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Docs » Autodocs » disk.resource » GetUnit
GetUnit - allocate the disk for a driver
lastDriver = GetUnit( unitPointer ), DRResource
D0 A1 A6
struct DiscResourceUnit *GetUnit(struct DiscResourceUnit *);
This routine allocates the disk to a driver. It is either
immediately available, or the request is saved until the disk
is available. When it is available, your unitPointer is
sent back to you (via ReplyMsg). You may then reattempt the
GetUnit.
Allocating the disk allows you to use the disk's resources.
Remember however that there are four units to the disk; you are
only one of them. Please be polite to the other units (by never
selecting them, and by not leaving interrupts enabled, etc.).
When you are done, please leave the disk in the following state:
dmacon dma bit ON
dsklen dma bit OFF (write a #DSKDMAOFF to dsklen)
adkcon disk bits -- any way you want
intena:disk sync and disk block interrupts -- Both DISABLED
CIA resource index interrupt -- DISABLED
8520 outputs -- doesn't matter, because all bits will be
set to inactive by the resource.
8520 data direction regs -- restore to original state.
NOTE: GetUnit() does NOT turn on the interrupts for you.
You must use AbleICR (for the index interrupt) or intena
(for the diskbyte and diskblock interrupts) to turn them
on. You should turn them off before calling GiveUnit,
as stated above.
unitPtr - a pointer you your disk resource unit structure.
Note that the message filed of the structure MUST
be a valid message, ready to be replied to. Make sure
ln_Name points to a null-terminated string, preferably
one that identifies your program.
You need to set up the three interrupt structures,
in particular the IS_DATA and IS_CODE fields. Set them
to NULL if you don't need that interrupt. Also, set
the ln_Type of the interrupt structure to NT_INTERRUPT.
WARNING: don't turn on a disk resource interrupt unless
the IS_CODE for that interrupt points to executable code!
IS_CODE will be called with IS_DATA in A1 when the
interrupt occurs. Preserve all regs but D0/D1/A0/A1.
Do not make assumptions about A0.
lastDriver - if the disk is not busy, then the last unit
to use the disk is returned. This may be used to
see if a driver needs to reset device registers.
(If you were the last user, then no one has changed
any of the registers. If someone else has used it,
then any allowable changes may have been made). If the
disk is busy, then a null is returned.
EXCEPTIONS
GiveUnit()
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