The resident disk handler is separate from DOS and is part of the permanent operating system ROM. The disk handler does not use CIO.
The resident disk handler works with one sector at a time. It is used by setting the drive number, sector number, and operation code in the device control block. The program then jumps (JSR) to the handler entry vector, DSKINV [$E453 (58451)].
Device control block (for resident disk handler)
DDEVIC [$0300 (768)]
Serial bus I.D. Set by handler
DUNIT [$0301 (769)]
Drive number
DCOMND [$0302 (770)]
Command byte
DSTATS [$0303 (771)]
status byte
DBUFLO [$0304 (772)]
DBUFHI [$0305 (773)]
Pointer to 128 byte memory block for data storage.
DTIMLO [$0306 (774)]
Timeout value (response time limit) in seconds
DBYTLO [$0308 (776)]
DBYTHI [$0309 (777)]
number of bytes transferred, set by handler
DAUX1 [$030A (778)]
DAUX2 [$030B (779)]
sector number
Before the JSR to DSKINV is made the following parameters are set.
GET SECTOR parameters
DCOMND = $52 (82)
DUNIT = (1 - 4)
DBUFHI
and
DBUFLO = address of 128 byte buffer
DAUX1
and
DAUX2 = Sector number (LSB,MSB)
This operation will read the specified sector and put the data into the specified buffer.
PUT SECTOR is used the same as GET SECTOR except for DCOMND.
PUT SECTOR parameters
DCOMND = $50 (80)
This operation sends the data in the specified buffer to the specified disk sector.
PUT SECTOR WITH VERIFY is used the same as PUT SECTOR except for DCOMND.
PUT SECTOR WITH VERIFY parameters
DCOMND = $57 (87)
This operation sends the data in the specified buffer to the specified disk sector then checks for errors.
Only the DUNIT and DCOMND need to be set
GET STATUS parameters
DCOMND = $53 (83)
DUNIT = (1 - 4)
The status information will be put in three bytes starting at DVSTAT [$02EA (746)].
Status format
7 6 5 4 3 2 1 0
-----------------
DVSTAT + 0 | command stat |
-----------------
+ 1 | hardware stat |
-----------------
+ 2 | timeout value |
-----------------
The command status byte gives the following information.
Bit
0 1 = invalid command frame received
1 1 = invalid data frame received
2 1 = unsuccessful PUT operation
3 1 = disk is write protected
4 1 = active/standby
The hardware status byte contains the status register of the ISN1771-1 disk controller chip.
The timeout byte contains the maximum allowable response time for the drive in seconds.
The handler will format then verify the the disk. The numbers of all bad sectors (up to 63) will be put into the specified buffer followed by two bytes of $FF.
The following parameters are set before the call.
FORMAT parameters
DCOMND = $21 (33)
DUNIT = (1 - 4)
DBUFLO
and
DBUFHI = address of bad sector list (buffer)
After the operation the status byte is set. Also, DBYTLO and DBYTHI will contain the number of bytes of bad sector information (not including the two $FF bytes).
Useful data base variables and OS equates
DVSTAT $02EA,3 (746): device status block, 3 bytes
DDEVIC $0300 (768): serial bus I.D.
DUNIT $0301 (769): device number
DCOMND $0302 (770): command byte
DSTATS $0303 (771): status byte
DBUFLO $0304 (772): data buffer
DBUFHI $0305 (773): pointer
DTIMLO $0306 (774): timeout value
DBYTLO $0308 (776): number of bytes transfered
DBYTHI $0309 (777):
DAUX1 $030A (778): sector
DAUX2 $030B (779): number
DSKINV $E453 (58451): disk handler entry vector