st20-gp6 STMicroelectronics, st20-gp6 Datasheet - Page 25

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

There are four groups of traps, as detailed below.
Trap groups encoding is shown in Table 4.3 below. These codes are used to identify trap groups to
various instructions.
trap handler
•
•
•
•
Breakpoint
Breakpoint
This group consists of the Breakpoint trap. The breakpoint instruction ( j0 ) calls the break-
point routine via the trap mechanism.
Errors
The traps in this group are IntegerError and Overflow . Overflow represents arithmetic over-
flow, such as arithmetic results which do not fit in the result word. IntegerError represents
errors caused when data is erroneous, for example when a range checking instruction finds
that data is out of range.
System operations
This group consists of the LoadTrap , StoreTrap and IllegalOpcode traps. The IllegalOpcode
trap is signalled when an attempt is made to execute an illegal instruction. The LoadTrap
and StoreTrap traps allow a kernel to intercept attempts by a monitored process to change
or examine trap handlers or trapped process information. It enables a user program to sig-
nal to a kernel that it wishes to install a new trap handler.
Scheduler
The scheduler trap group consists of the ExternalChannel, InternalChannel, Timer,
TimeSlice, Run, Signal, ProcessInterrupt and QueueEmpty traps. The ProcessInterrupt
trap signals that the machine has performed a priority interrupt from low to high. The
QueueEmpty trap indicates that there is no further executable work to perform. The other
traps in this group indicate that the hardware scheduler wants to schedule a process on a
process queue, with the different traps enabling the different sources of this to be moni-
tored.
The scheduler traps enable a software scheduler kernel to use the hardware scheduler to
implement a multi-priority software scheduler.
Note that scheduler traps are different from other traps as they are caused by the micro-
scheduler rather than by an executing process.
trap handler
CPU Error
Low priority traps
System operations
trap handler
Figure 4.4 Trap arrangement
trap handler
Scheduler
trap handler
Breakpoint
trap handler
CPU Error
High priority traps
System operations
trap handler
trap handler
Scheduler
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