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STM32L151RB Rev V bootloader missing? (Rev W is fine)

Question asked by effeff on Jan 10, 2014
Latest reply on Jan 23, 2014 by Amel N
Hello,

I so far had no problems programming the STM32L151RBH6 via the serial bootloader and STMFlashLoader.exe.
Now new boards arrived with STM32L151RBH6 Rev W (device id 0x0416, revision 0x1078) and the serial bootloader is not functional.
(Previous MCU had mask Rev V (device id 0x0416, revision 0x1038)).

After checking various things I found that on the new boards the system memory (4kB where the bootloader should be) reads as zero!

On our previous devices (dev_id/rev_id 416/1038) the system memory is non-zero and the bootloader identification is a plausible 0x20 (at 0x1ff00ffe, decoding into: two USARTs are used, bootloader version 0).

Here are the dumps, with the new failing device first:

UID 3432471737373837208c878b dev_id/rev_id 416/1078
0x1ff00000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00
0x1ff00010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00
..
0x1ff00ff0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00



UID 313147103138303100837e85 dev_id/rev_id 416/1038
0x1ff00000  00 06 00 20 55 0c f0 1f  75 0c f0 1f 77 0c f0 1f
0x1ff00010  80 b5 00 f0 ad fd df f8  2c 04 00 68 00 21 81 80
..
0x1ff00ff0  00 00 00 00 00 00 00 00  00 00 00 00 30 00 20 00

This can be seen with a) ST-Link Utility or b) memory view within IAR debugger or c) when the microcontroller itself reads the corresponding area.

Among the things checked were: lowering baud rate, have PA12 non-floating (USB_DP, should be a non-issue on a non USB device with bootloader identification 0x20), adding external reset IC, updating STMFlashLoader.exe from v2.4.0 to v2.6.0, using Flash Loader Demo.
As the device has a 5mm x 5mm BGA package the access to the pins is very limited. Programming via SWD is fine. Unfortunately the system design heavily relies on a working serial bootloader.

What is going on? What are my options?

Thanks a lot,

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