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The point of a writable execute-in-place file system is that a module can arrive after the firmware was built and still run without being copied into RAM. This demonstrates exactly that, end to end: it writes an NXFLAT module into xipfs the way a download would, declaring the size up front so the extent is exact, checks the file system can hand out a real flash pointer for it, and runs two instances concurrently. Both instances report the address of their own text and of their stack. The text address is the same in both and is inside the flash window -- it is the address the file occupies on the media -- while the stacks differ. While they run, the extent carries one pin per instance, which is what stops the defragmenter relocating code that is executing. Two subcommands cover the file system rather than the module. bench times a bulk read out of the mapped flash before and after a write, which on the RP2350 is the cost of whichever path the driver used to restore XIP. defrag fills the volume, deletes every other file until an allocation genuinely cannot be satisfied, compacts, retries the same allocation, then verifies every relocated file byte for byte and again after a remount, printing a block map at each step. The module has neither static data nor string constants, and reports through a callback into the firmware instead of formatting its own output. That is not stylistic: the ldnxflat in circulation resolves the GOT entries for .bss objects into the import table, and drops the addend when it resolves the PC-relative references to .rodata, so a module using either quietly computes wrong addresses. The comment in module/xipmod.c records both. The callback also exercises the other direction of the interface, firmware code entered with the module's data base still live in r10. Assisted-by: Claude Code:claude-opus-5 Signed-off-by: Marco Casaroli <marco.casaroli@gmail.com>
38 lines
1.2 KiB
Text
38 lines
1.2 KiB
Text
#
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# For a description of the syntax of this configuration file,
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# see the file kconfig-language.txt in the NuttX tools repository.
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#
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config EXAMPLES_NXFLATXIP
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tristate "NXFLAT execute-in-place from xipfs demo"
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depends on FS_XIPFS && NXFLAT && LIBC_EXECFUNCS
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default n
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---help---
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Write an NXFLAT module into xipfs at run time, the way a download
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would, then run two instances of it concurrently. The module's
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text is executed directly out of flash and shared between the
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instances, while each instance gets its own data.
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Subcommands:
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bench XIP read throughput before and after a flash write
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defrag fragment the volume, compact it, with a block map
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Building the module needs the mknxflat and ldnxflat host tools
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from the NuttX toolchain, and the board's Make.defs must name
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them, exactly as apps/examples/nxflat requires.
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if EXAMPLES_NXFLATXIP
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config EXAMPLES_NXFLATXIP_MOUNTPT
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string "xipfs mountpoint"
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default "/mnt/xipfs"
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config EXAMPLES_NXFLATXIP_MTD
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string "MTD device backing the volume"
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default "/dev/rpflash"
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---help---
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Used only by the defrag subcommand, which remounts the volume to
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show that what it did survives.
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endif # EXAMPLES_NXFLATXIP
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