Bootrom Error Wait For Get Please Check Stb Uart Receive ((hot)) Full

The "BootROM error wait for get please check stb uart receive full" message indicates a communication failure, often caused by incorrect drivers, swapped TX/RX wires, or improper power sequencing during STB flashing. Solutions include verifying COM port settings, ensuring 3.3V TTL levels, and initiating the software download immediately before powering on the device. Read the full guide at LemmyMorgan

How to dead Gsky V8 revival with a computer using rs232 cable

The error "bootrom error wait for get please check stb uart receive full" typically appears during a Set-Top Box (STB) firmware recovery or "de-bricking" process. It indicates that the device's BootROM is waiting for a "Get" command or data handshake from your PC, but the communication channel (UART) is blocked or misconfigured. Common Causes

Buffer Overflow: The STB’s internal UART receive buffer is full, often because the PC is sending data faster than the device can process it or without waiting for the required handshake.

Physical Connection Faults: Loose RX/TX wires, missing common ground (GND), or swapped RX/TX pins.

Voltage Mismatch: Using a 5V TTL adapter on a 3.3V logic board (or vice versa), which can cause signal noise and data corruption.

Incorrect Serial Settings: Mismatched baud rates or incorrect parity/stop bit settings preventing clear communication. Step-by-Step Recovery Guide Verify Hardware Interface

Pins: Double-check that your USB-to-TTL adapter’s TX goes to the STB's RX, and RX to TX.

Ground: Ensure a solid GND connection between the adapter and the STB board.

Voltage: Set your adapter to 3.3V (most common for STBs) unless the board specifically requires 5V. Adjust Software Tool Settings

Baud Rate: Ensure the tool (e.g., GXDownloader_boot.exe or similar) is set to the correct speed, typically 115200 or 9600.

COM Port: Verify that you have selected the correct port assigned to your adapter in Windows Device Manager. Perform the "Cold Start" Sequence

Press Start in your upgrade tool before powering on the STB.

Once the tool displays "Wait," plug in or switch on the STB power.

If it fails, try the "button-trick": hold the Power or U-BOOT button on the device while plugging it in to force it into the correct boot mode. Hardware Loopback Test (If still failing) Disconnect the adapter from the STB.

Bridge the TX and RX pins on the adapter itself using a jumper.

Open a terminal (like Putty) and type; if the characters appear on the screen (echo), the adapter and drivers are working correctly. If you'd like, let me know: The exact model of your set-top box.

The upgrade tool you are using (e.g., GXDownloader, Putty, Hitool).

Whether the box is completely dead (no lights) or stuck on a logo/boot loop.

The error message "bootrom error wait for get please check stb uart receive full" is a critical failure typically encountered during the firmware flashing or unbricking process of digital satellite receivers (STBs), such as those using National Chip (GX) or Montage chipsets. It indicates a communication breakdown where the Set-Top Box (STB) is unable to process incoming data from your computer via the serial (UART) interface. Understanding the Error

When you see this message, the bootloader (BootROM) on your STB is stuck waiting for a "GET" request—a signal to begin receiving the firmware file—but finds its internal UART buffer "full" or unresponsive. This prevents the flashing software, such as GXDownloader_boot, from initiating the data transfer. Common Causes

Incorrect Cable Wiring: Using a standard serial cable instead of a "cross-line" (Null Modem) cable, where the TX and RX pins must be swapped.

Baud Rate Mismatch: The communication speed (e.g., 115200) between the PC and the STB is not synchronized, leading to buffer overflows.

Driver Issues: The USB-to-RS232 adapter driver is either outdated or incorrectly installed on your PC.

Power Sequencing: The device was not powered on at the exact moment the software requested the "ROM request".

Hardware Interference: Other external connections or a lack of a common ground (GND) between the adapter and the STB can cause signal noise. Step-by-Step Troubleshooting Guide Verify the Hardware Connection

Ensure you are using a cross-line cable (TX to RX, RX to TX).

Check for a common ground; the GND pin of your USB-UART adapter must be securely connected to the STB's GND.

If using an adapter, confirm it is set to 3.3V TTL logic levels rather than 5V, as most STBs operate on 3.3V. Configure Flashing Software Correctly

Chip Type: Set this accurately (e.g., "Others" or your specific chipset model like GX3211).

Serial Port: Double-check that you have selected the correct COM port in Device Manager.

Mode: Ensure it is set to "serialdown" for firmware recovery. Master the Power-On Timing

The most frequent fix for "wait for get" is timing. Click "Start" in your downloader tool before plugging in or switching on the STB.

The tool must be in its "Waiting..." state when the STB boots to intercept the BootROM signal correctly. Check for Buffer/Driver Errors

If the "Receive Full" error persists, try lowering the Baud Rate to 9600 to see if communication stabilizes, then gradually increase it.

Reinstall your PL2303 or CH340 drivers to ensure the PC can handle the data stream without stalling. Clean the Flash (Last Resort)

If you can establish a brief connection before the error, use the tool to perform a "Full Erase" of the flash memory before attempting to write the new firmware.

Are you using a specific downloader tool like GXDownloader or MTK Flash, and do you have a multimeter to check your cable's continuity?

This error typically occurs when trying to flash or recover a set-top box (STB) or microcontroller (like those using the GX6605S chip) using a computer and a serial cable It indicates that the is waiting for a response, but the communication via the (serial) port is failing or the buffer is full The Story: The Message in the Bottle

Imagine your STB is a lonely island and your computer is the mainland. To fix the island's broken bridge (the firmware), you need to send a message in a bottle (the boot file).

: You throw the bottle into the sea. Your computer screen says, "Wait for get" The "BootROM error wait for get please check

. It’s looking for a signal from the island that it's ready to talk. The Silence

: You restart the island (power on the STB), but the computer keeps shouting, "Please check STB UART receive full"

. This means the island's "mailbox" is clogged, or the wires connecting the island to the mainland are crossed.

: You check your "shipping lines" (the RS232 or USB-to-TTL cable). You realize the TX (Transmit) RX (Receive)

wires are swapped, or the ground wire is loose. Once you swap them back and restart the power at just the right moment, the island finally sees the message, and the "bridge" begins to rebuild. Practical Troubleshooting Steps If you are seeing this error, try these fixes: Check Wiring : Ensure your is connected to the STB's to the STB's . A common mistake is connecting TX to TX. Verify Voltage

: Ensure your USB-to-UART adapter is set to the correct voltage (usually Correct COM Port : Verify in Windows Device Manager

that you have selected the correct COM port in your flashing tool (e.g., GXDownloader The "Power Trick" : Many tools require you to click "Start" first, and

plug in or power on the STB so the BootROM can catch the initial "handshake" signal. , such as the GX6605S or STM32?

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This error typically appears when a Set-Top Box (STB)—often based on Guoxin (GX) or similar chipsets—fails to establish a handshake with a PC during a firmware flash or recovery process. It indicates that the STB's BootROM is waiting for a "Get" command from the upgrade tool, but the UART communication buffer is either overwhelmed or physically disconnected. Understanding the Error Components

"BootROM error wait for get": The device has entered its low-level boot mode and is waiting for the PC software to send the initial command (0x7F or similar) to start the transfer.

"Please check STB UART receive full": The STB’s internal UART receive buffer is full, likely because data was sent too fast, at the wrong baud rate, or the hardware handshake failed. Recommended Troubleshooting Steps Check Physical Connections

Cross-Link Wiring: Ensure your RS232 or USB-to-TTL adapter is wired correctly: TX to RX and RX to TX.

Common Ground: Confirm the GND pin of your adapter is connected to the GND pin on the STB board.

Voltage Levels: Most STBs use 3.3V TTL. Ensure your adapter is not set to 5V, which can cause communication errors or damage. Verify Software Configuration

Baud Rate: The standard for most STB recovery tools (like GXDownloader) is 115200, but some older chips may require 9600 or 57600.

Serial Port Settings: Use 8 data bits, 1 stop bit, and No parity (8N1) unless the specific guide for your box says otherwise. Execute the "Power Cycle" Trick

Firmware tools often require you to click "Start" in the software before plugging in the STB power. Step-by-step: Close the tool →right arrow Unplug the STB →right arrow Click "Start" in the tool →right arrow

Plug in the STB power. This allows the tool to catch the very first "Request" from the BootROM. Hardware Handshaking (Flow Control)

If the tool reports the buffer is "full," try disabling all flow control (RTS/DTR) in your device manager settings, as many simple 3-pin UART headers on STBs do not support it. Common Recovery Tools

If you are working with Guoxin-based boxes (e.g., Gsky, Tiger, or Starsat), you may need specific versions of GXDownloader_boot or similar vendor-specific utilities.

Do you have the specific model number of your Set-Top Box or the name of the flashing tool you are using?

Troubleshooting the "Bootrom Error: Wait for Get, Please Check STB UART Receive Full"

If you are trying to flash a firmware update or unbrick a digital set-top box (STB) and you've encountered the cryptic message "Bootrom error: wait for get please check stb uart receive full," you’re likely dealing with a communication breakdown between your PC and the device's processor.

This error is most common in devices using Montage, Ali, or NationalChip chipsets. It essentially means the computer is sending data, but the STB's hardware buffer is overflowing or not acknowledging the handshake.

Here is a comprehensive guide to understanding why this happens and how to fix it. What Does This Error Actually Mean?

To understand the fix, you need to understand the "conversation" happening:

Wait for Get: The computer (via the flashing tool) is waiting for a "Ready" signal from the STB.

UART Receive Full: The Universal Asynchronous Receiver-Transmitter (UART) is the hardware component responsible for serial communication. "Receive Full" indicates that the STB's data buffer is jammed. It cannot process the incoming bits fast enough, or the data is arriving "corrupted," causing the buffer to hang. Primary Causes

Incorrect Baud Rate: The "speed" of the data transfer doesn't match between the software and the hardware.

Poor Physical Connection: Loose TX/RX wires or a faulty RS232-to-USB adapter.

Power Sequencing: The STB wasn't powered on at the exact moment the software expected it.

Driver Incompatibility: Using an outdated or incorrect Prolific/CH340 driver for your USB-to-Serial cable. Step-by-Step Solutions 1. Check Your Wiring (The "TX/RX" Swap)

The most common hardware mistake is the wiring. In serial communication:

TX (Transmit) on your adapter must go to RX (Receive) on the STB.

RX (Receive) on your adapter must go to TX (Transmit) on the STB. GND (Ground) must be connected to GND.

If you have TX to TX, the STB will never "receive" the command, leading to a timeout or a buffer error. Try swapping the TX and RX pins to see if the error clears. 2. Adjust the Baud Rate

Flashing tools (like the Montage "Upgrade.exe" or GX6605S Downloader) usually default to 115200. However, some older boards or specific recovery modes require a slower speed to prevent the "Receive Full" error. Go to Device Manager > Ports (COM & LPT). Right-click your Serial Port > Properties > Port Settings.

Try lowering the Bits per second to 9600 or 57600, and match this setting inside your flashing software. 3. The "Power Cycle" Timing

Bootrom errors often occur because the STB is already in a "frozen" state when the software tries to talk to it. Turn the STB OFF (unplug the power). In the PC software, click "Start" or "Connect" first. Verify Power Supply : Ensure that the power

Only then plug in the power to the STB.The software needs to catch the "Bootroom" signal the millisecond the chip receives power. 4. Use a Different USB-to-TTL Adapter

Cheap RS232-to-USB adapters (especially those using "fake" Prolific chips) often have timing issues that cause the STB buffer to overflow. If possible, switch to an adapter using the CP2102 or FTDI chipset, as they handle high-speed serial data much more reliably. 5. Disable "FIFO" Buffers in Windows

Windows tries to manage serial data by buffering it, which can interfere with the STB's simple Bootrom logic. In Device Manager, go to your COM port Properties. Click Advanced.

Uncheck "Use FIFO buffers" (or slide both bars to the far left/lowest setting). Restart the software and try again. Summary for Specific Chips

Montage Chips (CS6001/CS8001): Often require the "Receive Full" fix by using a 4-pin header instead of the standard RS232 port.

GX6605S: Highly sensitive to the quality of the GND (Ground) wire. Ensure your ground is solid, or the data will be "noisy," filling the buffer with junk.

By methodically checking the timing of the power-on and the integrity of the TX/RX crossover, you can usually bypass this error and proceed with your firmware flash.

Are you using a USB-to-TTL adapter or a standard RS232 cable for this connection?

Troubleshooting BootROM Errors: Waiting for GET and STB UART Receive Full

If you're experiencing BootROM errors, particularly when waiting for a GET request or encountering a situation where the STB (Set-Top Box) UART receive buffer is full, follow these steps to troubleshoot and potentially resolve the issue:

Step 4: Perform Hardware Checks

  1. Verify Power Supply: Ensure that the power supply is stable and within the recommended voltage range.
  2. Check for Loose Connections: Verify that all connections, including UART and STB connections, are secure and not loose.
  3. Perform a System Reset: Try performing a system reset or power cycle to see if the error persists.

Advanced Troubleshooting Techniques

If the above steps do not resolve the issue, you may need to use more advanced troubleshooting techniques, such as:

  1. Using a Debugger: Use a debugger to step through the BootROM code and identify the exact cause of the error.
  2. UART Sniffing: Use a UART sniffer to monitor the UART communication and analyze the data being transmitted and received.
  3. System Logging: Enable system logging to capture any error messages or debug information that may help identify the cause of the error.

Conclusion

The "Wait for Get, Please Check STB UART Receive Full" error can be a challenging issue to resolve, but by following the step-by-step troubleshooting guide outlined in this article, you should be able to identify and fix the underlying cause of the error. Remember to methodically check each component of the system, including UART communication, firmware or software, STB configuration, and hardware connections. If you're still experiencing issues, don't hesitate to seek additional help from the relevant technical support teams or online communities.

The error message "BOOTROM error wait for get please check STB UART receive full" typically occurs during the serial flashing or "unbricking" process of a Set-Top Box (STB). It indicates a communication breakdown between the recovery tool on your PC and the STB's hardware bootloader. Core Meaning of the Error

Wait for Get: The STB’s BootROM is in a listening state, waiting for a "Get" command (often 0x7F in STMicroelectronics protocols) from the flashing software to initiate data transfer.

UART Receive Full: The serial buffer on the STB side has filled up with data it cannot process, or the handshake between the PC and the STB failed to clear the buffer. This usually stops the flashing process immediately. Common Causes

Incorrect Boot Files: Using a bootloader file (.boot or .bin) that does not match the specific chip version (e.g., GX3211 vs. GX6605).

Cable Issues: A faulty RS232-to-USB adapter, incorrect wiring (TX/RX swapped), or a missing Ground (GND) connection.

Driver Mismatch: The RS232 cable driver is either missing or incorrectly configured in Windows Device Manager.

Interference: Anti-virus software or other background serial monitors (like an open terminal emulator) might be intercepting the data. Troubleshooting Steps

Verify Connections: Ensure the TX, RX, and GND pins are securely connected. Note that some STB recovery processes require a "cross-line" (Null Modem) configuration where PC-TX goes to STB-RX and vice versa.

Power Timing: Most recovery tools (like GXDownloader) require you to click Start while the STB is powered OFF, and then plug in the STB power immediately after.

Check Port Settings: Match the COM port settings in your software to the STB's requirements (commonly 115200 baud rate, 8 Data bits, None Parity, 1 Stop bit).

Hardware Reset: If the "UART receive full" error persists, try a "hard reset" by holding the reset button on the STB (if available) while powering it on to force it into BootROM mode.

This error typically occurs when a Set-Top Box (STB) upgrade tool (like GXDownloader

) is waiting for a "handshake" or response from the device's BootROM via the serial interface, but the communication is failing

. It often means the tool cannot establish a connection to start the data transfer. Top Troubleshooting Steps Check Physical Connections & Power Cycle Power Timing : Click "Start" on the upgrade tool

, and then power on or restart your STB. The tool needs to be in its "waiting" state when the box triggers its boot process. GND Connection : Ensure the Ground (GND)

wire is securely connected between your USB-to-UART adapter and the STB's UART pins. RX/TX Swap : Verify that your (Transmit) pin on the adapter is connected to the (Receive) pin on the STB, and vice versa. Verify Serial Settings & Hardware Voltage Level : Most STBs use

. Check that your adapter is set to 3.3V rather than 5V to avoid communication errors or hardware damage. Driver & Port : Confirm that the RS232/UART driver

is correctly installed on your PC and that you have selected the correct in the tool. Cable Type

: Ensure you are using a proper serial cable; some setups require a cross-over (null modem) configuration. Software Configuration (GXDownloader Example)

: Ensure you have selected the correct chip model (e.g., "Others" or a specific GX chip). : Double-check that you have selected the correct file for your specific STB hardware. USB Interference

: Disconnect other unnecessary USB devices from your PC to prevent interference with the serial signal. STMicroelectronics Community Alternative Fix: USB Recovery

If UART flashing continues to fail, many modern STBs support a "blind" USB recovery: Rename your firmware file to and place it on a FAT32 formatted USB drive Insert it into the STB and hold the button on the front panel while powering the device on. Are you using a specific upgrade tool like GXDownloader , and have you already tried swapping the RX and TX

The error message "bootrom error wait for get please check stb uart receive full" typically indicates a communication failure between your computer and a Set-Top Box (STB) or microcontroller during a firmware flashing process. It means the system is stuck waiting for a response ("get") but the data buffer is full or the connection is blocked. Common Fixes Check Hardware Connections: Ensure the TX and RX lines are not swapped.

Verify the GND (Ground) connection between your USB-to-UART adapter and the board.

Ensure the voltage levels match (e.g., 3.3V vs 5V) to avoid interference or hardware damage.

Verify Boot Mode: Ensure the device is correctly set to "Bootloader Mode" (often by holding a specific button or setting a jumper like BOOT0) before starting the transfer. Advanced Troubleshooting Techniques If the above steps do

Adjust Baud Rate: If the receive buffer is "full" or getting garbage data, try lowering the baud rate (e.g., from 115200 to 9600) in your flashing software to stabilize the connection.

Power Cycle: Disconnect and reconnect the power to both the device and the UART adapter. Sometimes other active connections (like a plugged-in USB cable) can interfere with the serial bootloader.

Clear Port Interference: Close any other programs (like Serial Monitors or Putty) that might be trying to use the same COM port.

Here’s a piece of technical documentation / debug log written in the style of an engineer’s field report, based on the error you described.

Step 6: Check for BootROM Key Sequence

Research your specific chip/board (e.g., HiSilicon, Amlogic, Broadcom, MStar).
Common boot interrupt keys:

Without the correct key, the bootloader proceeds to normal boot and ignores UART commands, causing the "wait for get" timeout.

B. Flow Control Absence (Hardware or Software)

Most STB UARTs use only TX, RX, and GND. No CTS/RTS hardware flow control. If your PC sends data before the STB is ready, the small UART FIFO (often only 16 to 64 bytes) overflows. The error receive full indicates the device has no backpressure mechanism.

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This error typically occurs when you're trying to flash or recover a set-top box (STB) or similar embedded device using a serial (UART) connection. It essentially means the device's BootROM (the permanent, read-only code that starts the system) is waiting for data but its input buffer is full because it can't process the incoming signals correctly. 🧩 What the Error Actually Means

"Wait for Get": The BootROM is stuck in a loop, waiting to "get" a valid command or handshake signal from your computer.

"UART Receive Full": The internal hardware buffer for serial data is full. This usually happens when the data being sent doesn't match the expected format (like the wrong baud rate), causing "garbage" characters to pile up until there's no more room. 🛠️ The "Detailed Story" of Why This Happens

This isn't usually a hardware failure, but a misalignment between your PC and the box. Here are the most common culprits: 1. Baud Rate Mismatch (The #1 Cause)

The BootROM expects data at a very specific speed (often 115200, 9600, or sometimes a strange one like 74880 for certain chips). If your PC is sending at 115200 and the box is listening at 9600, the data becomes unreadable "noise" that fills up the buffer without triggering a successful "get". 2. Faulty RX/TX Wiring

Crossed Wires: Ensure your USB-to-UART adapter’s TX (Transmit) is connected to the box’s RX (Receive), and vice versa.

Loose Ground: If the GND (Ground) wire is loose, the signal becomes unstable, leading to erratic data that floods the UART buffer. 3. Power-On Timing

Many STB recovery tools require you to click "Start" or "Connect" on your PC before you plug in the power to the box. If you power it on too late (or too early), the BootROM might miss the initial handshake and enter an error state where it just reports the buffer is full. 4. Driver/Port Issues

Virtual Machines: If you're using a VM, the USB-to-Serial passthrough often fails or lags, causing data overflows.

CH340/PL2303 Drivers: Ensure your USB-to-UART adapter drivers are updated. Cheap "clone" chips often have stability issues with BootROM-level communication. ✅ How to Fix It

Check your Speed: Try the most common baud rates in your software: 115200, 57600, or 9600.

Verify Voltage: Most STBs use 3.3V TTL. If your adapter is set to 5V, it can cause data corruption or even damage the pins. The "Hard Reset" Method: Unplug the STB power. Open your flashing tool (like GxDownloader or Hitool). Select the correct COM port and click "Connect/Start". Then plug in the power.

Shorten the Cables: Long, unshielded serial wires pick up interference from power supplies, which the BootROM interprets as incoming data, filling the buffer.

If you're still stuck, let me know the model of the STB or the chipset (like HiSilicon, Montage, or ALi) and I can give you the exact settings for that hardware.

The error message "bootrom error wait for get please check stb uart receive full" is a low-level diagnostic signal frequently encountered by developers and hobbyists working with embedded systems, specifically Set-Top Boxes (STBs). It signifies a communication breakdown during the earliest stage of the device’s boot process. The Mechanics of the Bootrom Phase

The BootROM is a tiny, read-only memory chip containing the first code a processor executes upon power-up. Its primary job is to initialize basic hardware and locate the secondary bootloader (like U-Boot) on the device's storage. When the BootROM is configured to "wait for get," it is essentially sitting in a listening mode, expecting a command or a data packet via the UART (Universal Asynchronous Receiver-Transmitter) serial interface. Deciphering the Error

The specific phrase "stb uart receive full" indicates a buffer overflow. In technical terms, the STB has received more data than its small hardware buffer can process, or the data it received was malformed/noisy, causing the system to "hang" while waiting for a valid instruction. This usually happens for three reasons:

Baud Rate Mismatch: The most common culprit. If your PC is sending data at 115,200 bits per second but the STB is expecting 9,600, the data becomes unintelligible "noise" that fills the buffer with garbage.

Hardware Connection Issues: Poorly shielded serial cables or loose Ground (GND) wires can introduce electromagnetic interference. This interference is interpreted by the BootROM as incoming data, quickly filling the receive register.

Incorrect Boot Mode: The device might be forced into a "recovery" or "factory flash" mode via a physical jumper or button. In this state, the BootROM refuses to load the OS and waits indefinitely for a new firmware image via UART. Troubleshooting and Resolution

To resolve this, one must first ensure that the serial configuration matches the manufacturer's specifications (typically 115200 baud, 8 data bits, no parity, 1 stop bit). Physical inspections of the TTL adapter and wiring are also essential to rule out "ghost" signals. If the hardware is sound, the error usually implies the device is "bricked" or has a corrupted flash memory, requiring a forced firmware re-flash using specialized tools like Hitool or Putty.

Ultimately, this error is a gateway into the "heart" of the machine. While frustrating, it confirms that the processor is alive and capable of communication, providing a starting point for recovery rather than indicating a total hardware failure.

Here’s a concise post you can use for a forum, support ticket, or internal log regarding the BootROM error you’re seeing:

Title: BootROM Error: “wait for get” / UART receive full – STB stuck at boot

Issue:
Device stops during boot with the following UART console output:

BootROM error
wait for get
please check stb uart receive full

Environment:

Observed behavior:

Probable causes:

  1. UART buffer overflow – Host PC sent data too fast before BootROM was ready.
  2. Incorrect baud rate – Mismatch between BootROM’s expected baud rate (often 115200 or 1152000) and terminal settings.
  3. Corrupted boot image – The image being sent over UART is invalid or incomplete.
  4. Flow control missing – No hardware/software flow control, causing receive FIFO full.
  5. Boot pin strapping – Device not entering proper download mode.

Troubleshooting steps tried:

Need help with:

Step 4: Clear Buffer and Retry

  1. Power off the device.
  2. Close the serial terminal.
  3. Reopen the terminal with correct settings.
  4. Power on the device while immediately sending a break/interrupt key (often Ctrl+C or Enter repeatedly).

Step 2: Shorting the Flash Pins (Hardware Repair)

This is a common technique to force the processor into a mode that accepts a fresh firmware write.

  1. Locate the NAND or SPI Flash chip on the motherboard.
  2. Identify the Data pins (D0-D7).
  3. While powering on the device, briefly short specific data pins (usually Data 0 or Clock pins depending on the chip model) to Ground using a needle or resistor.
  4. This confuses the processor, preventing it from reading the corrupted boot code, and forces it into a "Waiting for Download" state where you can flash a valid firmware via USB or Serial.