amiga kernel: restore INTENA's master bit when leaving a Paula interrupt - #158
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A program may hold a Disable() and still turn the hardware interrupts back on itself (Speedway Manager cracktro: Disable(), INTENA=$C020, AddIntServer(VERTB), spin on the server's counter). Our VERTB servers take Disable()/Enable() sections (timer.device's vblank handler, the graphics VBlank server), and with the interrupted task's IDNestCnt at 0 their Enable() never writes $C000 again, so the first vertical blank silently cleared INTEN and the program froze (issue #742). Kickstart's Enable() behaves the same, but its VERTB servers never do this. Interrupt handling must be transparent to the interrupted code: the master bit was set or the interrupt could not have happened, so set it again on the way out of the level 1-6 handlers.
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This fixed all the demos having issues for OCS and AGA that come with ApolloOS. |
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A program may hold a Disable() and still turn the hardware interrupts back on itself (Speedway Manager cracktro: Disable(), INTENA=$C020, AddIntServer(VERTB), spin on the server's counter). Our VERTB servers take Disable()/Enable() sections (timer.device's vblank handler, the graphics VBlank server), and with the interrupted task's IDNestCnt at 0 their Enable() never writes $C000 again, so the first vertical blank silently cleared INTEN and the program froze (issue #742). Kickstart's Enable() behaves the same, but its VERTB servers never do this.
Interrupt handling must be transparent to the interrupted code: the master bit was set or the interrupt could not have happened, so set it again on the way out of the level 1-6 handlers.