# PX4 参考飞行控制器设计
第1-3代 FMU 设计用于开源硬件，但到了第4-5代只提供 pin 输出引脚和供电规格（原理图由个人开发者生成）。 为了可以更好的确保兼容性，FMUv6 及更新的版本重新提供完整的设计模型。
- FMUv1：开发板 \（STM32F407, 128 KB RAM, 1MB flash, 原理图 (opens new window)\）（PX4 不再支持）
- FMUv2：Pixhawk \（STM32F427, 168 MHz, 192 KB RAM, 1MB flash, 原理图 (opens new window)\）
- FMUv3：2MB Flash 的 Pixhawk 变种 \（3DR Pixhawk 2 \（Solo\）， Hex Pixhawk 2.1，Holybro Pixfalcon，3DR Pixhawk Mini，STM32F427，168 MHz，256 KB RAM，2 MB flash，原理图 (opens new window)\）
- FMUv4：Pixracer \（STM32F427, 168 MHz, 256 KB RAM, 2MB flash, 原理图 (opens new window)\）
- FMUv4 PRO: Drotek Pixhawk 3 PRO (STM32F469, 180 MHz, 384 KB RAM, 2 MB flash, 输出引脚 (opens new window))
- FMUv5: Holybro Pixhawk 4 (STM32F765, 216 MHz, 512 KB RAM, 2 MB flash, 输出引脚 (opens new window))
- FMUv6：尚未完成，最终命名为 TBD，变种 6s (STM32H7, 400 MHz, 2 MB RAM, 2 MB flash) 和变种 6i (i.MX RT1050, 600 MHz, 512 KB RAM, 外部 flash)
# Main/IO Function Breakdown
The diagram below shows the division of bus and functional responsibilities between the FMU and I/O boards in a Pixhawk-series flight controller (the boards are incorporated into a single physical module).
Some Pixhawk-series controllers are built without the I/O board in order to reduce space or complexity, or to better address certain board use-cases.
The I/O board is disabled by setting parameter SYS_USE_IO=0. When the I/O board is disabled:
- The MAIN mixer file is loaded into the FMU (so the "MAIN" outputs listed in the Airframe Reference appear on the port labeled AUX). The AUX mixer file isn't loaded, so outputs defined in this file are not used.
- RC input goes directly to the FMU rather than via the IO board.
Flight controllers without an I/O board have
MAIN ports, but they do not have
AUX ports. Consequently they can only be used in airframes that do not use
AUX ports, or that only use them for non-essential purposes (e.g. RC passthrough). They can be used for most multicopters and fully autonomous vehicles (without a safety pilot using RC control), as these typically only use
MAIN ports for motors/essential controls.
Flight controllers without an I/O board cannot be used in airframes that map any
AUX ports to essential flight controls or motors (as they have no
Manufacturer flight controller variants without an I/O board are often named as a "diminutive" of a version that includes the I/O board: e.g. Pixhawk 4 Mini_, CUAV v5 nano.
Most PX4 PWM outputs are mapped to either
AUX ports in mixers. A few specific cases, including camera triggering and Dshot ESCs, are directly mapped to the FMU pins (i.e. they will output to either
AUX, depending on whether or not the flight controller has an I/O board).