Unable to toggle GPIO PG12 on stm32l476 eval board

[Sean Link]

Currently unable to toggle the pin for the stm32 PG12 pin. My guess is power is not being enabled on port G for the board.

[David O'Connor]

Good catch. You are correct. Code was enabling port H instead of G. Fixed (on Github).

[Sean Link]

Can we reopen this? I am still unable to toggle this gpio. Looking at these directions...

If I try to follow step 1 & 2 using the following code

                        let pwr = unsafe { &(*crate::pac::PWR::ptr()) };
                        pwr.cr2.modify(|_, w| w.pvme2().set_bit());
                        while pwr.sr2.read().pvmo2().bit_is_set() {}
                        pwr.cr2.modify(|_, w| w.pvme2().clear_bit());
                        pwr.cr2.modify(|_, w| w.iosv().set_bit());

I hang on the while loop.

If I try to just set the iosv bit using

 pwr.cr2.modify(|_, w| w.iosv().set_bit());

the bit does not get set.

Any ideas?

[David O'Connor]

Strange! Are you able to get it working using the PAC directly?

[Sean Link]

No. I get the same result. Currently checking if this is a hardware configuration error like incorrect jumper pins set.

[Sean Link]

I got this working in the stm32l4xx-hal by modifying the blinky example. Looks to be a software problem.

[David O'Connor]

Is the port G RCC getting enabled in the RCC, as read using the PAC?

[Sean Link]

Yes.
Working stm32l4xx-hal

GPIOG Start
Register 0x48001800: 0xFDFFFFFF

AHB2 ENR Start
Register 0x4002104C: 0x00000040

AHB2 RSTR Start
Register 0x4002102C: 0x00000000

IOSV
Register 0x40007004: 0x00000200

stm32hal2

GPIOG Start
Register 48001800: 0xFDFFFFFF

AHB2 ENR Start
Register 4002104c: 0x00000044

AHB2 RSTR Start
Register 4002102c: 0x00000000

IOSV
Register 40007004: 0x00000000

[David O'Connor]

I've added the IOSV enable to GPIOG port enable on those L4 variants. I don't expect this to fix the problem because you already tried enabling it manually. But, it's a step in the right direction, since as you point out, this is a mandatory step. Might be worth trying again though with the update. (And checking, after you set up a Pin on Port G, that if IOSV stays enabled.

[Sean Link]

Same problem. Thanks for adding that change though. I am currently trying to find what other registers need to be set so the iosv bit can be enabled.

[Sean Link]

Okay figured it out.
I had to first enable power to the PWR peripheral. Then I was able to modify the iosv bit.

This is how I am using the code at its current revision. It would be nice If we could add the pwren() call inside the hal.

        let rcc = unsafe { &(*pac::RCC::ptr()) };
        rcc.apb1enr1.modify(|_, w| w.pwren().set_bit());
        let cs = Pin::new(Port::G, 12, PinMode::Output);

[Sean Link]

Same thing holds true for USB initialization. Need to enabled power, then change the usv bit. Note that changing the usv or iosv bit required me to re-enable power to PWR between bit toggles of usv and iosv.

[Sean Link]

To be more explicate...

        // Enable Port G Power
        let rcc = unsafe { &(*pac::RCC::ptr()) };
        rcc.apb1enr1.modify(|_, w| w.pwren().set_bit());

        let cs = Pin::new(Port::G, 12, PinMode::Output);

        // Enable Usb Power
        rcc.apb1enr1.modify(|_, w| w.pwren().set_bit()); // <- Was not able to ommit this line even though I already call pwren().set_bit().
        let pwr = unsafe { &*PWR::ptr() };
        pwr.cr2.modify(|_, w| w.usv().set_bit());

[Sean Link]

I'm going to make changes to the call and submit a PR if everything works.

[Sean Link]

Can now use the above example in the following way...

        // Note: No more low level register configurations to the user of the hal.
        let cs = Pin::new(Port::G, 12, PinMode::Output);

        // Note: User is still on the hook to properly configure pwr when working with USB. This could definitely be a future improvement when working with USB.
        // Enable Usb Power
        rcc.apb1enr1.modify(|_, w| w.pwren().set_bit());
        let pwr = unsafe { &*PWR::ptr() };
        pwr.cr2.modify(|_, w| w.usv().set_bit());

[David O'Connor]

Great stuff!