firechip: add direct JTAG bridge - #2359
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Add a generic OpenOCD-compatible remote_bitbang JTAG server derived from
rocket-chip's src/main/resources/csrc/remote_bitbang.{cc,h} (originally from
the Berkeley/Spike riscv-isa-sim project; see LICENSE.Berkeley). accept() and
execute_command() are made non-blocking to fit the FireSim bridge tick model;
the server is otherwise protocol-only and target-agnostic.
Expose the target's JTAG DTM pins (TCK/TMS/TDI/TDO) to the host through a Golden Gate widget and host driver. The driver runs the shared remote_bitbang server so an external client such as OpenOCD can drive the target TAP. The bridge is opt-in via WithJTAGBridge and FireSimDirectJTAGRocketConfig; default configurations are unchanged. The stock Rocket JTAG TAP uses negedge-clocked logic, which Golden Gate's FAME-1 transform lowers to enable-gated posedge logic, so no rocket-chip changes are required.
Add a BridgeSuite test (JTAGModule) following the existing UART/BlockDev pattern. The DUT wires the bridge pins to a Rocket-Chip JTAG TAP whose only data register is IDCODE (0x00000001). The embedded remote_bitbang client resets the TAP, reads the IDCODE twice, and checks the value. The test picks a free TCP port at runtime and passes it via +jtag_rbb_port so parallel jobs do not collide on the default port.
jimfangx
self-requested a review
July 23, 2026 22:46
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Summary
Implementation
The bridge connects the target TCK, TMS, TDI, and TDO pins to a Golden Gate widget. The host driver consumes one remote-bitbang command per bridge tick and advances one target token for each pin update or TDO sample. A complete JTAG bit therefore uses multiple bridge operations.
The bridge is enabled by
WithJTAGBridgeand the provided direct-JTAG FireSim configuration. Default FireChip configurations remain unchanged.Testing
0x00000001IDCODE readsThe F1 test registration follows the existing upstream BridgeSuite pattern; functional metasim validation was run on the locally supported platform.