IBM PC 300PL manual Hard disk drives and controller, Software compatibility, Software interrupts

Chapter 6. System compatibility

4.Waits one I/O delay

5.Enables the interrupt through the Set Interrupt Enable Flag command

Hardware interrupt IRQ9 is defined	as the	replacement interrupt	level	for the cascad
Program interrupt sharing is implemented	on IRQ2, interrupt hex 0A.		The	following processing
maintain compatibility with the IRQ2	used by	IBM Personal Computer	products:

1. A device drives the interrupt request active on IRQ2 of the channel.

2. This interrupt request is mapped in hardware to IRQ9 input on the second interrupt

3.When the interrupt occurs, the system microprocessor passes control to the IRQ9 ( interrupt handler.

4. This interrupt	handler performs	an EOI command to the second interrupt controller and
to the IRQ2	(interrupt hex 0A)	interrupt handler.

5. This IRQ2 interrupt handler, when handling the interrupt, causes the device to rese request before performing an EOI command to the master interrupt controller that fini the IRQ2 request.

Hard disk drives and controller

Reading from and writing to the hard disk is initiated in the same way as in IBM Pe products; however, new functions are supported.

Software compatibility

To maintain software compatibility, the interrupt polling mechanism that is used by IBM P products is retained. Software that interfaces with the reset port for the IBM Pers positive-edge interrupt sharing (hex oraddress06Fx, where02Fx is the interrupt level) does not creat interference.

Software interrupts

With the

advent

of

software interrupt sharing, software interrupt routines must daisy

routine must check the function value, and

if

it is

not in

the range of function calls

transfer

control

to

the next routine in the chain. Because

software

interrupts

are ini

address

0:0

before

daisy chaining,

check

for

this

case.

If

the

next routine

is

poin

the

function

call

is

out of range,

the appropriate

action

is

to

set

the carry

flag

an

error

condition.

Machine-sensitive programs

Programs		can select machine-specific features, but	they must first identify the	machine
IBM	has	defined methods for uniquely determining	the specific machine type. The machin
can	be	found through Interrupt 15H, Return System	Configuration Parameters function	(AH)=C0

24 Technical Information Manual