GetUnit

allocate the disk for a driver

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 - entena:disk sync and disk block interrupts -- Both DISABLED - CIA resource index interrupt -- DISABLED - 8520 outputs. It doesn't matter, because all bits will be

• 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.

GiveUnit