OS-9 for the Prospector P1100 Board Guide
OS-9 for the Prospector P1100 Board Guide
OS-9 for the Prospector P1100 Board Guide
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Note<br />
Fast Interrupt Vector (0x7)<br />
The ARM4 defined fast interrupt (FIQ) mapped to vector 0x7 is handled<br />
differently by <strong>the</strong> <strong>OS</strong>-9 interrupt code and can not be used as freely as<br />
<strong>the</strong> external interrupt mapped to vector 0x6. To make fast interrupts as<br />
quick as possible <strong>for</strong> extremely time critical code, no context in<strong>for</strong>mation<br />
is saved on exception and FIQs are never masked. This requires any<br />
exception handler to save and restore its necessary context if <strong>the</strong> FIQ<br />
mechanism is to be used. This requirement means that a FIQ handler’s<br />
entry and exit points must be in assembly, as <strong>the</strong> C compiler will make<br />
assumptions about context. In addition, no system calls are possible<br />
unless a full C ABI context save has been done first. The <strong>OS</strong>-9 IRQ<br />
code <strong>for</strong> <strong>the</strong> SA11X0 has assigned all interrupts as normal external<br />
interrupts and <strong>the</strong> user must re-define a source as an FIQ to make use<br />
of this feature.<br />
44 <strong>OS</strong>-9 <strong>for</strong> <strong>the</strong> <strong>Prospector</strong> <strong>P1100</strong> <strong>Board</strong> <strong>Guide</strong>
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