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XC161-32 Derivatives
System Units (Vol. 1 of 2)
Interrupt and Trap Functions
Field
Bits
Type
Description
GLVL
[1:0]
rw
Group Priority Level
(Is completed by bit GPX to the 3-bit group level)
Highest priority level
3H
…
…
0H
Lowest priority level
1) Bit xxIR supports bit-protection.
When accessing interrupt control registers through instructions which operate on word
data types, their upper 7 bits (15 … 9) will return zeros when read, and will discard
written data. It is recommended to always write zeros to these bit positions. The layout
of the interrupt control registers shown below applies to each xxIC register, where “xx”
represents the mnemonic for the respective source.
The Interrupt Request Flag is set by hardware whenever a service request from its
respective source occurs. It is cleared automatically upon entry into the interrupt service
routine or upon a PEC service. In the case of PEC service, the Interrupt Request flag
remains set if the COUNT field in register PECCx of the selected PEC channel
decrements to zero and bit EOPINT is cleared. This allows a normal CPU interrupt to
respond to a completed PEC block transfer on the same priority level.
Note: Modifying the Interrupt Request flag via software causes the same effects as if it
had been set or cleared by hardware.
The Interrupt Enable Control Bit determines whether the respective interrupt node
takes part in the arbitration process (enabled) or not (disabled). The associated request
flag will be set upon a source request in any case. The occurrence of an interrupt request
can so be polled via xxIR even while the node is disabled.
Note: In this case the interrupt request flag xxIR is not cleared automatically but must be
cleared via software.
Interrupt Priority Level and Group Level
The four bits of bitfield ILVL specify the priority level of a service request for the
arbitration of simultaneous requests. The priority increases with the numerical value of
ILVL: so, 0000B is the lowest and 1111B is the highest priority level.
When more than one interrupt request on a specific level becomes active at the same
time, the values in the respective bitfields GPX and GLVL are used for second level
arbitration to select one request to be serviced. Again, the group priority increases with
the numerical value of the concatenation of bitfields GPX and GLVL, so 000B is the
lowest and 111B is the highest group priority.
Note: All interrupt request sources enabled and programmed to the same priority level
must always be programmed to different group priorities. Otherwise, an incorrect
interrupt vector will be generated.
User’s Manual
ICU_X1, V2.2
5-7
V1.0, 2004-02