mirror of
https://github.com/ratspeak/C6-Reticulum-ASM
synced 2026-08-12 18:07:18 -04:00
194de5656d
Polled NS16550A TX: spin on LSR.THRE (offset 5, bit 5 = 0x20), then write a0 to THR (offset 0). Leaf, no spill, single ret. Pulls UART0_BASE / UART0_LSR_THRE from src/include/regs.S so the qemu-virt and (future) C6 builds share the same source. Static checks confirm: lui t0, 0x10000 (UART0_BASE), lbu/andi/beqz poll loop, sb a0,0(t0), and ABI compliance (no s* writes, a0 not clobbered).
62 lines
2.4 KiB
Python
62 lines
2.4 KiB
Python
"""Tests for src/uart/uart_tx_byte.S.
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Static disassembly checks: the body matches the NS16550A polled-TX shape
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(load UART0_BASE → spin on LSR.THRE → store a0 to THR → ret). The
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integration test (firmware emits a known byte, EmuTarget reads it from
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qemu's serial) lands once _main is wired.
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"""
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from __future__ import annotations
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import re
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import pytest
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from harness import build
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@pytest.fixture(scope="module")
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def artifacts() -> build.BuildArtifacts:
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return build.build("qemu-virt")
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def test_function_exists(artifacts: build.BuildArtifacts) -> None:
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assert build.symbol_address(artifacts.elf, "uart_tx_byte") > 0
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def test_loads_uart0_base(artifacts: build.BuildArtifacts) -> None:
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body = build.objdump_disassemble(artifacts.elf, symbol="uart_tx_byte")
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# `li t0, UART0_BASE` (0x10000000) → assembler emits `lui t0, 0x10000`
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# since the base has zero low 12 bits.
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assert re.search(r"\blui\b\s+t0,\s*0x10000\b", body), body
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def test_polls_lsr_and_masks_thre(artifacts: build.BuildArtifacts) -> None:
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body = build.objdump_disassemble(artifacts.elf, symbol="uart_tx_byte")
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# Read LSR at offset 5, AND with 0x20 (THRE), branch back if zero.
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assert re.search(r"\blbu\b\s+t1,\s*5\(t0\)", body), body
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assert re.search(r"\bandi\b\s+t1,\s*t1,\s*32\b", body), body
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assert re.search(r"\bbeqz\b\s+t1", body), body
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def test_writes_byte_to_thr(artifacts: build.BuildArtifacts) -> None:
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body = build.objdump_disassemble(artifacts.elf, symbol="uart_tx_byte")
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# Store argument byte (a0) to THR (offset 0 from base).
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assert re.search(r"\bsb\b\s+a0,\s*0\(t0\)", body), body
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def test_returns(artifacts: build.BuildArtifacts) -> None:
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body = build.objdump_disassemble(artifacts.elf, symbol="uart_tx_byte")
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assert "ret" in body or "jalr\tzero" in body
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def test_does_not_touch_callee_saved_or_a0(artifacts: build.BuildArtifacts) -> None:
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"""ABI: a0 carries the input and is not modified; s0..s11 are not touched."""
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body = build.objdump_disassemble(artifacts.elf, symbol="uart_tx_byte")
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for match in re.findall(r"\b(s\d+)\b,", body):
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pytest.fail(f"uart_tx_byte writes callee-saved {match}: {body}")
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# a0 only appears as the source of the sb (read), never as a destination.
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for line in body.splitlines():
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m = re.search(r"^\s*[0-9a-f]{8}:\s+\S+\s+(\w+)\s+(a0)\b", line)
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if m and m.group(1) not in {"sb", "sh", "sw"}:
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pytest.fail(f"uart_tx_byte writes a0: {line}")
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