Program 10: Environment-call trap

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Purpose

Execute a legal ECALL and verify terminal environment-call handling without executing the following instruction.

This is a negative test: the named trap is the expected outcome, not a failed simulation.

Setup

Property	Value
Benchmark workload ID	program-10
Headless selection	--program 10
Visualizer scenario	rv32i-program10
Registered test	RV32ISingleCycleSystemTest/program-10
Instruction image	3 words, starting at 0x00000000; last word at 0x00000008
Initial state	PC = 0x00000000; all registers zero; neither halted nor trapped
Memories	Separate instruction and data memories, 256 KiB each; unlisted data bytes zero

Start address	Bytes, in increasing address order
None	—

The table lists the complete preloaded data image, not instruction bytes. No data image is required.

Register	Role established by the program
x1	Value written before ECALL
x2	Must remain zero after ECALL

The shared setup describes reset, loading, and the behavioral-core selection. These hand-written programs do not use the standard ABI stack.

Assembly

Every instruction word is shown, including words that a trap or branch may prevent from executing. Address and word comments identify the exact fixture image.

addi x1, x0, 1                 # 0x00000000 | 0x00100093
ecall                          # 0x00000004 | 0x00000073
addi x2, x0, 2                 # 0x00000008 | 0x00200113

Execution

1. ADDI at 0x00 writes x1=1.
2. ECALL at 0x04 is legally decoded but requests an environment call. The reference sets EnvironmentCall and leaves PC at 0x04.
3. The ADDI at 0x08 never executes, so x2 remains zero. There are two attempts and no stores.

Unlike Program 9, this is not an illegal encoding. This environment does not provide a syscall service or a resumable handler; ECALL is a terminal trap.

Expected result

These are the fixture's explicit final-state assertions. Unlisted registers are not implicitly zero; their values follow the assembly. The store table enumerates every written byte, including zero-valued writes.

Item	Expected value	Meaning
x1	0x00000001	Value written before ECALL
x2	0x00000000	Must remain zero after ECALL
PC	0x00000004	Faulting attempt address
Attempts	2	Checkpoints I0–I1
HALTED	0	No EBREAK halt
TRAPPED	1	Expected terminal exception
TRAP_CAUSE	2	EnvironmentCall, a project enum code

Start address	Bytes, in increasing address order
None	—

No data writes occur; the initial data image is unchanged. HALTED remains 0 and TRAPPED becomes 1; ECALL is not the project's EBREAK halt.

Simulation and checkpoints

For a headless functional check, run build/rv32i_experiment --core single --program 10 --period 4000 --max-cycles 4096 --allocation-limit-mib 512. Select baseline or advanced for the same fixture on another core; add --fidelity reference for the structural-datapath reference profile. The explicit period is a scheduling choice, not a performance result. Use the campaign procedure for clock-certified measurements.

All 2 instruction attempts are included, with absolute simulator time and checkpoint number. The terminal fault is included. The table is scrollable in both directions. Observation conventions distinguish these attempts from loaded word addresses and hardware cycles.

All 2 instruction-attempt checkpoints of RV32ISingleCycleSystemTest/program-10, with a behavioral core. Times are absolute simulator units, not milliseconds or an ISA latency.

Checkpoint	Time	Instruction / address	Expected architectural effects
I0	7080	ADDI @ 0x00000000	raw=0x00100093, pc_after=0x00000004, wb=x1=0x00000001, mem=None, flow=next
I1	11080	ECALL @ 0x00000004	raw=0x00000073, pc_after=0x00000004, wb=None, mem=None, flow=next, trapped=true cause=EnvironmentCall

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