ST20-GP1 View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

ST20-GP1

GPS PROCESSOR

STMicroelectronics 

ST20-GP1

Trap groups encoding is shown in Table 4.4 below. These codes are used to identify trap groups to

various instructions.

Trap group

Breakpoint

CPU Errors

System operations

Scheduler

Code

0

1

2

3

Table 4.3 Trap group codes

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 Events that can cause traps

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

Status/Enable Trap Comments

codes

group

Breakpoint

0

0

When a process executes the breakpoint instruction (j0) then it traps

to its trap handler.

IntegerError

1

1

Integer error other than integer overflow – e.g. explicitly checked or

explicitly set error.

Overflow

2

1

Integer overflow or integer division by zero.

IllegalOpcode

3

2

Attempt to execute an illegal instruction. This is signalled when opr

(operate) is executed with an invalid operand.

LoadTrap

4

2

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.

StoreTrap

5

2

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.

InternalChannel

6

3

Scheduler trap from internal channel.

ExternalChannel

7

3

Scheduler trap from external channel.

Timer

8

3

Scheduler trap from timer alarm.

Timeslice

9

3

Scheduler trap from timeslice.

Run

10

3

Scheduler trap from runp (run process) or startp (start process).

Signal

11

3

Scheduler trap from signal.

ProcessInterrupt

12

3

Start executing a process at a new priority level.

QueueEmpty

13

3

Caused by no process active at a priority level.

CauseError

15 (Status only) Any, Signals that the causeerror instruction set the trap flag.

encoded

0-3

Table 4.4 Trap causes and Status/Enable codes

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