Main thread panic on flash (?)

[Doloro1978]

Hihi, im trying to flash my esp32 dev board but i keep running into an error

Running `espflash flash --monitor target/xtensa-esp32-espidf/debug/ir`
[2025-08-10T14:41:39Z INFO ] Serial port: '/dev/ttyUSB0'
[2025-08-10T14:41:39Z INFO ] Connecting...
[2025-08-10T14:41:39Z INFO ] Using flash stub
Error:   × Main thread panicked.
  ├─▶ at /home/doloro/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/serialport-4.7.2/src/posix/tty.rs:499:9
  ╰─▶ assertion failed: termios2.c_ospeed == termios2.c_ispeed
  help: set the `RUST_BACKTRACE=1` environment variable to display a backtrace.

I'm on espflash 4.0.1 with Linux 6.15.9-arch1-1

[SergioGasquez]

• Can you share the full log with debug? RUST_LOG=debug cargo run --release
• Do you have modified the baudrate? Could you test with a different baud with -B, --baud?

[LLeny]

Facing the same issue with espflash 4.0.1 and Linux 6.15.9-arch1-1. It's a recent issue.
Tried with different baud rates, no luck.

        FlashArgs {
            connect_args: ConnectArgs {
                after: HardReset,
                baud: Some(
                    9600,
                ),
                before: DefaultReset,
                chip: None,
                confirm_port: false,
                list_all_ports: false,
                no_stub: false,
                port: None,
                non_interactive: false,
            },
            flash_config_args: FlashConfigArgs {
                flash_freq: None,
                flash_mode: None,
                flash_size: None,
            },
            flash_args: FlashArgs {
                monitor: false,
                monitor_args: MonitorConfigArgs {
                    monitor_baud: 115200,
                    elf: None,
                    no_reset: false,
                    log_format: None,
                    output_format: None,
                    processors: None,
                },
                ram: false,
                no_verify: false,
                no_skip: false,
                image: ImageArgs {
                    min_chip_rev: 0,
                    mmu_page_size: None,
                    check_app_descriptor: true,
                },
                erase_parts: None,
                erase_data_parts: None,
            },
            image: "reather",
            format: EspIdf,
            idf_format_args: IdfFormatArgs {
                bootloader: None,
                partition_table: None,
                partition_table_offset: None,
                target_app_partition: None,
            },
        },
    ), false
[2025-08-13T04:05:27Z DEBUG] connecting to crates.io:443 at 18.64.67.105:443
[2025-08-13T04:05:27Z DEBUG] No cached session for DnsName("crates.io")
[2025-08-13T04:05:27Z DEBUG] Not resuming any session
[2025-08-13T04:05:27Z DEBUG] Using ciphersuite TLS13_AES_128_GCM_SHA256
[2025-08-13T04:05:27Z DEBUG] Not resuming
[2025-08-13T04:05:27Z DEBUG] TLS1.3 encrypted extensions: [ServerNameAck]
[2025-08-13T04:05:27Z DEBUG] ALPN protocol is None
[2025-08-13T04:05:27Z DEBUG] created stream: Stream(RustlsStream)
[2025-08-13T04:05:27Z DEBUG] sending request GET https://crates.io/api/v1/crates/espflash/versions
[2025-08-13T04:05:27Z DEBUG] writing prelude: GET /api/v1/crates/espflash/versions HTTP/1.1
    Host: crates.io
    User-Agent: ureq/2.12.1
    Accept: */*
    accept-encoding: gzip
[2025-08-13T04:05:28Z DEBUG] Chunked body in response
[2025-08-13T04:05:28Z DEBUG] response 200 to GET https://crates.io/api/v1/crates/espflash/versions
[2025-08-13T04:05:28Z DEBUG] dropping stream: Stream(RustlsStream)
[2025-08-13T04:05:28Z DEBUG] Config: ProjectConfig {
        baudrate: None,
        format: EspIdf,
        idf_format_args: IdfFormatArgs {
            bootloader: None,
            partition_table: None,
            partition_table_offset: None,
            target_app_partition: None,
        },
        flash: FlashSettings {
            mode: None,
            size: None,
            freq: None,
        },
    }
[2025-08-13T04:05:28Z DEBUG] Port Config: PortConfig {
        connection: Connection {
            serial: None,
        },
        usb_device: [
            UsbDevice {
                vid: 6790,
                pid: 29986,
            },
        ],
        save_path: "~/.config/espflash/espflash_ports.toml",
    }
[2025-08-13T04:05:28Z WARN ] Monitor options were provided, but `--monitor/-M` flag isn't set. These options will be ignored.
[2025-08-13T04:05:28Z INFO ] Serial port: '/dev/ttyUSB0'
[2025-08-13T04:05:28Z INFO ] Connecting...
[2025-08-13T04:05:28Z DEBUG] Using UnixTight reset strategy with delay of 50ms
[2025-08-13T04:05:28Z DEBUG] Boot Mode: 0x3
[2025-08-13T04:05:28Z DEBUG] Download Mode: true
[2025-08-13T04:05:28Z DEBUG] Writing command: Sync
[2025-08-13T04:05:28Z DEBUG] Writing command: Sync
[2025-08-13T04:05:28Z DEBUG] Writing command: ReadReg { address: 40001000 }
[2025-08-13T04:05:28Z DEBUG] Writing command: ReadReg { address: 40001000 }
[2025-08-13T04:05:28Z DEBUG] Read chip magic value: 0x00f01d83
[2025-08-13T04:05:28Z INFO ] Using flash stub
[2025-08-13T04:05:28Z DEBUG] Loading flash stub for chip: Esp32
[2025-08-13T04:05:28Z DEBUG] Write 3532 byte stub text
[2025-08-13T04:05:28Z DEBUG] Writing command: MemBegin { size: dcc, blocks: 01, block_size: 1800, offset: 400be000, supports_encryption: false }
[2025-08-13T04:05:28Z DEBUG] Writing command: MemData { data: [08, ..., 00], pad_to: 04, pad_byte: 00, sequence: 00 }
[2025-08-13T04:05:28Z DEBUG] Write 156 byte stub data
[2025-08-13T04:05:28Z DEBUG] Writing command: MemBegin { size: 9c, blocks: 01, block_size: 1800, offset: 3ffdeba8, supports_encryption: false }
[2025-08-13T04:05:28Z DEBUG] Writing command: MemData { data: [0c,..., 40], pad_to: 04, pad_byte: 00, sequence: 00 }
[2025-08-13T04:05:28Z DEBUG] Finish stub write
[2025-08-13T04:05:28Z DEBUG] Writing command: MemEnd { no_entry: false, entry: 400be5ec }
[2025-08-13T04:05:28Z DEBUG] Stub written!
[2025-08-13T04:05:28Z DEBUG] Writing command: ReadReg { address: 40001000 }
[2025-08-13T04:05:28Z DEBUG] Read chip magic value: 0x00f01d83
[2025-08-13T04:05:28Z DEBUG] Re-detected chip: Esp32
[2025-08-13T04:05:28Z DEBUG] Attempting flash enable with: SpiAttachParams { clk: 0, q: 0, d: 0, hd: 0, cs: 0 }
[2025-08-13T04:05:28Z DEBUG] Writing command: SpiAttachStub { spi_params: SpiAttachParams { clk: 00, q: 00, d: 00, hd: 00, cs: 00 } }
[2025-08-13T04:05:28Z DEBUG] Writing command: ReadReg { address: 3ff4201c }
[2025-08-13T04:05:28Z DEBUG] Writing command: ReadReg { address: 3ff42024 }
[2025-08-13T04:05:28Z DEBUG] Writing command: WriteReg { address: 3ff4201c, value: 90000000, mask: None }
[2025-08-13T04:05:28Z DEBUG] Writing command: WriteReg { address: 3ff42024, value: 7000009f, mask: None }
[2025-08-13T04:05:28Z DEBUG] Writing command: WriteReg { address: 3ff4202c, value: 17, mask: None }
[2025-08-13T04:05:28Z DEBUG] Writing command: WriteReg { address: 3ff42080, value: 00, mask: None }
[2025-08-13T04:05:28Z DEBUG] Writing command: WriteReg { address: 3ff42000, value: 40000, mask: None }
[2025-08-13T04:05:28Z DEBUG] Writing command: ReadReg { address: 3ff4201c }
[2025-08-13T04:05:28Z DEBUG] Writing command: ReadReg { address: 3ff42080 }
[2025-08-13T04:05:28Z DEBUG] Writing command: WriteReg { address: 3ff4201c, value: 80000040, mask: None }
[2025-08-13T04:05:28Z DEBUG] Writing command: WriteReg { address: 3ff42024, value: 70000000, mask: None }
[2025-08-13T04:05:28Z DEBUG] Flash detect OK!
[2025-08-13T04:05:28Z DEBUG] Writing command: SpiSetParams { spi_params: SpiSetParams { fl_id: 00, total_size: 400000, block_size: 10000, sector_size: 1000, page_size: 100, status_mask: ffff } }
[2025-08-13T04:05:28Z DEBUG] Writing command: ReadReg { address: 3ff6607c }
[2025-08-13T04:05:28Z DEBUG] Writing command: ReadReg { address: 3ff5a00c }
[2025-08-13T04:05:28Z DEBUG] Writing command: ReadReg { address: 3ff5a014 }
[2025-08-13T04:05:28Z DEBUG] Writing command: ReadReg { address: 3ff5a014 }
[2025-08-13T04:05:28Z DEBUG] Writing command: ReadReg { address: 3ff40014 }
Error:   × Main thread panicked.
  ├─▶ at ~/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/serialport-4.7.2/src/posix/tty.rs:499:9
  ╰─▶ assertion failed: termios2.c_ospeed == termios2.c_ispeed

[SergioGasquez]

I was just able to reproduce the error, Ill do some investigation, in the meantime, using --baud 9600 seems to be a workaround for the issue

[LLeny]

I was just able to reproduce the error, Ill do some investigation, in the meantime, using --baud 9600 seems to be a workaround for the issue

Sadly the 9600 baud doesn't do it for me. That log was at 9600.

[SergioGasquez]

Can you try modifying ~/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/serialport-4.7.2/src/posix/tty.rs:499:9? I added a few prints:

    fn baud_rate(&self) -> Result<u32> {
        let termios2 = ioctl::tcgets2(self.fd)?;

        println!("termios2.c_ospeed: {}", termios2.c_ospeed);
        println!("termios2.c_ispeed: {}", termios2.c_ispeed);

        assert!(termios2.c_ospeed == termios2.c_ispeed);

        Ok(termios2.c_ospeed)
    }

And noticed the following

[2025-08-13T08:32:31Z DEBUG] Change baud to: 921600
termios2.c_ospeed: 115200
termios2.c_ispeed: 9600

[LLeny]

Got:

termios2.c_ospeed: 115200
termios2.c_ispeed: 9600

monitor works but not flashing.

[Soblow]

I have the same issue while attempting to flash an ESP32C6 board on Arch Linux (kernel 6.16.1-arch1-1).
Removing the assertion, and reinstalling espflash fixes the issue on my end, and the flashing works perfectly fine.

[orhun]

Arch Linux maintainer of the espflash package here 👋🏼
I happen to experience the same issue with ESP32 T-Display. Patching the dependency is not an option for the binary package so I was wondering if there is any other patch/workaround we could apply on top of espflash in the meantime?

[sirhcel]

A maintainer of serialport-rs here 👋. We've received PR serialport/serialport-rs#283 which fixes the issue for the author and we are are looking for a a second opinion from using it with espflash.

I can't reproduce this issue on my systems. But I've set up at test branch of espflash with a modified serialport dependency with this fix: https://github.com/sirhcel/espflash/tree/test/fix-serialport-panic-pr-283 Could someone please give it a spin? Looking with my faithful dog eyes at @Soblow, @SergioGasquez, and @orhun. 😅

I happen to experience the same issue with ESP32 T-Display. Patching the dependency is not an option for the binary package so I was wondering if there is any other patch/workaround we could apply on top of espflash in the meantime?

Would a patch release of serialport-rs allow you to progress resolving this issue on Arch @orhun?

[Soblow]

I can't reproduce this issue on my systems. But I've set up at test branch of espflash with a modified serialport dependency with this fix: https://github.com/sirhcel/espflash/tree/test/fix-serialport-panic-pr-283 Could someone please give it a spin? Looking with my faithful dog eyes at @Soblow, @SergioGasquez, and @orhun. 😅

Oh, that's convenient for testing, thank you!
I've just tested on my end, installing your forked repo ( cargo install --git https://github.com/sirhcel/espflash --branch test/fix-serialport-panic-pr-283 ) and it works perfectly fine.

Replacing /home/$USER/.cargo/bin/espflash
    Replaced package `espflash v4.0.1 (/home/$USER/Downloads/espflash/espflash)` with `espflash v4.0.1 (https://github.com/sirhcel/espflash?branch=test%2Ffix-serialport-panic-pr-283#7ff37a26)` (executable `espflash`)

    Finished `dev` profile [optimized + debuginfo] target(s) in 0.34s
     Running `espflash flash --monitor target/xtensa-esp32-espidf/debug/ledstrip`
[2025-08-24T10:12:13Z INFO ] Serial port: '/dev/ttyUSB0'
[2025-08-24T10:12:13Z INFO ] Connecting...
[2025-08-24T10:12:13Z INFO ] Using flash stub
Chip type:         esp32 (revision v3.1)
Crystal frequency: 40 MHz
Flash size:        4MB
Features:          WiFi, BT, Dual Core, 240MHz, VRef calibration in efuse, Coding Scheme None
MAC address:       $MAC
App/part. size:    568,656/4,128,768 bytes, 13.77%
[00:00:00] [========================================]      17/17      0x1000   Skipped! (checksum matches)                                                                                                        [00:00:00] [========================================]       1/1       0x8000   Skipped! (checksum matches)                                                                                                        [00:00:00] [========================================]     271/271     0x10000  Skipped! (checksum matches)                                                                                                        [2025-08-24T10:12:15Z INFO ] Flashing has completed!
Commands:
    CTRL+R    Reset chip
    CTRL+C    Exit

[lenzfilipski]

I have the same error with espflash, also on arch linux.
Using @sirhcel 's fix did resolve the issue.
However, I had to migrate esp-hal from 0.23.1 to 1.0.0-rc1 on my project.