embassy-rs/embassy · error

Bank 1 not present

Error message

Bank 1 not present

What it means

This panic is generated into the flash driver when the chip's metadata contains no FLASH_BANK_1 region, so the generated bank-1 accessor has no address and falls back to `panic!("Bank 1 not present")`. It fires at runtime if flash bank-1 code is called on a chip that has no flash bank 1 defined in embassy-stm32's per-chip data.

Solutions

1. Verify you built for a chip that actually has flash bank 1; if so, check embassy-stm32's data for that chip's memory regions.
2. Use the correct chip feature name matching your MCU so the right memory map is selected.
3. If the chip does have bank 1 but metadata lacks it, report/patch embassy-stm32's per-chip data (memory map definition).

Example fix

# before
features = ["stm32h743xx"]  # wrong variant, no bank1 modeled
# after
features = ["stm32h743zi"]  # correct variant with flash bank 1

// Only use flash bank APIs on chips with bank 1 modeled:
// verify region FLASH_BANK_1 exists for your chip feature in embassy-stm32 data

When it happens

Trigger: Calling flash APIs (e.g. `flash::blocking::Flash::new` or bank functions) on a chip whose memory-map data lacks a bank-1 region, so `bank_1_base` is None when build.rs generates the constant.

Common situations: Using the flash driver on chips where flash banks aren't modeled (RAM-only or unusual parts); chip metadata gaps after adding a new MCU; wrong chip cargo feature selected.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

• Bank 2 not present
• OTP not present
• Both 'single-bank' and 'dual-bank' features enabled
• Chip supports single and dual bank configuration. No Cargo…
• attempted to use peripheral

AI-assisted analysis of embassy-rs/embassy@463a07b963 (2026-09-10). Data as JSON: /api/errors/d36501223c427999. Report an issue: GitHub.

Appendix: source

Thrown at embassy-stm32/build.rs:541

                            .any(|f| f.name == "Memrmp" && f.fields.iter().any(|f| f.name == "fb_mode"))
                    })
            });

        let mut bank_1_base = None;
        let mut bank_2_base = None;
        let mut otp_base = None;
        for region in flash_memory_regions.iter() {
            if region.name == "BANK_1" || region.name == "BANK_1_REGION_1" {
                bank_1_base = Some(region.address);
            } else if region.name == "BANK_2" || region.name == "BANK_2_REGION_1" {
                bank_2_base = Some(region.address);
            } else if region.name == "OTP" {
                otp_base = Some(region.address);
            }
        }
        let bank_1 = bank_1_base
            .map(|a| quote!(#a))
            .unwrap_or_else(|| quote!(panic!("Bank 1 not present")));
        let bank_2 = bank_2_base
            .map(|a| quote!(#a))
            .unwrap_or_else(|| quote!(panic!("Bank 2 not present")));
        let otp = otp_base
            .map(|a| quote!(#a))
            .unwrap_or_else(|| quote!(panic!("OTP not present")));

        let (swap_check, bank1, bank2) = if check_fb_mode {
            (
                quote! { let is_swapped = crate::pac::SYSCFG.memrmp().read().fb_mode(); },
                quote! { if is_swapped { #bank_2 } else { #bank_1 } },
                quote! { if is_swapped { #bank_1 } else { #bank_2 } },
            )
        } else {
            (quote! {}, quote! { #bank_1 }, quote! { #bank_2 })
        };

        flash_regions.extend(quote! {

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