45 lines
1.8 KiB
Python
45 lines
1.8 KiB
Python
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"""Helpers for ESP32 flash images shared between the in-process bridge and
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the subprocess worker.
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The ESP-IDF compiler in `espidf_compiler.py` builds a full 4 MB merged flash
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image and then **trims the trailing 0xFF padding** before serializing the
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binary into the JSON compile response (issue #101 — sending the full 4 MB
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gave a ~5.5 MB base64 string that nginx / Cloudflare would buffer-fail with
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"No response from server"). The frontend stores the trimmed bytes; this
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module re-pads them on the receiving side just before QEMU attaches the
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image as an MTD drive — QEMU rejects flash sizes that aren't a power-of-2
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megabyte (2 / 4 / 8 / 16 MB).
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This is a lossless round trip: bytes after `last_used` in the compiler's
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merge are 0xFF by construction, so trim → pad reproduces the original
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image byte-for-byte.
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"""
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from __future__ import annotations
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# Sizes QEMU's esp32-picsimlab MTD layer accepts. ESP32 / S3 / C3 builds
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# all default to 4 MB (CONFIG_ESPTOOLPY_FLASHSIZE_4MB). We only ever
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# round UP — never down.
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_VALID_FLASH_SIZES = [s * 1024 * 1024 for s in (2, 4, 8, 16)]
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_MIN_FLASH_BYTES = 4 * 1024 * 1024
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def pad_to_flash_size(fw_bytes: bytes) -> bytes:
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"""Pad `fw_bytes` with 0xFF up to the next valid QEMU flash size.
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Returns the input unchanged when it's already at or above a valid size.
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Raises `ValueError` if the firmware exceeds the largest size we accept
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(16 MB) — at that point something is wrong with the upstream merge.
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"""
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target = next(
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(s for s in _VALID_FLASH_SIZES if s >= max(len(fw_bytes), _MIN_FLASH_BYTES)),
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None,
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)
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if target is None:
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raise ValueError(
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f'ESP32 firmware too large for QEMU: {len(fw_bytes)} bytes (max 16 MB)'
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)
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if len(fw_bytes) >= target:
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return fw_bytes
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return fw_bytes + b'\xff' * (target - len(fw_bytes))
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