68k interrupts: Difference between revisions

Revision as of 12:53, 27 June 2011

There are 3 interrupt levels on the AES and MVS. Only 2 on the CD hardware.

Interrupts need to be acknowledged by writing to register $3C000C (REG_IRQACK).

bit2: Ack VBlank interrupt
bit1: Ack Timer interrupt
bit0: Ack level 3

move	#$0007,REG_IRQACK     ; Acknowledge all interrupts

Bits 8~10 of the SR register are used to mask them.

move	#$2000,SR     ; Enable all interrupts (+Supervisor mode)
move	#$2700,SR     ; Disable all interrupts (+Supervisor mode)

Vertical Blank interrupt

The VBlank interrupt is almost always used. It occurs everytime a new frame is traced (~60Hz). See display timing.

Timer interrupt

The Timer interrupt's behavior can be programmed through the GPU's memory mapped registers. It is made of a down-counting 32bit register clocked by the 6MHz pixel clock, and a corresponding set register. When the counter reaches 0, an interrupt is generated. Intervals can range from 166.7µs to 11.9 minutes (?). The Sammy logo at the start of Viewpoint is an example of its use. Sengoku 3 and Neo Turf Masters are also known to rely on them to do scanline effects.

AES/MVS interrupts levels

VBlank: Level 0
Timer: Level 1
Pending at startup ?: Level 2

CD interrupts levels

VBlank: Level 1
Timer: Level 0

@@ Line 21: / Line 21: @@
 The VBlank interrupt is almost always used. It occurs everytime a new frame is traced (~60Hz). See [[display timing]].
-== Timer interrupt ==
+== [[Timer interrupt]] ==
-The Timer interrupt's behavior can be programmed through the [[GPU]]'s [[memory mapped registers]]. It is made of an up-counting 32bit counter clocked by the 6MHz pixel clock, and a match register. It can be used to generate interrupts at intervals ranging from 166.7µs to 11.9 minutes (?). The Sammy logo at the start of [[Viewpoint]] is an example of its use. [[Sengoku 3]] and [[Neo Turf Masters]] are also known to rely on them to do [[scanline effects]].
+The Timer interrupt's behavior can be programmed through the [[GPU]]'s [[memory mapped registers]]. It is made of a down-counting 32bit register clocked by the 6MHz pixel clock, and a corresponding set register. When the counter reaches 0, an interrupt is generated. Intervals can range from 166.7µs to 11.9 minutes (?). The Sammy logo at the start of [[Viewpoint]] is an example of its use. [[Sengoku 3]] and [[Neo Turf Masters]] are also known to rely on them to do [[scanline effects]].
 == AES/MVS interrupts levels ==