st20-gp6 STMicroelectronics, st20-gp6 Datasheet - Page 33

• Manufacturer Part Number: st20-gp6
• Description: Gps Processor
• Manufacturer: STMicroelectronics

5.5
There are various restrictions that must be placed on interrupt handlers to ensure that they interact
correctly with the rest of the process model implemented in the CPU.
5.6
The interrupt controller is allocated a 4k block of memory in the internal peripheral address space.
Information on interrupts is stored in registers as detailed in the following section. The registers can
be examined and set by the devlw (device load word) and devsw (device store word) instructions.
Note, they can not be accessed using memory instructions.
HandlerWptr register
The HandlerWptr registers (1 per interrupt) contain a pointer to the workspace of the interrupt han-
dler. It also contains the Priority bit which determines whether the interrupt is at a higher or lower
priority than the high priority process queue.
Note, before the interrupt is enabled, by writing a 1 in the Mask register, the user (or toolset) must
ensure that there is a valid Wptr in the register.
HandlerWptr
Bit
1
0
31:2
1
2
3
4
Restrictions on interrupt handlers
Interrupt handlers must not deschedule.
Interrupt handlers must not execute communication instructions. However they may com-
municate with other processes through shared variables using the semaphore signal to
synchronize.
Interrupt handlers must not perform 2d block move instructions.
Interrupt handlers must not cause program traps. However they may be trapped by a
scheduler trap.
Interrupt configuration registers
Bit field
Priority
HandlerWptr
Table 5.1 HandlerWptr register format - one register per interrupt
Function
Sets the priority of the interrupt. If this bit is set to 0, the interrupt is a higher priority
than the high priority process queue, if this bit is 1, the interrupt is a lower priority
than the high priority process queue.
Pointer to the workspace of the interrupt handler.
Reserved, write 0.
Interrupt controller base address + #00 to #1C
0
1
high priority
low priority
Read/Write
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