embassy-rs/embassy · error

QSPI data is empty, so the data width should be NONE

Error message

QSPI data is empty, so the data width should be NONE

What it means

In setup_transaction, embassy-stm32's QSPI driver requires that when no data bytes are transferred (data_len is None), the transaction's data width (dwidth) must be QspiWidth::NONE. If you pass no data but a non-NONE width, the driver panics because the hardware config would be inconsistent. It is a fail-fast invariant check on the command/transaction configuration.

Solutions

1. Set dwidth: QspiWidth::NONE on the command whenever no data bytes are transferred.
2. If data should be sent, provide a non-empty buffer/length (Some(len), len >= 1) matching the dwidth.
3. Validate at construction: ensure (data_len.is_some() == (dwidth != QspiWidth::NONE)) before calling the blocking APIs.

Example fix

// before
let mut cmd = QspiCommand::new(instruction, QspiWidth::SING);
cmd.data_width = QspiWidth::QUAD; // data_len is None -> panic
qspi.blocking_command(cmd);
// after
let mut cmd = QspiCommand::new(instruction, QspiWidth::SING);
cmd.data_width = QspiWidth::NONE; // no data phase
qspi.blocking_command(cmd);

assert_eq!(
    cmd.args.data.is_some(),
    cmd.data_width != QspiWidth::NONE,
    "QSPI: data phase presence must match data width"
);
assert!(cmd.args.data.as_ref().map_or(true, |d| !d.is_empty()), "QSPI: data must be at least one byte");

fn has_consistent_data_phase(cmd: &QspiCommand) -> bool {
    match (cmd.args.data.as_ref().map(|d| d.len()), cmd.data_width) {
        (Some(0), _) | (Some(_), QspiWidth::NONE) => false,
        (None, QspiWidth::NONE) | (Some(_), _) => true,
        (None, _) => false,
    }
}

When it happens

Trigger: Calling blocking_read, blocking_write, setup_auto_poll, or setup_command with a QspiCommand whose data phase is omitted (no buffer/length) while transaction.dwidth is set to something other than QspiWidth::NONE. Related panics in the same match: Some(0) length, or Some(len) with QspiWidth::NONE, also panic.

Common situations: Copying a command struct from an example that sent data but stripping out the buffer without resetting dwidth; building commands dynamically where the data field is Option and the width is hardcoded; mixing up the alternate/instruction width with the data width.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• Can only take the executor once
• DMA data error
• MCLK frequency < 9.5 MHz is not compatible with the TRNG
• Unknown value
• Invalid value

AI-assisted analysis of embassy-rs/embassy@463a07b963 (2026-09-10). Data as JSON: /api/errors/9ab5d5eaa0cc73ad. Report an issue: GitHub.

Appendix: source

Thrown at embassy-stm32/src/qspi/mod.rs:387

        match (transaction.address, transaction.awidth) {
            (Some(_), QspiWidth::NONE) => panic!("QSPI address can't be sent with an address width of NONE"),
            (Some(address), _) => {
                // u32::bit_width was only stabilized in 1.97
                let address_bit_width = u32::BITS - address.leading_zeros();
                if address_bit_width > transaction.address_size.bit_width() as u32 {
                    panic!("QSPI address too large to be represented with the given address size");
                }
            }
            (None, QspiWidth::NONE) => {}
            (None, _) => panic!("QSPI address is not set, so the address width should be NONE"),
        }

        match (data_len, transaction.dwidth) {
            (Some(0), _) => panic!("QSPI data must be at least one byte"),
            (Some(_), QspiWidth::NONE) => panic!("QSPI data can't be sent with a data width of NONE"),
            (Some(_), _) => {}
            (None, QspiWidth::NONE) => {}
            (None, _) => panic!("QSPI data is empty, so the data width should be NONE"),
        }

        T::REGS.fcr().modify(|v| {
            v.set_csmf(true);
            v.set_ctcf(true);
            v.set_ctef(true);
            v.set_ctof(true);
        });

        while T::REGS.sr().read().busy() {}

        if let Some(len) = data_len {
            T::REGS.dlr().write(|v| v.set_dl(len as u32 - 1));
        }

        T::REGS.ccr().write(|v| {
            v.set_fmode(fmode.into());
            v.set_imode(transaction.iwidth.into());

View on GitHub (pinned to 463a07b963)