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INTERRUPT CONTROLLER S3C2440A RISC MICROPROCESSOR
14-6
INTERRUPT PRIORITY
Each arbiter can handle six interrupt requests based on the one bit arbiter mode control (ARB_MODE) and two
bits of selection control signals (ARB_SEL) as follows:
If ARB_SEL bits are 00b, the priority order is REQ0, REQ1, REQ2, REQ3, REQ4, and REQ5.
If ARB_SEL bits are 01b, the priority order is REQ0, REQ2, REQ3, REQ4, REQ1, and REQ5.
If ARB_SEL bits are 10b, the priority order is REQ0, REQ3, REQ4, REQ1, REQ2, and REQ5.
If ARB_SEL bits are 11b, the priority order is REQ0, REQ4, REQ1, REQ2, REQ3, and REQ5.
Note that REQ0 of an arbiter always has the highest priority, and REQ5 has the lowest one. In addition, by
changing the ARB_SEL bits, we can rotate the priority of REQ1 to REQ4.
Here, if ARB_MODE bit is set to 0, ARB_SEL bits doesn’t change automatically changed, making the arbiter to
operate in the fixed priority mode (note that even in this mode, we can reconfigure the priority by manually
changing the ARB_SEL bits). On the other hand, if ARB_MODE bit is 1, ARB_SEL bits are changed in rotation
fashion, e.g., if REQ1 is serviced, ARB_SEL bits are changed to 01b automatically so as to put REQ1 into the
lowest priority. The detailed rules of ARB_SEL change are as follows:
If REQ0 or REQ5 is serviced, ARB_SEL bits are not changed at all.
If REQ1 is serviced, ARB_SEL bits are changed to 01b.
If REQ2 is serviced, ARB_SEL bits are changed to 10b.
If REQ3 is serviced, ARB_SEL bits are changed to 11b.
If REQ4 is serviced, ARB_SEL bits are changed to 00b.