Cache Coherency (MVME167P)

Periodic Tick Timer 1 interrupts now occur, so you need an interrupt handler. Section 3 gives the details, as follows.

3.Set up an interrupt handler routine:

Step

Action and Reference

 

 

Your interrupt handler should include the following features.

1Be sure the MC680x0 Vector Base register is set up. Set the proper MC680x0 exception vector location so the processor vectors to your interrupt handler location. You can determine the proper exception vector location to set from the MC680x0 Vector Base register, the VMEchip2 Base register, and Table 2-4, Local Bus Interrupter Summary in Chapter 2, from which you can determine the actual interrupt vector given on a Tick Timer 1 interrupt. Lower the MC680x0 mask so the interrupt level you programmed is accepted. The interrupt handler itself should include the following (steps 2 through 5).

2Confirm that the Tick Timer 1 interrupt occurred, by reading the status of bit 24 in the Interrupter Status register at $FFF40068. A high indicates an interrupt present.

3Clear the Tick Timer 1 interrupt by writing a 1 to bit 24 of the Interrupt Clear register at $FFF40074.

4Increment a software counter to keep track of the number of interrupts, if desired. Output a character or some other action (such as toggling the FAIL LED) on an appropriate count, such as 1000.

5Return from exception.

1

Cache Coherency (MVME167P)

The MVME167P’s MC68040 processor has the ability to watch Local Bus cycles executed by other Local Bus masters such as the SCSI DMA controller, the LAN controller, the VMEchip2 DMA controller, and the VMEbus-to-Local-Bus controller. This bus snooping capability is described in the M68040 Microprocessors User’s Manual sections on Cache Coherency and Bus Snooping Operation.

When snooping is enabled, the MC68040 MPU can source data and invalidate cache entries as required by the current cycle. The MPU cannot watch VMEbus cycles that do not access the Local Bus. Software must

http://www.motorola.com/computer/literature

1-49

Page 75
Image 75
Motorola MVME1X7P manual Cache Coherency MVME167P