FFF #6800
#8000-#9FFF #7000
#A000-#BFFF #7800
MegaSCSI SRAM is then divided also in 8K segments. You can connect any
segment to any bank by just sending the segment number to the control address
for the desired bank.
There is two connecting methods: read-only mode (for ROM emulation) and read
and write mode. Before sending to the control address, put bit 7 of the
segment number to 0 if you want to connect the segment in read-only mode,
else put this bit to 1.
2. BIOS FUNCTIONS LIST
* Reading SRAM capacity and use
Input: A = #A4
HL = Buffer address
Output: Buffer filled with the following information:
+0: Total amount of SRAM 8K segments.
+1: Number of SRAM banks used for DOS kernel. It is 2 for DOS 1
kernel, and 8 for DOS 2 kernel. DOS kernel start segment number is always 0.
+2: First bank number used for ESE-RAMdisk.
+3: Amount of banks used for ESE-RAMdisk.
* Setting SRAM use
Input: A = #A5
HL = Buffer addres, same format as #A4 funtion
Using these two functions you can reserve SRAM segments for your own use.
Just follow this procedure if you want to reserve N segments:
- Call function #A4.
- Add N to (BUFFER+2).
- Substract N from (BUFFER+3).
- Call function #A5.
- Format ESE-RAMdisk with ESFORM.COM.
Now ESE-RAMdisk is N*8K smaller, and you have N segments for your own use.
The number of the first reserved segment is 2 or 8, depending on the DOS
version of the kernel installed.
* Checking disk change status
Input: A = #10 + DOS partition number, or
#50 + extended partition number
HL = Pointer to Drive Parameter Block for the drive
Output: Cy = 1 if error
A = error code if Cy=1
B = 1 -> No disk change was performed
255 -> Disk was changed
0 -> Unknown disk status
Use DOS function ALLOC (#1B) in order to obtain the Drive Parameter Block
address.
* Reading/writing a partition table
Input: A = #84 for read a DOS partition table
#85 for set a DOS partition table
#86 for read a extended partition table
#87 for set a extended partition table
C = Partition number
HL = Source or destination buffer address for the partition table
Output: Cy = 1 if error
A = error code if Cy=1
If you set a new partition table, don't forget to put disk change bit to 0
first.
If you try to read the table for an undefined partition, you will get 0 for
the ID byte. If the partition contains actually the ESE-RAMdisk, the ID byte
will be 255. In both cases, all the other bytes for the partition table are
undefined.
* Creating a new partition
Input: A = #80 for creating a DOS partition, or
#82 for creating an extended partition
HL = Source buffer address for the partition table
Output: Cy = 1 if error
A = error code if Cy=1
C = number of the new created partition
If you can't create a new partition (8 DOS partitions or 16 extended
partitions are already defined) you will get error code 12.
Note that you will be able to access only the DOS partitions which are
actually assigned to MegaSCSI. For example if MegaSCSI has drives C:, D: and
E: assigned, then you can access only DOS partitions 0, 1 and 2 respectively.
Use ESET.COM in order to set the number of DOS drives controlled by MegaSCSI.
About the extended partitions, normally you will use them for emulating disk
image files. Use EP.COM for this.
* Freeing a partition
Input: A = #81 for free a DOS partition, or
#83 for free an extended partition
C = number of the partition to be freed
Output: Cy = 1 if error
A = error code if Cy=1
Note that even if you free a visible DOS partition, the assigned drive stills
reserved for MegaSCSI, but unusable. The only way to change the number of DOS
drives reserved to MegaSCSI is via ESET.COM.
* Sector read and write
Input: A = #00 + DOS drive number, or
#40 + extended partition number
Cy = 0 for read sectors
1 for write sectors
B = Number of sectors to be accessed
C = First sector number, bits 23 to 16
DE = First sector number, bits 15 to 0
HL = Source/destination buffer address for the data
Output: Cy = 1 if error
A = error code if Cy=1
B = number of sectors actually accessed
* SCSI command handler
Input: A = #C0
HL = Command packet buffer address
Output: Cy = 1 if error
A = error code if Cy=1
Command packet format is as follows:
+0: Device ID, same format as in the partition tables.
+1: Unused, leave it to 0.
+2, 3: Command Descriptor Block (CDB) buffer address.
+4, 5: Data transfer buffer address.
+6, 7: Status byte buffer address.
+8, 9: Message buffer address.
Refer here for the SCSI standard programming reference:
http://scitexcd.com:8080/scsi2/Frames/
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Konami Man - AKA Nestor Soriano (^ ^)v - Itsumo MSX user
New web address: http://konamiman.msx.tni.nl & http2//nestor.msx
[EMAIL PROTECTED] ICQ#: 18281450
Metal Gear for MSX - (C) Konami 1987 (Nothing new under the sun...)
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