TC1796
System Units (Vol. 1 of 2)
Interrupt System
User’s Manual
14-22
V2.0, 2007-07
Interrupt, V2.0
14.8.6
Interrupt Priority 1
Interrupt Priority 1 is the first and lowest-priority entry in the Interrupt Vector Table. It is
generally reserved for ISRs which perform task management. ISRs whose actions cause
software-managed tasks to be created post a software interrupt request at priority level 1
to signal the event.
The ISR that triggers this event can then execute a normal return from interrupt. There
is no need for it to check whether the ISR is returning to the background-task priority level
(priority 0) or is returning to a lower-priority ISR that it interrupted. When there is a
pending interrupt at a priority higher than the return context for the current interrupt, this
interrupt will then be serviced. When a return to the background-task priority level
(level 0) is performed, the software-posted interrupt at priority level 1 will be serviced
automatically.
14.8.7
Software-Initiated Interrupts
Software can set the service request bit (SRR) in a SRN by writing to its Service Request
Control Register. Thus, software can initiate interrupts that are handled by the same
mechanism as hardware interrupts.
After the SRR bit is set in an active SRN, there is no way to distinguish between a
software-initiated interrupt request and a hardware interrupt request. For this reason,
software should only use SRNs and interrupt priority numbers that are not being used for
hardware interrupts.
The TC1796 contains four SRNs that support software-initiated interrupts. These SRNs
are not connected to peripheral modules and can only cause interrupts when software
sets its SRR bit. These SRNs are called the CPU Service Request Nodes
(CPU_SRC[3:0]). The PCP can also cause these four SRNs to generate service
requests. See also
for TC1796-specific implementation details of the four
CPU Service Request Control Registers.
Additionally, any otherwise unused SRN can be employed to generate software
interrupts.
14.8.8
External Interrupts
Two SRNs, DMA_SYSSRC2 and DMA_SYSSRC3, are reserved to handle external
interrupts. The setup for external GPIO port input signals (edge/level triggering, gating
etc.) that are able to generate an interrupt request is controlled in the External Request
Unit (ERU). The ERU functionality is described in detail in
.