Solved
I am using an STM32F103Z MCU. I cannot get Port B Pin 4 to work as a normal GPIO output pin. I do the setup just like other GPIO pins that are working, but Port B Pin 4 just goes high and stays high, GPIO_ResetBits() does not work.
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// Disable the JTAG portion of the Serial Wire JTAG Debug Port SWJ-DP
GPIO_PinRemapConfig(GPIO_Remap_SWJ_JTAGDisable, ENABLE);Enter your E-mail address. We'll send you an e-mail with instructions to reset your password.