Read corruption for stm32f42xxG and stm32f43xxG in dual…

Error message

Read corruption for stm32f42xxG and stm32f43xxG in dual bank mode when PA12 is in use for chips below revision 3, see errata 2.2.11

What it means

Same errata 2.2.11 as the I-variant case, but for STM32F42x/43xG 1MB parts when the flash is in dual-bank mode: reading the second bank with rev_id below revision 3 while PA12 is not an output driven low corrupts reads. Embassy panics to avoid returning silently corrupted data.

Solutions

Drive PA12 as a low output before any flash access on affected revisions.
Use silicon revision 3+ parts where errata 2.2.11 is fixed.
Reconfigure the option bytes to single-bank mode (db1m) so second-bank reads never occur, if 1MB single-bank fits your needs.
Pick a different pin for USB/GPIO functions so PA12 stays tied low during flash operations.

Example fix

// before
let mut flash = Flash::new(p.FLASH); // dual-bank G variant, PA12 in use, rev<3: panics
// after
let mut pa12 = Output::new(p.PA12, Level::Low, Speed::Low);
drop(pa12); // ensure PA12 is output-low before flash use
let mut flash = Flash::new(p.FLASH);

Defensive patterns

Strategy: validation

Validate before calling

// guard: only perform second-bank reads when safe
fn second_bank_read_safe(rev_id: u16, pa12_low: bool, dual_bank: bool) -> bool {
    !(dual_bank && rev_id < 3 && !pa12_low)
}

Prevention

Avoid PA12 (USB D+) duty on 1MB dual-bank F42x/43xG parts below rev 3
Use single-bank option-byte config when dual-bank is not required
Verify chip revision early in bring-up

When it happens

Trigger: Second-bank flash read on stm32f42xxG/stm32f43xxG with rev_id < REVISION_3, dual-bank mode active, and PA12 not configured as output-pull-low.

Common situations: 1MB F4 chips configured dual-bank via the db1m option byte, PA12 used for USB or GPIO, flash operations on early silicon revisions.

Understand the failure class

Background: "unsupported platform" / "not supported on this platform" errors: what they mean and how to fix them — this error's family across 47 libraries.

Related errors

AI-assisted analysis of embassy-rs/embassy@463a07b963 (2026-09-10). Data as JSON: /api/errors/2ba11410e253b70a. Report an issue: GitHub.

Appendix: source

Thrown at embassy-stm32/src/flash/f4.rs:275

        feature = "stm32f427vg",
        feature = "stm32f427zg",
        feature = "stm32f429ag",
        feature = "stm32f429bg",
        feature = "stm32f429ig",
        feature = "stm32f429ng",
        feature = "stm32f429vg",
        feature = "stm32f429zg",
        feature = "stm32f437ig",
        feature = "stm32f437vg",
        feature = "stm32f437zg",
        feature = "stm32f439bg",
        feature = "stm32f439ig",
        feature = "stm32f439ng",
        feature = "stm32f439vg",
        feature = "stm32f439zg",
    ))]
    if second_bank_read && pac::DBGMCU.idcode().read().rev_id() < REVISION_3 && !pa12_is_output_pull_low() {
        panic!(
            "Read corruption for stm32f42xxG and stm32f43xxG in dual bank mode when PA12 is in use for chips below revision 3, see errata 2.2.11"
        );
    }
}

#[allow(unused)]
fn pa12_is_output_pull_low() -> bool {
    use pac::GPIOA;
    use pac::gpio::vals;
    const PIN: usize = 12;
    GPIOA.moder().read().moder(PIN) == vals::Moder::Output
        && GPIOA.pupdr().read().pupdr(PIN) == vals::Pupdr::PullDown
        && GPIOA.odr().read().odr(PIN) == vals::Odr::Low
}

#[cfg(test)]
mod tests {
    use super::*;

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