SW1, Interrupter | CH Tech i4000 instruction

i4000 - Quad M-module carrier for VMEbus
User Manual	Version: 1.2

4.2.THE INTERRUPTER

The i4000 has a interrupter which is largely compatible with the MC68C153. The interrupter is a so called D08(O) type interrupter which means that the interrupter during an interrupt acknowledge cycle will put a status byte on the data lines D0-D7.

The interrupter uses a fixed interrupt level (IRQ1-IRQ7 set by SW1) for all M-modules. The i4000/NP2 also can be set to “software programmable level”, the interrupt level for an M-module has to be programmed using the control registers. Each M-module can generate its own vector.

L2	L1	L0	Interrupt level
on	on	on	software programmable level (only i4000/NP2)

on	on	off	level 1

on	off	on	level 2

on	off	off	level 3

off	on	on	level 4

off	on	off	level 5

off	off	on	level 6

off	off	off	level 7

There are two classes of interrupters which are both supported by the i4000: release on acknowledge (ROAK) or release on register access (RORA). The ROAK interrupter negates its interrupt request line in response to an interrupt acknowledge cycle. This mechanism will work with all handlers. The RORA interrupter releases its request when the handler accesses an on-board register during the interrupt service routine. The handler performs the acknowledge cycle but the interrupter does not immediately negate its request. Sometime during the service routine the handler will have to write to a register on the interrupter which causes it to negate the request.