TMS320C6727B, TMS320C6726B, TMS320C6722B, TMS320C6720

Floating-Point Digital Signal Processors

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SPRS370C–SEPTEMBER 2006–REVISED OCTOBER 2007

4.10 External Interrupts

The C672x DSP has no dedicated general-purpose interrupt pins, but the dMAX can be used in combination with a McASP AMUTEIN signal to provide external interrupt capability. There is a multiplexer for each McASP, controlled by the CFGMCASP0/1/2 registers, which allows the AMUTEIN input for that McASP to be sourced from one of seven I/O pins on the DSP. Once a pin is configured as an AMUTEIN source, a very short pulse (two SYSCLK2 cycles or more) on that pin will generate an event to the dMAX. This event can trigger the dMAX to generate a CPU interrupt by programming the assoicated Event Entry.

There are a few additional points to consider when using the AMUTEIN signal to enable external interrupts as described above. The I/O pin selected by the CFGMCASP0/1/2 registers must be configured as a general-purpose input pin within the associated peripheral. Also, the AMUTEIN signal should be disabled within the corresponding McASP so that AMUTE is not driven when AMUTEIN is active. This can be done by clearing the INEN bit of the AMUTE register inside the McASP. Finally, AMUTEIN events are logically ORed with the McASP transmit and receive error events within the dMAX; therefore, the ISR that processes the dMAX interrupt generated by these events must discern the source of the event.

The EMIF EM_WAIT pin has the ability to generate an NMI (INT1) based upon a rising edge on the EM_WAIT pin. Note that while this interrupt is connected to the CPU NMI (non-maskable interrupt), it is actually maskable through the EMIF control registers. In fact, the default state for this interrupt is disabled. Also, interrupt generation always occurs on a rising edge of EM_WAIT; the polarity selection for wait state generation has no effect on the interrupt polarity. The EM_WAIT pin should remain asserted for at least two SYSCLK3 cycles to ensure that the edge is detected.