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Hardware Interrupts

Thread Scheduling 4-11

4.2 Hardware Interrupts

Hardware interrupts handle critical processing that the application must

perform in response to external asynchronous events. The DSP/BIOS HWI

module is used to manage hardware interrupts.

In a typical DSP system, hardware interrupts are triggered either by on-

device peripherals or by devices external to the DSP. In both cases, the

interrupt causes the processor to vector to the ISR address. The address to

which a DSP/BIOS HWI object causes an interrupt to vector can be a user

routine or the common system HWI dispatcher.

Hardware ISRs can be written using assembly language, C, or a combination

of both. HWI functions are usually written in assembly language for efficiency.

To allow an HWI object’s function to be written completely in C, the system

HWI dispatcher should be used.

All hardware interrupts run to completion. If an HWI is posted multiple times

before its ISR has a chance to run, the ISR runs only one time. For this

reason, you should minimize the amount of code performed by an HWI

function. If the GIE bit is enabled, a hardware interrupt can be preempted by

any interrupt that is enabled by the IEMASK.

If an HWI function calls any of the PIP APIs—PIP_alloc, PIP_free, PIP_get,

PIP_put—the pipe's notifyWriter or notifyReader functions run as part of the

HWI context.

Note:

The interrupt keyword or INTERRUPT pragma must not be used when

HWI objects are used in conjunction with C functions. The

HWI_enter/HWI_exit macros and the HWI dispatcher contain this

functionality, and the use of the C modifier can cause catastrophic results.

4.2.1 Configuring Interrupts with the Configuration Tool

In the DSP/BIOS configuration template, the HWI Manager contains an HWI

object for each hardware interrupt in your DSP.

Using the HWI Manager in the Configuration Tool, you can configure the ISR

for each hardware interrupt in the DSP.

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Coma FW-C2800 User's Guide Page 116