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MB86R02 ‘Jade-D’ Hardware Manual V1.64
9.6.6 Notes on use of IRC
The notes on use of IRC is described.
Note concerning IRQ clear timing
When "0" is writed to the IRQF bit of the IRQF register as described in the explanation of "9.5.2 IRQ
flag register (IRQF)", IRQX to the ARM core (interrupt request) is negated. However, after "0" is
writed to IRQF, IRQX is actually negated during one cycle of the APB clock. Therefore, when the
code (interrupt handler) of which it is valid is the interrupt in the ARM core again immediately after "0"
was writed to IRQF is written, the ARM core has the possibility of entering the IRQ mode again by
mistake by IRQX before it is cleared. This has the possibility of occurring when the clock frequency in
the ARM core is especially faster than the frequency of IRC.
To evade this problem, add one dummy instruction (access instruction to the IRC interrupt register)
after IRQF clear instruction. As a result, guarantee for IRQX to be cleared surely before the interrupt
in the ARM core becomes valid again.
Summary of Contents for MB86R02
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Page 77: ...3 3 MB86R02 Jade D Hardware Manual V1 64 Figure 3 2 Memory map 2 ...
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Page 497: ...18 139 MB86R02 Jade D Hardware Manual V1 64 VSYNC is output 1 dot clock faster than HSYNC ...
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