Make a USB 2.0 OTG male type-A to male type-A cable and flush ANDROID OS or

RikoMagic RKM V3 TV stick microcomputers with RockChip ARM M53 architecture quad core microprocessor are in many ways similar to Raspberry Pi 4 and other micro PCs, but they also come with an inbuilt SSD and preinstalled Android operating system. The only thing remaining to do is to install your internet TV provider application from Google Play Store, or other software like computer games or even an internet banking application, if you also want to use the computer for other activities.

But as the time goes on newer versions of applications may not run on older versions of Android like 4.4, 5.0, 7.1, 8.0, etc. Though new Android versions source codes are readily available from Google, it is usually very difficult to tailor one to a particular hardware platform like RKM V3. A microcomputer manufacturer must also provide device drivers compatible with a newer Android version. Compiling a new Android version is still relatively difficult to do, therefore most manufacturers prefer to release update images and appropriate programming tools that we can use to flash a new Android version.

However, a new RKM V3 TV Stick come without USB OTG cable that is needed for an upgrade and there are not much useful instructions on the internet on how to build one at. RKM V3 microcomputer has a USB 2.0 and a USB 3.0 port, of witch USB 2.0 is OTG capable. But there are few USB cables with two male USB-A type connectors available from internet computer hardware stores. Most are intended for connecting external USB devices, and it might be dangerous to use them for inter-connecting two PCs. The reason why lays in +5 V power supply line that is usually intended to power an external device.

Making an USB OTG 2.0 cable with two male USB-A connectors

There is a variety for USB OTG Cables in the internet hardware stores, but none of them has two male USB-A type connectors that we need to flash RKM V3 TV Stick inbuilt SSD. Why? Computers each have their own power supply and should not be powered from a USB host. However, USB 2.0 type-A connectors only have 4 pins which make it impossible for a PC to indicate an OTG connection request to another computer hardware logic. If therefore both computers would have accidentally acted as USB 2.0 hosts (as they normally do), a slight voltage difference between USB power supply lines (ex. +5.1 V and +4.9 V) may cause a significant electric current to occur between computers, which may in turn damage USB controllers of one or both computers. An option to prevent this from happening is to inbuilt a 1 k Ohm resistor to the power supply line of an USB 2.0 connecting cable with two male USB-A connectors. This limits electric current, but still enables computers to indicate USB host status to a computer acting as an USB OTG device. It worked for me!

USB-A                          USB-A

+5V 1  <---- 1 k Ohm -------> 1   + 5 V

D+  2  <--------------------> 2   D+

D-  3  <--------------------> 3   D-

GND 4  <--------------------> 4   GND

case  <------------------------->  case

However, it is important to note that USB OTG 2.0 cable itself cannot be just a long stretch of a 4-lines flat cable, but a proper USB 2.0 cable must be used for cables longer than 5 cm. Though USB 2.0 cable without connectors is usually not as easy to buy as an Ethernet cable, cat. 5, 6 or 7, you may opt for a 5 m long USB extension cable with male and female USB-A connectors and cut it to shorter pieces as needed. It is not recommended a longer than 2 m USB cable for high speed connections, anyway.

How to flash Android OS image?

RikoMagic has provided a number of programming tools for Microsoft Windows as well as appropriate versions of Android and Linux operating systems images for their RKM TV boxes and TV sticks. A special RicoMagic provided micro SD card flashing tool can be used to make an SD card with Android upgrade image, which should perform an upgrade without the need for the USB OTG cable, but it hadn’t worked for me. The reason seems to be in a special RKM V3 operation mode called “Maskrom”, which can only be enabled though a USB OTG cable connection and RockChip provided Android programming tool (androidtool.exe). So, the cable seems to be needed at least as you are performing your first upgrade.

The steps needed to perform a successful upgrade are:

1.      Make a USB OTG cable with two male USB-A connectors and a 1 k Ohm resistor between +5 V pins.

2.      Get the latest Android OS image from www.rikomagic.com download site (ex. update_rk3328_9.0_RKM_public_20210520-1116.img).

3.      Get Driver Assistant package from www.rockchip.com download site (ex. DriverAssitant_v4.8.zip). Install the RockChip driver. Without it an USB OTG connection cannot be established during RKM V3 recovery boot and USB 2.0 port would instead establish a normal USB 2.0 host operation.

4.      Get Android Tool from www.rikomagic.com download site (ex. AndroidTool_Release v2.69.zip)

5.      Shutdown RKM V3 TV stick and unplug its power supply.

6.      Connect the TV stick with USB OTG 2.0 Cable mentioned above to a PC with Windows 7, 8 or 10 and RockChip driver installed and make sure that the PC is on and running. You may optionally open Devices and Printers window from Control Panel

7.      Find recovery boot button between the grill ribs on RKM V3 casing and hold it pushed down with a pencil or a small stick as you plug in the power cord. You may release the button only after RKM V3 boots into recovery mode.

8.      Start Android Tool and start programming the new Android OS image mentioned above. If all the programming steps succeed, RKM V3 microcomputer should be running a newer version of the Android OS after you restart it. However, if downloading the new Android OS image fails, but all the steps above succeed, continue to step 9.

9.      Go to the Advanced function tab in Android Tool and click “Go Maskrom” button. Then repeat steps 7 and 8. This will enable installing a fresh new version of Android OS but all the applications will have to be reinstalled.

How to flash Linux image?

Flashing Linux image is similar to flashing Android OS image, however upgrade is not possible and OS loader also has to be replaced. Complete EEPROM content must therefore be erased and re-flashed. Please, refer to the original RikoMagic instruction manual.