The aforementioned Github website of a private user repeats the same mistakes that were made with the so-called Blue Pill Board.
However, the official documentation from STMicroelectronics is decisive for the correct connection of the pins, e.g. from NRST, here e.g. the already mentioned AN2586, where you can read on page 11:
The STM32F1xx does not require an external reset circuit to power-up correctly. Only a pull-down capacitor is recommended to improve EMS performance by protecting the device against parasitic resets. See Figure 5.
Charging and discharging a pull-down capacitor through an internal resistor increases the device power consumption. The capacitor recommended value (100nF) can be reduced to 10nF to limit this power consumption.
In addition, both AN2586 (section 4.1) and AN2606 (section 15.1 and bootloader pattern 1 in table 2) mention that to successfully boot into system memory you must set BOOT0 to 1 and BOOT1 to 0. However, this is only relevant a few clock cycles after RESET:
The values on the BOOT pins are latched on the fourth rising edge of SYSCLK after a reset. It is up to the user to set the BOOT1 and BOOT0 pins after reset to select the required boot mode.
The start in the user flash area is usually the normal case, which is why BOOT0 is pulled down to logical 0. Since booting into the SRAM is extremely rare, BOOT1 can also be set to logic 0, either with a pull-down or fixed to GND.
For the less frequent starting of the boot loader in the system memory, a logical 1 at BOOT0 and a following short pulse at NRST is then only necessary.
In your circuit excerpt above under BOOTx settings, both BOOT pins float, which leads to very mysterious effects and must not be realised in this way under any circumstances - both BOOT pins, i.e. BOOT0 and BOOT1, require a fixed logic level.
Regards
/Peter
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