Interrupts
Tue, 09/30/2008 - 11:39 — mpare
Real Time Interrupt (RTI)
The RTI can be used to generate a hardware interrupt at a fixed periodic rate. If enabled (by setting RTIE=1), this interrupt will occur at the rate selected by the RTICTL register. The RTI timer runs with OSCCLK. See Figure 40. The RTIF bit is set to one at the end of the RTI time-out period.
When coming out of reset, all the interrupts are disabled. This is done because the interrupts use the stack, so we have to set up the stack first before we should initialize the stack. We don't know when in a routine that a RTI will call the interrupt subroutine so we must have a functioning stack or else all hell will break loose.
$$RTI \; Timeout = \frac{Clock \; Speed}{1024 \cdot 2^{RTR[6:4]-1}} \bmod RTR[3:0]$$
Interrupt Mask
This essentially tells the processor that you are doing something important and don't want to be interrupted. Just by setting the IRQ interrupt mask high in the CCR (Condition Control Register) will place a "Do not distrub" sign. But ocassionally there will be something so important, maybe an emergency, that can bypass the IRQ Interrupt mask, it is the XIRG Interrupt formally known as the non-maskable interrupt. Once you turn XIRQ on (high) you can't turn it off again my software, it will require a hardware reset or something.
Example Program Using RTI
| Attachment | Size |
|---|---|
| RTI Rates.xls | 143 KB |
Comments
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