Fix PLIC priority tie-breaking to favor lowest ID #635
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The RISC-V PLIC specification states that "if two or more pending interrupts have the same priority, the one with the lowest ID has the highest priority." The previous implementation used ilog2(), which identifies the most significant bit (highest ID). Replace it with rv_ctz() to select the least significant bit (lowest ID), ensuring compliance with the specification's arbitration rule.
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The RISC-V PLIC specification states that "if two or more pending interrupts have the same priority, the one with the lowest ID has the highest priority."
The previous implementation used ilog2(), which identifies the most significant bit (highest ID). Replace it with rv_ctz() to select the least significant bit (lowest ID), ensuring compliance with the specification's arbitration rule.
Summary by cubic
Fix PLIC tie-breaking to choose the lowest interrupt ID when multiple pending interrupts share the same priority, matching the RISC-V spec. Replaced ilog2() with rv_ctz() to select the least significant set bit in the pending-enabled mask.
Written for commit a7ca51b. Summary will update automatically on new commits.