1、CM3計算板簡介

把樹莓派搬到自己的產品中，一種和樹莓派基礎功能一模一樣的板卡，并對相關管腳擴展，完成產品級的功能設計和硬件設計。板卡如下圖所示，運行的是Linux操作系統。

2、下載鏡像

CM3有多種內存搭配，常見的SD卡+EMMC板載存儲設備。運行的Linux鏡像應該不超過CM3的存儲容量，并預留一定的空間，我這塊CM3是常規的4GB EMMC，因此下載鏡像選擇為Lite版本。

下載鏡像地址：https://www.raspberrypi.org/downloads/raspbian/

選擇最新的Raspbian Buster Lite。

3、燒寫鏡像

網上購買一個CM3底板，用于燒寫鏡像。例如，微雪的底板：

燒錄鏡像步驟：

3.1、把CM3識別成存儲設備

3.1.1 CM3 boot方式配置

The 4GB eMMC Flash device on CM3 is directly connected to the primary BCM2837 SD/eMMC interface. These connections are not accessible on the module pins. On CM3L this SD interface is available on the SDX pins. When initially powered on, or after the RUN pin has been held low and then released, the BCM2837 will try to access the primary SD/eMMC interface. It will then look for a file called bootcode.bin on the primary partition (which must be FAT) to start booting the system. If it cannot access the SD/eMMC device or the boot code cannot be found, it will fall back to waiting for boot code to be written to it over USB; in other words, its USB port is in slave mode waiting to accept boot code from a suitable host.

A USB boot tool is available on Github which allows a host PC running Linux to write the BCM2837 boot code over USB to the module. That boot code then runs and provides access to the SD/eMMC as a USB mass storage device, which can then be read and written using the host PC. Note that a Raspberry Pi can be used as the host machine. For those using Windows a precompiled and packeged tool is available. For more information see here.

The Compute Module has a pin called EMMC_DISABLE_N which when shorted to GND will disable?the SD/eMMC interface (by physically disconnecting the SD_CMD pin), forcing BCM2837 to boot from USB. Note that when the eMMC is disabled in this way, it takes a couple of seconds from powering up for the processor to stop attempting to talk to the SD/eMMC device and fall back to booting from USB.?

意思很明顯了，CM3啟動的時候要去FAT文件系統找bootcode.bin，找不到就等待USB接口接收該文件。當前EMMC沒有系統，所以不使能EMMC。具體需要將EMMC_DISABLE_N管腳接地。對應下圖則將J4的跳線帽接到GND。

3.1.2 安裝驅動識別CM3

（1）安裝rpiboot_setup.exe 驅動。

（2）用USB連接CM3底板SLAVE接口。

（3）安裝之后，雙擊打開軟件，自動識別CM3并下發bootcode.bin。電腦出現外部存儲設備，此時CM3已經被抽象成存儲設備。

3.2、SDFormatter格式化CM3

同樹莓派格式步驟。

3.3、Win32DiskImager制作Linux鏡像

同樹莓派格式步驟。

總結

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