Disk ROM
This page was last modified 17:20, 7 April 2018 by NYYRIKKI.
4010H (DISKIO) (See PHYDIO in main BIOS)
Function:	Physical input/output for disk devices
Input:  [F]     carry set for write
                carry reset for read
        [A]     Drive number (0=A:)
        [B]     Number of sectors to read/write
        [C]     Media descriptor
        [DE]    Logical sector number (starts at 0)
        [HL]    Transfer address

Output: [F]     carry set on error
                carry reset on success
        [A]     If error: errorcode
        [B]     Number of sectors transferred (always)

Error codes in [A] can be:
        0       Write protected
        2       Not ready
        4       Data (CRC) error
        6       Seek error
        8       Record not found
        10      Write fault
        12      Bad parameter
        14      Out of memory
        16      Other error
4013H (DSKCHG)
Function:	Check if disk has been changed.
Input:  [A]     Drive number (0=A:)
        [B]     Media descriptor
        [C]     Media descriptor
        [HL]    Base address of DPB

Output: [F]     carry set on error
                carry reset on success
        [A]     If error: errorcode (see DSKIO)
        [B]     if success: 1=Disk not changed, 0=Unknown, -1=Disk changed

Note:   If the disk has been changed or may have been changed (unknown) read
        the boot sector or the FAT sector for a disk media descriptor and
        transfer a new DPB as with GETDPB
4016H (GETDPB)
Function:	Get Drive Parameter Block
Input:  [A]     Drive number
        [B]     First byte of FAT (media descriptor)
        [C]     Media descriptor
        [HL]    Base address of DPB

Output: [HL+1] .. [HL+18] = DPB for specified drive

Note:   DPB consists of

Name   Offset Size Description
----------------------------------------------------------------------------
MEDIA    0     1   Media type (F8..FF)
SECSIZ   1     2   Sector size (must be 2^n)
DIRMSK   3     1   (SECSIZE/32)-1
DIRSHFT  4     1   Number of one bits in DIRMSK
CLUSMSK  5     1   (Sectors per cluster)-1
CLUSSHFT 6     1   (Number of one bits in CLUSMSK)+1
FIRFAT   7     2   Logical sector number of first FAT
FATCNT   8     1   Number of FATs
MAXENT   A     1   Number of directory entries (max 254)
FIRREC   B     2   Logical sector number of first data
MAXCLUS  D     2   (Number of clusters (not including reserved, FAT and
                   directory sectors))+1
FATSIZ   F     1   Number of sectors used
FIRDIR   10    2   FAT logical sector number of start of directory
4019H (CHOICE)
Funtion:	Get string that describes disk formatting options.
Input:	None
Output:	[HL]    Address of zero terminated character string (ASCIIZ) with
                the text with choices for a DSKFMT
                If there is no choice (only 1 format supported) return [HL]=0
401CH (DSKFMT)
Function:       Format disk
Input:  [A]     Choice specified by user (1-9). See CHOICE
        [D]     Drive number (0=A:)
        [HL]    Begin address of work area
        [BC]    Length of work area
Output: [F]     Carry flag reset on success
                Carry flag set on error (see DISKIO for error codes)

Notes:  Also writes a MSX boot sector at sector 0, clears all FATs (media
        descriptor at first byte, 0FFh at second/third byte and rest zero)
        and clears the directory (filling it with zeros)
401FH (DSKSTP)
Function:	Stop all local drives
Input:		None
Output:		None
4022H
Function:	Start DiskBASIC
Input:		None
Output:		None (Does not return)
4025H
Function:	Format disk using custom buffer
Input:		[HL]	Start of buffer
		[BC]	Size of buffer
Output:		None
Note:	This is interactive process with user
4029H
Function:	Stop all drives on all controllers
Input:		None
Output:		None
Note:	Bad idea: This will stop floppy drive motors and power off HDD
	motors. (Do not start again automatically) Devices like CD-ROM 
	and Zip-drives usually handle stop commands as eject requests.
402DH (GETSLT)
Function:	Get slotID of disk ROM
Input:		None
Output:	[A]	SlotID
4030H
Function:	Get MSX-DOS system bottom
Input:		None
Output:	[HL]	Lowest address used by the base MSX-DOS system