MAPR remaping with disable_jtag causes debugger to fail on stm32f103RGT6

[TheZoq2]

I recently got an XL density stm32f103 (stm32f103RGT6) and ran into a pretty strange issue.

When running the following code, the debugger stops responding and I have to reboot the microcontroller with BOOT0 pulled high in order to reflash it. The issue happens when configuring serial, when configuring SPI1 but not when configuring SPI2.

If mapr.mapr().modify(|_, w| w.spi1_remap().bit(PINS::REMAP)); is removed from spi.rs, things work fine which is a pretty clear indication that it is responsible.

Finally, removing disable_jtag also makes things work as normal

#![deny(unsafe_code)]
#![no_main]
#![no_std]

use panic_semihosting as _;

use stm32f1xx_hal::{
    prelude::*,
    pac,
    serial::{Config, Serial},
    spi::{Spi, Mode, Polarity, Phase}
};
use cortex_m_rt::entry;



#[entry]
fn main() -> ! {
    // Get access to the device specific peripherals from the peripheral access crate
    let p = pac::Peripherals::take().unwrap();

    let mut flash = p.FLASH.constrain();
    let mut rcc = p.RCC.constrain();

    let clocks=rcc.cfgr.freeze(&mut flash.acr);

    // Prepare the alternate function I/O registers
    let mut afio = p.AFIO.constrain(&mut rcc.apb2);

    // Prepare the GPIOB peripheral
    let mut gpioa = p.GPIOA.split(&mut rcc.apb2);
    let mut gpiob = p.GPIOB.split(&mut rcc.apb2);


    let (pa15, pb3, pb4) = afio.mapr.disable_jtag(gpioa.pa15, gpiob.pb3, gpiob.pb4);

    /*
    let right_usart = Serial::usart1(
        p.USART1,
        (
            gpioa.pa9.into_alternate_push_pull(&mut gpioa.crh),
            gpioa.pa10,
        ),
        &mut afio.mapr,
        Config::default().baudrate(921_600.bps()),
        clocks,
        &mut rcc.apb2,
    );
    */

    let mode = Mode{
        phase: Phase::CaptureOnFirstTransition,
        polarity: Polarity::IdleLow
    };
    let pins = (
        gpioa.pa5.into_alternate_push_pull(&mut gpioa.crl),
        gpioa.pa6,
        gpioa.pa7.into_alternate_push_pull(&mut gpioa.crl),
    );
    let mode = Mode{
        phase: Phase::CaptureOnFirstTransition,
        polarity: Polarity::IdleLow
    };

    let spi = Spi::spi1(p.SPI1, pins, &mut afio.mapr, mode, 1.khz(), clocks, &mut rcc.apb2);

    /*
    {
        let pins = (
            gpiob.pb13.into_alternate_push_pull(&mut gpiob.crh),
            gpiob.pb14,
            gpiob.pb15.into_alternate_push_pull(&mut gpiob.crh),
        );

        let spi = Spi::spi2(p.SPI2, pins, mode, 1.khz(), clocks, &mut rcc.apb1);
    }
    */
    loop {}
}

The same code works perfectly fine on the standard blue pill boards. This might also be a hardware issue, however as far as I know, the debug circuit on my custom PCB is the same as the blue pill.