Motorola BUsing Interrupts on the MVME172, VMEchip2 Tick Timer 1 Periodic Interrupt Example

BUsing Interrupts on the MVME172

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Introduction

This appendix demonstrates how to use interrupts on the MVME172. It gives an example of how to generate and handle a VMEchip2 Tick Timer 1 interrupt on an MVME172 that has a VMEbus connection. Specific values have been given for the register writes.

Read this entire appendix before performing any of these procedures.

VMEchip2 Tick Timer 1 Periodic Interrupt Example

1.Set up Tick Timer:

Step	Register and Address	Action and Reference
1	Prescaler	If not already initialized by the
	Control Register	debugger, initialize as follows:
	$FFF4004C	Prescaler Register = 256 - Bclock
		(MHz). This gives a 1 MHz clock
		to the tick timers. Bclock is the
		bus clock rate, such as 25 MHz.
		256 - 25 = $E7.
2	Tick Timer 1	For periodic interrupts, set the
	Compare Register	Compare Register value = Period
	$FFF40050	(s). For example, if you want an
		interrupt every millisecond, set
		the register value to 1000 ($3E8).
		Refer to the Tick Timer 1
		Compare Register description in
		Chapter 2.
3	Tick Timer 1	Write a zero to clear.
	Counter Register
	$FFF40054

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