Assertion Synthesis: Catching RTL Assertions on the FPGA
Golden Gate can synthesize assertions present in FIRRTL (implemented as
statements) that would otherwise be lost in the FPGA synthesis flow. Rocket
and BOOM include hundreds of such assertions which, when synthesized, can
provide great insight into why the target may be failing.
Enabling Assertion Synthesis
To enable assertion synthesis prepend
WithSynthAsserts config to your
PLATFORM_CONFIG. During compilation, Golden Gate will print the number of
assertions it’s synthesized. In the generated header, you will find the
definitions of all synthesized assertions. The
bridge driver will be automatically instantiated.
If an assertion is caught during simulation, the driver will print the assertion cause, the path to module instance in which it fired, a source locator, and the cycle on which the assertion fired. Simulation will then terminate.
An example of an assertion caught in a dual-core instance of BOOM is given below:
id: 1190, module: IssueSlot_4, path: FireSimNoNIC.tile_1.core.issue_units_0.slots_3]
at issue_slot.scala:214 assert (!slot_p1_poisoned)
at cycle: 2142042185
Just as in a software-hosted RTL simulation using verilator or VCS, the
reported cycle is the number of target cycles that have elapsed in the clock
domain in which the assertion was instantiated (in Chisel specifically this is
the implicit clock at the time you called
assert). If you rerun a FireSim
simulation with identical inputs, the same assertion should fire
deterministically at the same cycle.