CHAPTER 9
THE RESIDENT DISK HANDLER

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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

DISK HANDLER COMMANDS

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GET SECTOR

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.

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PUT SECTOR

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

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.

------------------------------------------------------------------------
GET STATUS

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.

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FORMAT DISK

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