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NAME
/harness/flash.bin
DESCRIPTION
Access the flash storage chip (where the harness firmware is
stored).
Reading from the file reads the raw flash contents.
Writing to the file does not accept raw data; instead the data
must be encapsulated in the [Intel Hex] format, with the Hex
file writing to the region 0x1000_0000-0x1010_0000. While less
convenient than verbatim data, the Hex format provides in-band
checksums and EOF-markers that help prevent rendering the
harness unbootable with corrupted or truncated writes. Any
holes in the Intel Hex file are filled with "1" bits. Once a
complete Intel Hex file has been written without error and the
file is closed, the harness reboots into the new firmware.
BUGS
- The size of the chip is configured at compile-time. If the
firmware is loaded onto hardware with a larger flash chip
than it was compiled for, then the upper part of the chip
will not be accessible with this file. If the firmware is
loaded onto hardware with a smaller flash chip than it was
compiled for, then accessing the missing upper part of the
chip will crash.
- When writing to the flash using this file, only half of the
chip capacity is usable (the size of the region specified
above is half the chip size); the top half and bottom half
are mirrors of each-other. This is to avoid the firmware
crashing as its program text is overwritten; the firmware is
executing out of the bottom half, and writing to the top
half; once the file is closed, a minimal in-RAM function
copies the top half to the bottom half and reboots.
SEE ALSO:
[Intel Hex]: https://archive.org/details/IntelHEXStandard
AUTHOR
Copyright (C) 2025 Luke T. Shumaker <lukeshu@lukeshu.com>
SPDX-License-Identifier: AGPL-3.0-or-later
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