Inter Edison平台CPU、MCU双核架构

Inter Edison包含双核：Host CPU、Slave MCU。框架如下



关于MCU使用详细信息参考Inter官方网站：
https://software.intel.com/zh-cn/node/557354#Waking_up_the_host_CPU_using_the_MCU
组成intel Edison 组成主要为两部分， Atom的核心 和 quark的MCU 

（不知道为何intel不说Quark，而只是称作MCU了，大家可以回帖揣测下） 

这是一个双CPU，双系统的模块，Atom核心运行着yocto版的linux，而quark的MCU部分则运行着Viper RTOS，这是风河提供了一套系统，包含了线程调度、内存管理、中断调度等等功能。

MCU应用运行在Viper内核上，并独立控制着连接MCU的外围设备，我们使用GPIO读写传感器就是由MCU完成的，然后MCU再和Atom处理器进行通信，传回数据，用以完成更多功能。MCU还可以用于省电，他能促使Atom核心休眠，等到需要的时候再唤醒。

MCU驱动提供了IPC协议支持，使得可以下载应用到我们的设备上。 
MCU子系统 

MCU子系统基于486架构，对奔腾IA ISA兼容，集成了 I/O (IPC, I2C, GPIO, HSU, DMA)和SRAM。其主要特性如下：
在fully active D0 device power状态，CPU频率是100MHz，在S0ix “active idle”休眠状态，CPU会降频到38.4 MHz。
SRAM: 192 KB SRAM（包括代码和数据）
IPC: 这个很重要，MCU提供了控制子系统的IPC机制，MCU和核心的thread-based通信也通过此进行。
I2C: I2C 8和I2C 9 in the system controller unit (SCU) cluster are assigned for MCU usage.
UART: MCU能访问UART1、UART2，which may be used as a Linux* kernel console as well.
GPIO: MCU能访问所有GPIO口，MCU和核心共用所有GPIO。
PWM: MCU和核心共用所有PWM
MCU 提供了微秒级 (1 µs)高精度延时API。详见： Auxiliary API 部分。
MCU提供了不同等级的追踪能力，用以调试程序。
The MCU SDK是一套基于Eclipse的SDK，方便用户创建、编译、下载和调试MCU应用，并且他支持多系统。

图片是SDK包含的东西： 




MCU应用 

MCU应用运行在Viper上，它的二进制文件存储在linux RootFS中，在linux内核启动期间，会通过MCU driver将二进制文件下载到MCU上。MCU应用能独立控制外设、和atom核心通信，也能进入低功耗模式。通过intel提供的SDK就可以开发MCU应用。

核心端接口 

以下列出了核心上暴露出的一些TTY通道和多个sysfs节点，这些接口都是用于核心和MCU间通信的。 
TTY接口
/dev/ttymcu0 : 核心与MCU的传输通道。核心和MCU间能通过这个接口相互发送和接受数据。
/dev/ttymcu1 : 用于获取MCU的log信息

Sysfs接口
/sys/devices/platform/intel_mcu/control : A write-only control node to load the MCU application. Currently this node is for internal use only.
/sys/devices/platform/intel_mcu/fw_version : The version of the MCU SDK that is used to build MCU applications.
/sys/devices/platform/intel_mcu/log_level : A read/write node to set and get the current MCU application log level. Supported input strings include fatal, error, warning, info, and debug.

MCU SDK 

MCU SDK主要是一个Eclipse plugin，它包含一个预建工具，能用于编译、下载和调试MCU应用。同时当创建项目时，会使用到其中包含的模板源码。MCU SDK主要有以下几个特性：
创建MCU项目
建立MCU应用
下载MCU应用到目标设备
显示调试信息

以下是一些intel官方提到的注意事项，主要为edison硬件的局限性说明，不做翻译了：
The maximum message size for interprocess communication between the CPU and the MCU is currently limited to 255 bytes.
The current Viper OS release does not support unloading an MCU user application after it is loaded. The user must reboot the device to unload the downloaded binary.
The MCU application update requires a Linux reboot.
Maximum MCU binary size is limited to 120 KB currently.
Due to the limitations of the current Viper OS release, the MCU OS tick value is 10 ms.
You cannot install the SDK in any directory that has spaces in the path name. (For example, Program Files or My Documents is not allowed.)
There is no floating point support in MCU. (You can build a floating point code using MCU, but it will generate runtime exceptions.)
The MCU is limited to 2xI2C.
The MCU application is limited to single-thread usage.
You cannot boot the MCU without first booting Linux.
There is no access coordination between the Intel Atom processor and the MCU. Both can configure the same I/O at once. This can potentially cause conflicts and must be user-managed.
The MCU SDK (Eclipse) is different and separate from the C/C++ Eclipse SDK for the Intel Atom processor.
The MCU I/O API is not aligned with the API for the Intel Atom processor. You must rewrite code to move from the Intel Atom processor to the MCU.
The MCU does not have a watchdog timer.
Currently, the SPI feature is not supported for the MCU.
It may take a long time to launch the MCU SDK on Windows under some network configurations due to Eclipse or Cygwin limitations.
Pin muxing (Arduino extension board configuration) must be done through the Linux interface before starting the MCU. For details, see Setting
the Intel® Edison board up to test system on a chip (SoC) GPIOs .
PWM runtime power management must be disabled from the Linux side in order to access this module. For details, see Controlling
PWM ports .
There are no programmable timer interrupts available on the MCU.