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Diffstat (limited to 'docs/reference/mpyfiles.rst')
| -rw-r--r-- | docs/reference/mpyfiles.rst | 15 |
1 files changed, 13 insertions, 2 deletions
diff --git a/docs/reference/mpyfiles.rst b/docs/reference/mpyfiles.rst index b2d552d09..9687f5e46 100644 --- a/docs/reference/mpyfiles.rst +++ b/docs/reference/mpyfiles.rst @@ -179,8 +179,19 @@ If bit #6 of the header's feature flags byte is set, then a vuint containing optional architecture-specific information will follow the header. The contents of this integer depends on which native architecture the file is meant for. -See also ``mpy-tool.py``'s ``-march-flags`` command-line option to set this -value when creating MPY files. +This is currently used to store which RISC-V processor extensions the MPY file +needs to operate correctly besides I, M, C, and Zicsr. Different flavours of +ArmV7 are identified by their native architecture number, but reusing that +mechanism would complicate things for RV32 and RV64. + +MPY files targeting RV32 or RV64 that do not need any particular processor +extensions do not need to provide a flags integer (along with setting the +appropriate bit in the header). The lack of a flags value for RV32 and RV64 +MPY files is used to indicate that no specific extensions are needed, and saves +one byte in the final output binary. + +See also the ``-march-flags`` command-line option in both ``mpy-tool.py`` and +``mpy-cross`` to set this value when creating MPY files. The global qstr and constant tables ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |