How-To: Writing an image to your eMMC Module
So, you’ve just received that single board computer and eMMC module that you have been anxiously awaiting, unboxed it, and gathered the peripherals and cables to connect it. So now what? It will not function without a compatible OS flashed (written) to your eMMC. Where do you start? What methods can you use to write this image? More importantly, what hardware will be needed?
Your PC or Mac has no way to directly interface with an eMMC (embedded Multi-Media Controller) module, so there will always be a need for an eMMC adapter or reader/writer module of some sort. This is an evaluation and comparison of the different types of this hardware that we offer in our store.
eMMC Adapter and microSD Card Reader
This is undoubtedly the most universally effective method of writing information to an eMMC. An eMMC adapter is a tiny PCB board with basically the same form factor as a typical microSD card, with an eMMC connector pin strip to attach an eMMC to it. As such, this adapter will insert into any SD card reader with a microSD slot. Now, it is definitely worth mentioning that all microSD card readers are not created equal, and some will simply not recognize an eMMC module or the eMMC adapter. Thankfully, community developers have begun documenting lists of card readers that are compatible with eMMC modules and adapters. One list of compatible card readers that is quite formulative is available on the HardKernel forums here:
The eMMC module must be attached to the pin strip of the adapter (in the correct orientation), and then inserted into the microSD slot of the reader, which is in turn inserted into an available USB port on your PC or Mac. At this point, assuming you are using a compatible card reader, your eMMC module will appear as a selectable disk drive on your computer. You should now be able to use your preferred image writing software to access, read, and write an OS to your eMMC, as long as the eMMC is properly formatted and “clean”. If the eMMC is not visible, not accessible or not able to be written to, you may need to “clean” the module using diskpart (we will discuss this process in the troubleshooting section at the end of this blog).
USB 2.0 Module Writer
Obviously, eMMC module writers boast a somewhat simpler approach to reading and writing to eMMC modules as well as faster read/write speeds, but there can be problems that arise when it comes to compatibility with eMMC modules. Pine Microsystems manufactures the USB 2.0 eMMC Module Writer, shown in the photo above. An eMMC module attaches directly to the module writer (the eMMC mounted in the correct orientation should cover the silver rectangle), eliminating the need for an SD card reader, or an eMMC adapter. This device then inserts directly into an available USB slot on your PC or Mac, at which point the eMMC should be visible to your computer. You should again be able to use your image writing software to read and write to the eMMC, allowing you to flash the necessary OS image for your SBC.
Although this writer has exhibited no evidence of incompatibility with hardware or software, it should be mentioned that it has not been tested with all eMMC compatible boards. Still the performance of this eMMC writer has proved to be consistent.
USB 3.0 Module Writer
The fastest adapter/writer available for writing OS images to eMMC modules is the USB 3.0 Module Writer, manufactured by HardKernel (the folks who brought you the ODROID line of SBCs). As the name suggests, it uses the USB 3.0 Superspeed standard, and can subsequently read, and write to eMMCs at much greater speeds (3x-4x faster) than the aforementioned eMMC writing hardware. Again the eMMC module attaches directly to the PCB (above the outlined box labeled eMMC) and inserts directly into an available USB 3.0 (or 2.0) slot on your PC or Mac for use with your image writing software.
It should be noted that this eMMC module writer has encountered some compatibility issues with certain eMMC modules, particularly (but not limited to) eMMCs not manufactured by HardKernel. There is an incompatibility issue with the Black eMMC modules manufactured by HardKernel. Therefore, the USB 3.0 eMMC Module Writer will not read or write to the Pine64 eMMCs or the black Hardkernel eMMCs.
Properly formatting and cleaning eMMCs for use
Sometimes, an eMMC module can’t be formatted or shows the wrong capacity, making it virtually impossible to properly flash an image to it. If your eMMC is exhibiting these behaviors, or just isn’t working quite right, “cleaning” the drive and removing its partitions is one possible solution. To perform this operation in Windows, you will need to open a command prompt terminal, and use the “diskpart” utility to completely format the eMMC, removing hidden partitions and erasing all data. Here is a link to a guide for using the diskpart utility to clean any eMMC, as well as SD cards and USB flash drives:
With the proper hardware and preparation discussed in this article, you should now be ready to flash the image of your choice to the appropriate eMMC for your SBC, and get it booted and running!