The Compute module has an on-board eMMC device connected to the primary SD card interface. This guide explains how to write data to the eMMC storage using a Compute Module IO Board.
Please also read the section on Module booting and flashing the eMMC in the Compute Module Hardware Design Guide
To Flash the Compute Module eMMC you either need a Linux system (a Raspberry Pi is recommended, or Ubuntu on a PC) or a Windows sysem (Windows 7 recommended).
Note that there is a bug in the BCM2835 bootloader which returns a slightly incorrect USB packet to the host. Most USB hosts seem to ignore this benign bug and work OK, however we do see some USB ports that due to this bug do not work. We don't quite understand why some ports fail - it doesn't seem to be correlated with whether they are USB2 or USB3 (we have seen both types working) but is likely specific to the host controller and driver.
For Windows Users
Under Windows an installer is availble to automatically install the required drivers and boot tool. Alternatively a user can compile and run it using Cygwin and/or install the drivers manually.
For those who just want to enable the Compute Module eMMC as a mass storage device under Windows the standalone installer is the recommended option. This installer has been tested on Windows 7 32-bit and 64-bit. It also works under Windows 8 but you have to jump through some hoops as the driver is not signed, see here for instructions.
- Download and run the Windows installer to install the drivers and boot tool
- Plug your host PC USB into the CMIO USB SLAVE port making sure J4 is set to EN position
- Apply power to the CMIO board and Windows should now find the hardware and install the driver
- Once the driver install is complete run the RPiBoot.exe tool that was previously installed
- After a few seconds the Compute Module eMMC will pop up under Windows as a disk (USB mass storage device)
To use the tool under Cygwin on Windows firstly you'll need to install Cygwin. You'll need to make sure to install the libusb-1.0 and libusb-1.0-devel packages (NB tested using version 1.0.19-1) as well as gcc and Make.
You then need to install the Windows driver which can be downloaded here: bcm270x-boot-driver.zip. To install the driver firstly make sure that J4 (USB SLAVE BOOT ENABLE) is set to the 'EN' position, then plug the host machine into the Compute Module IO Board USB slave port (J15) and finally apply power to the CMIO board. Windows will see a new USB hardware device "BCM2708 Boot".
Select "Skip obtaining driver software from Windows Update" (or wait) and the driver will not be found. Close the dialog box.
Go to Windows Device Manager and you'll see an unknown device with a yellow exclamation mark under Other Devices->BCM2708 Boot
Right click on this unknown device and select "Update Driver Software", then select "Browse my computer for driver software". In the next dialog box select "Browse" and browse to the directory containing the unzipped bcm270x-boot-driver.zip (the directory containing bcm270x.inf) and select "Next". Finally click "Install this driver software anyway" when Windows complains it cannot verify the publisher.
After a short while the driver will finish being installed and you should be able to see it in Device Manager.
Finally follow the remainder of the instructions below (in a Cygwin terminal) Note that when performing the below commands in a Cygwin terminal don't prefix them with sudo.
On your Compute Module IO Board:
Make sure that J4 (USB SLAVE BOOT ENABLE) is set to the 'EN' position.
On your host system:
Git may produce an error if the date is not set correctly, so on a Raspberry Pi enter the following:
sudo date MMDDhhmmwhere MM is month, DD day and hh mm hours and minutes respectively.
Clone the usbboot tool repository:
git clone --depth=1 https://github.com/raspberrypi/tools
cd tools/usbbootlibusb must be installed. If you are using Cygwin please make sure libusb is installed as previously described. On the Raspberry Pi or other Debian based Linux:
sudo apt-get install libusb-1.0-0-devNow build and install the usbboot tool:
make
sudo make installRun the usbboot tool and it will wait for a connection:
sudo rpibootNow plug the host machine into the Compute Module IO Board USB slave port (J15) and power on the CMIO board. The rpiboot tool will discover the Compute Module and send boot code to allow access to the eMMC.
After rpiboot completes a new USB mass storage drive will appear in Windows. We recommend following this guide and using Win32DiskImager to write images to the drive, rather than trying to use /dev/sda etc. from Cygwin.
Once you have written an OS image make sure J4 (USB SLAVE BOOT ENABLE) is set to the disabled position and/or nothing is plugged into the USB slave port. Power cycling the IO board should result in the Compute Module booting the OS image from eMMC.
After rpiboot completes you will see a new device appear; this is commonly /dev/sda on a Pi but it could be another location such as /dev/sdb, so check in /dev/ before running rpiboot so you can see what changes.
You now need to write a raw OS image (such as Raspbian) to the device. Note the following command may take some time to complete, depending on the size of the image:
sudo dd if=raw_os_image_of_your_choice.img of=/dev/sda bs=4MiBOnce the image has been written, unplug and re-plug the USB; you should see 2 partitions appear (for Raspian) in /dev. In total you should see something similar to this:
/dev/sda <- Device
/dev/sda1 <- First partition (FAT)
/dev/sda2 <- Second partition (Linux filesystem)The /dev/sda1 and /dev/sda2 partitions can now be mounted normally.
Make sure J4 (USB SLAVE BOOT ENABLE) is set to the disabled position and/or nothing is plugged into the USB slave port. Power cycling the IO board should now result in the Compute Module booting from eMMC.