Very often in the latest months the same problem pops out in social media.
For other problems I have a dedicated page on my blog but for this one, I made a distinct one.
Xiegu G90 owners complain about bricking the radio while trying to downgrade it to 1.77 FW revision (or earlier revision). The "COMM LOST" after uploading the firmware is the main indication for this kind of problem.
While the problem and the solution is simple, the problem is not enough explained by neither XIEGU or their representatives in the market.
So, this is how the things are:
First, the Chinese manufacturer switched from the original STM32F103 to GD32F103 chip in the Front panel unit (they also made the same thing into the Main Unit MCU).
GD32xxx are perceived as cheap Chinese clones of ST original ones but the reality is a little bit more complicated and the GD MCU "appears to be a faster, more capable version of the STM32F103".
There are significant improvements in the inner architecture that makes GD MCU more attractive for this application (and the price factor also is a plus).
But the choice of the GD chip have some consequences.
One of them is the way that the FW is uploaded...
The upload process is managed by a small program called BOOTLOADER which resides in an area of memory to which the user has no access. It determines the sequence of operations that the chip performs when it is powered.
In the case of STM, a sequence is automatically executed at power-up which, for a short time, waits for an upload command on the UART port accessible to the user. Once the correct command is received on this port, the BOOTLOADER executes some predefined commands, such as clearing the existing FW from memory and loading the new FW.
In the case of the GD chip, in order to access the FW loading procedure, the user must execute a preset combination of buttons when turning on the radio.
Most likely, this method was chosen to eliminate errors caused by accidentally starting the radio with the data cable connected.
The differences in the internal architecture of the two chips and the modification of the BOOTLOADER required some changes in the FW; since it is proprietary and I don't have access to the source code, it is hard to say how the SW engineers solved these problems concretely.
But it is obvious that the SW versions released after the implementation of the HW modification take into account both versions because ST chip platforms can use all SW versions without problems.
As for models equipped with GD chip, they are identified by the letter "V" in the serial number to differentiate them from those with ST chip.
In the FW update archives, the manufacturer was considerate enough to include a note about the improvements to the released version but, as we are radio amateurs, we have the bad habit of not reading them!
If we would just read them, we would learn interesting things, such as those about HW version compatibility.
What that means?
Well, 1.77b is the FW revision where the compatibility issue was solved and this FW is working on both version of HW, GD and STM.
Above this version, all HW are compatible but below this, the FW can run only on ST equipped radios.
The BOOTLOADER is a little bit dumb; it's job is just to open the UART "door" to the user and let the new FW to get into the FLASH memory of the MCU (eventually decrypt it) but cannot check if the FW is compatible with the inner architecture of the chipset.
Therefore, the user will see a "UPLOAD SUCCESSFULL" onto the PC screen but a bricked radio on his desk!
The solution is very simple because, being dumb, the BOOTLOADER will act in the same way when the BOOT FW sequence is applied at the start but it will be a good choice to completely shut down the power supply.
To sum up:
-CHECK THE HARDWARE VERSION of your radio from it's serial number.
-If the serial number is above X04G211600001 or have a "V", do not use FW version below 1.77.
-If you "bricked" the radio or you have a "COMM LOST" after uploading the FW into the MAIN UNIT, upgrade the FW at least to 1.77b. Make sure you have a compatible Front Panel - Main Unit FW combination.
Don't be afraid to use the official page of XIEGU; it is in Chinese but these days automatic translation makes wonders!
Cheers,
Adrian
