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[rv_dm] Fix dmcontrol read to return 0 for haltreq and resumereq - #31209
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Fixes lowRISC#23204. According to the RISC-V Debug Specification (v0.13.2), the dmcontrol.haltreq and dmcontrol.resumereq fields are defined as write-only, and should always return 0 when read. This PR introduces a dmcontrol_read intermediary that explicitly zeroes out these write-only fields before returning the register data to the debugger via the DMI response queue.
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Closing this PR since the OpenTitan CI strictly blocks direct modifications to the vendored |
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Fixes #23204.
According to the RISC-V Debug Specification (v0.13.2, Section 3.12.2), the
dmcontrol.haltreqanddmcontrol.resumereqfields are defined as write-only, and should always return 0 when read. However, the current implementation returns the latcheddmcontrol_qdirectly, allowing a debugger to read these bits back as 1.This PR introduces a
dmcontrol_readintermediary that explicitly zeroes out these write-only fields before returning the register data to the DMI response queue. This brings the RTL into compliance with the spec.This is technically an upstream change for
pulp-platform/riscv-dbgbut they actually already implemented this exact fix in their master branch. This PR ports the same fix logic back to the vendored OpenTitan copy.