68k interrupts: Difference between revisions

Revision as of 17:42, 2 December 2012

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 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 2 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 after cold reset: Level 2

CD interrupts levels

VBlank: Level 1
Timer: Level 0

@@ Line 23: / Line 23: @@
 == [[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]].
+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 2]] and [[Neo Turf Masters]] are also known to rely on them to do [[scanline effects]].
 == AES/MVS interrupts levels ==