Can you try the below?
0. Connect HCI UART connection to PC.
1. Short SDA to GND
2. Power up the chip and wait for a couple of seconds or so.
3. Remove SDA to GND short.
4. Try downloading with -NODLMINIDRIVER.
It works thanks ! Why does the connection of the UART cable before powering up the chip fix the issue on my hardware ?
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Interesting. Glad to hear you have solved the problem. As to why.. I also wonder why, having had some experience with recovery recently.
The SDA must be grounded BEFORE booting the chip in order to be in recovery mode. In my configuration, connecting the USB to the PC is "equivalent" to powering the chip because during programming our board gets its power from the USB.
I suppose in your system you might have a separate power supply driving your BCM chip and the USB is used only for UART and not for chip power.
If that's the case then it makes sense that you have two separate independent steps for "Plug in USB" and "Power on Chip". The key thing to keep in mind is that the SDA must be grounded during the chip power up... which may be independent of the USB status.