53 lines
2.9 KiB
Markdown
53 lines
2.9 KiB
Markdown
This README describes the layout of system files and headers for
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microcontrollers supported by tinyusb from the vendor [ST](www.st.com).
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The CMSIS by ARM is an attempt to unify how system initialization and headers
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for ARM microcontrollers are handled across vendors. A vendor is expected to
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provide a number of files, including vendor-specific device headers,
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vendor-specific system init code (in C), vendor-specific startup code (coded in
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assembly _and_ meant to make writing C interrupt handlers easy), and ARM
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architecture-specific headers. In practice, it's actually difficult to find all
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these files in one place.
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* stm32cube generates a self-contained application. All the relevant headers,
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system init, and startup code are under `Drivers/CMSIS`. The linker script is
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stored at the root of your project, _along_ with a copy of the startup code.
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Relative to `Drivers/CMSIS`:
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* Device header files are stored under `Device/ST/$family/Include`.
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* Arm-provided CMSIS headers are stored under `Include`.
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* The portable C portion of the startup code, called `system_$family.c`, is
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stored under `Device/ST/$family/Source/Templates`. This "system init" code
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is required by CMSIS.
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* The assembly portion of the startup code, called `startup_$device.c`, is
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stored under `Device\ST\STM32F4xx\Source\Templates\gcc`.
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* Micropython maintains [a repo](https://github.com/micropython/stm32lib)
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with _only_ the device header files. We use that
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repo and provide the remaining files ourselves.
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* Micropython keeps the linker script and assembly portion of the startup
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code under the
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[boards](https://github.com/micropython/micropython/tree/master/ports/stm32/boards)
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directory in the stm32 port (but the code is board agnostic).
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* Micropython also embeds its own
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[copy](https://github.com/micropython/micropython/tree/master/lib/cmsis/inc)
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of CMSIS headers for all ARM targets into the repo.
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* Micropython indeed _does_ use their own custom C startup code (CMSIS system
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init) for
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[stm32](https://github.com/micropython/micropython/blob/master/ports/stm32/system_stm32.c)
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targets. It is
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[missing](https://github.com/micropython/micropython/commit/fdbc22e4d27b9d1c686647c9c67a32206f7bc83a)
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the `SystemCoreClockUpdate` function.
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* TinyUSB uses Micropython's [stm32lib](stm32lib) as a submodule to provide
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device headers. The remaining system files can be found in the following
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directories:
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* C system init code is in the [system-init](system-init) directory.
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* Assembly startup code is in the [startup](startup) directory. Each family
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gets its own subdirectory under startup (e.g. [stm32f4](startup/stm32f4)).
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* ARM-provided headers are stored in the [cmsis](cmsis) directory.
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* The linker script for the STM32F4-DISCOVERY board demo is supplied as
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part of TinyUSB's
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[Board Support Packages](../../bsp/stm32f407disco/STM32F407VGTx_FLASH.ld).
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The above files were extracted from a dummy stm32cube project in February
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2019.
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