st20-gp1 STMicroelectronics, st20-gp1 Datasheet - Page 25

• Manufacturer Part Number: st20-gp1
• Description: Gps Processor
• Manufacturer: STMicroelectronics

Trap groups encoding is shown in Table 4.4 below. These codes are used to identify trap groups to
various instructions.
In addition to the trap groups mentioned above, the CauseError flag in the Status register is used
to signal when a trap condition has been activated by the causeerror instruction. It can be used to
indicate when trap conditions have occurred due to the user setting them, rather than by the
system.
4.6.2
Table 4.4 summarizes the events that can cause traps and gives the encoding of bits in the trap
Status and Enable words.
Trap cause
Breakpoint
IntegerError
Overflow
IllegalOpcode
LoadTrap
StoreTrap
InternalChannel
ExternalChannel
Timer
Timeslice
Run
Signal
ProcessInterrupt
QueueEmpty
CauseError
Events that can cause traps
15 (Status only)
Status/Enable
codes
10
11
12
13
0
1
2
3
4
5
6
7
8
9
Table 4.4 Trap causes and Status/Enable codes
encoded
group
Trap
Any,
Trap group
Breakpoint
CPU Errors
System operations
Scheduler
0-3
0
1
1
2
2
2
3
3
3
3
3
3
3
3
Table 4.3 Trap group codes
Comments
When a process executes the breakpoint instruction ( j0 ) then it traps
to its trap handler.
Integer error other than integer overflow – e.g. explicitly checked or
explicitly set error.
Integer overflow or integer division by zero.
Attempt to execute an illegal instruction. This is signalled when opr
(operate) is executed with an invalid operand.
When the trap descriptor is read with the ldtraph (load trap handler)
instruction or when the trapped process status is read with the
ldtrapped (load trapped) instruction.
When the trap descriptor is written with the sttraph (store trap handler)
instruction or when the trapped process status is written with the
sttrapped (store trapped) instruction.
Scheduler trap from internal channel.
Scheduler trap from external channel.
Scheduler trap from timer alarm.
Scheduler trap from timeslice.
Scheduler trap from runp (run process) or startp (start process).
Scheduler trap from signal .
Start executing a process at a new priority level.
Caused by no process active at a priority level.
Signals that the causeerror instruction set the trap flag.
Code
0
1
2
3
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