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STM32F072 bootloader "limiitation".....

Question asked by wolff.roger on Jan 23, 2015
Latest reply on Feb 26, 2015 by waclawek.jan
Hi, 
I think I've found a "bug" in the bootloader. 
AN2606 documents for '051 chips on page 58 that: [quote] When the user application configures a value of HSI TRIM bits (in RCC_CR register) and then jumps to the  bootloader, the HSITRIM value is reset to its default value (0) at bootloader startup[/quote]
The same thing seems to happen for the 072 bootloader. 

But that isn't the problem... The problem is that the HSI TRIM default is not 0 but 16. This results in the CPU running about 40kHz * 16 = 640 kHz slower than the 1% calibrated 8MHz..... Apparently "autobauding" for the serial ports and "crystalless USB" end up compensating for this so that nobody has noticed that the bootloader runs at a multiple of 7.3MHz instead of 8MHz. 

All this isn't really a problem until you let the bootloader jump to your application and then end up with baud rates that are off by "too much". 

P.S. I checked the datasheet for the '51 and it too has "16" as the default HSITRIM. 

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