proxmark3/doc/md/PM5_Controllers/PM5_Button_Controller_RM.md

Button Controller Technical Manual

This document is intended for product users and integrators. It describes the button actions, timing parameters, and related business logic of this chip.

• Author: DXL
• Document version: v1.0
• Date: 2026-08-24

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Table of Contents

1. Overview
2. External Signals and Key Actions
3. Button Actions and Timing
4. Effects of Various Conditions on Button Business Logic
5. Detailed Flowcharts
6. Typical Operation Scenarios
7. FAQ and Notes
8. Appendix

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1. Overview

This chip is used to assist the host MCU. It is primarily responsible for:

• Reset control: resetting (rebooting) the host MCU under specific conditions;
• ISP mode management: guiding the host MCU into or out of ISP (In-System Programming) mode through operations such as long presses, for firmware updates;
• Factory test mode: detecting the factory test signal at power-on and guiding the host MCU into a programming state, for production-line flashing.

Terminology

• Host MCU: the target chip managed by this chip, which runs the main application firmware.
• ISP (In-System Programming): in-system programming, used to update the host MCU firmware.

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2. External Signals and Key Actions

2.1 External Signals

Signal	Direction	Meaning	Active Level
BTN_IN	Input	Physical button	High = pressed, Low = not pressed
USB_VBUS	Input	USB connection / power detection	High = USB connected, Low = not connected
MCU_RST	Output	Host MCU reset control	Low = reset, High = normal operation
MCU_BOOT0	Output	Host MCU boot mode selection	High = programming (ISP) mode, Low = normal operation

2.2 Key Actions

Action	Behavior
Reset host MCU	Pull MCU_RST low, hold for about 5ms, then release (pull high), causing the host MCU to restart
Exit ISP	Stop the auto-exit timer → end the ISP state → pull MCU_BOOT0 low → reset the host MCU

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3. Button Actions and Timing

3.1 Three Core Actions

Scenario	Trigger Condition	Result
① Long press to enter ISP / reset (non-ISP mode)	Long press exceeding 6 seconds	See the "USB connected?" branch below
② Long press to exit ISP (ISP mode)	Long press exceeding 3 seconds	Exit ISP, host MCU resets back to normal operation
③ Idle auto-exit ISP (ISP mode)	No button operation for more than 5 minutes	Automatically exit ISP, host MCU resets

The business logic of this chip currently only handles long-press events, not short-press events.
The timings are estimations and are not entirely accurate; this is caused by the limited precision of this chip's internal oscillator.

3.2 USB Branch of Action ①

When a long press exceeds 6 seconds in non-ISP mode:

• USB connected (USB_VBUS high): first pull MCU_BOOT0 high, then reset the host MCU → the host MCU enters ISP (programming) mode;
• USB not connected (USB_VBUS low): only reset the host MCU (equivalent to a restart), without entering ISP.

3.3 Timing Parameter Summary

Parameter	Value	Meaning
Button debounce	10ms	Duration for stable button-state determination
Timing base	100ms	Minimum timing unit for long-press / idle duration
Non-ISP long-press threshold	6 seconds	Long-press threshold in non-ISP mode
ISP long-press exit threshold	3 seconds	Long-press exit threshold in ISP mode
ISP idle timeout	5 minutes	Idle auto-exit duration in ISP mode

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4. Effects of Various Conditions on Button Business Logic

4.1 Key Conditions Affecting Button Behavior

The final behavior of the button is jointly determined by the following three conditions:

1. Whether the device is currently in ISP mode;
2. Whether USB is connected (USB_VBUS);
3. Which processing stage the button is currently in.

4.2 Decision Table

Non-ISP mode:

Button State	Duration	USB	Action
Long-pressing	Released before reaching 6 seconds	—	Cancelled, no action
Long-pressing	Exceeds 6 seconds	Connected	Enter ISP mode (pull MCU_BOOT0 high, then reset)
Long-pressing	Exceeds 6 seconds	Not connected	Only reset the host MCU

ISP mode:

Button State	Duration	Action
Long-pressing	Exceeds 3 seconds	Exit ISP (pull MCU_BOOT0 low, then reset)
No press	Idle for more than 5 minutes	Automatically exit ISP
Holding	Any	ISP idle timing paused (not counted toward timeout)

4.3 Button Processing Stage State Machine

stateDiagram-v2
    [*] --> Released
    Released --> Pressed : stable press (debounce passed)
    Pressed --> LongPressTriggered : threshold reached (6s or 3s)
    Pressed --> Released : released (before threshold, cancelled)
    LongPressTriggered --> Released : released

4.4 Two Important Details

1. After entering ISP, you must "release and then long-press again" to exit: the long press used to enter ISP has already been marked as "processed" for that press. Therefore, to exit ISP via long press, you must first release the button, and then long-press again for 3 seconds.

2. Starting point of the 5-minute idle timeout: when entering ISP, the idle timing is cleared, but it only accumulates while the button is in the "released" state. Therefore, the 5-minute timeout actually begins counting from the moment the button is released after entering ISP; while the button is held, the timeout timing is paused.

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5. Detailed Flowcharts

5.1 Overall Power-on Flow

flowchart TD
    A([Power-on startup]) --> B[Power-on initialization]
    B --> C{Factory test mode detection}
    C -->|Reset signal pulled low within 10ms after power-on, and held for more than 100ms| D[Enter factory ISP mode]
    D --> E{USB disconnected?}
    E -->|No| E
    E -->|Yes| F[Exit ISP, reset host MCU]
    F --> G[Enter operating-mode main loop]
    C -->|No| G

5.2 Factory Test Mode Detection Flow

flowchart TD
    S([Start detection]) --> A[Begin monitoring the reset signal]
    A --> B{Within 10ms of power-on<br>was the reset signal pulled low?}
    B -->|No, held high within 10ms| R1[Do not enter factory mode, return]
    B -->|Yes| C{Reset signal held low<br>for more than 100ms?}
    C -->|No, recovered high early| R2[Do not enter factory mode, return]
    C -->|Yes| D[Wait for reset signal to release high]
    D --> E[Wait another 100ms]
    E --> F[Pull boot mode signal high, reset host MCU<br>enter ISP programming mode]
    F --> G{USB disconnected?}
    G -->|No| G
    G -->|Yes| H[Pull boot mode signal low, reset host MCU]
    H --> I([Return, enter operating mode])

5.3 Operating-mode Main Loop Flow

flowchart TD
    L([Loop start]) --> RD[Read button level]
    RD --> DB[Delay 10ms debounce]
    DB --> P{Button stably pressed?}
    P -->|Yes| S0{First press<br>and long-press timing not started?}
    S0 -->|Yes| S1[Enter long-press detection<br>clear button timing and start timing]
    S0 -->|No| REL
    S1 --> REL
    P -->|No| REL{Button stably released?}
    REL -->|Yes, and a prior button processing exists| RA[Stop timing when not in ISP<br>clear button timing<br>reset button processing stage]
    RA --> L1
    REL -->|No| L1
    L1{Not in ISP and long-press timing exceeds 6 seconds?}
    L1 -->|Yes| S2[Mark this long press as processed<br>stop timing]
    S2 --> USB{USB connected?}
    USB -->|Yes| EI[Pull boot mode signal high<br>enter ISP mode]
    EI --> RST[Reset host MCU]
    USB -->|No| RST
    RST --> RT{Entered ISP mode?}
    RT -->|Yes| TO[Clear idle timing<br>start idle timeout timing]
    RT -->|No| L2
    TO --> L2
    L1 -->|No| L2
    L2{In ISP and long-press timing exceeds 3 seconds?}
    L2 -->|Yes| X[Mark this long press as processed<br>exit ISP]
    X --> L3
    L2 -->|No| L3
    L3{In ISP and no button press<br>and idle timing exceeds 5 minutes?}
    L3 -->|Yes| X2[Exit ISP]
    X2 --> L
    L3 -->|No| L

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6. Typical Operation Scenarios

6.1 Enter ISP to Flash Firmware

1. Confirm that USB is connected (USB_VBUS high);
2. Long-press the button for more than 6 seconds;
3. The host MCU is reset and enters ISP (programming) mode, at which point firmware can be flashed via the host PC.

6.2 Exit ISP and Return to Normal Operation

• Manual exit: first release the button, then long-press again for more than 3 seconds;
• Automatic exit: keep 5 minutes without button operation, and ISP is exited automatically.

6.3 Manually Restart the Host MCU

• Without USB connected, long-press the button for more than 6 seconds; the host MCU will be reset (restarted) without entering ISP.

6.4 Production-line Flashing (Factory Test Mode)

• Within 10ms after power-on, pull the host MCU reset line low and hold it for more than 100ms;
• This chip and the host MCU enter factory ISP mode and remain there until USB is disconnected, after which the host MCU is automatically reset back to normal operation mode.

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7. FAQ and Notes

Question	Explanation
No ISP entry after a long press?	Confirm whether USB is connected; without a connection, a long press only restarts the host MCU.
Once in ISP, a continuous long press cannot exit?	You must first release the button, then long-press again for 3 seconds (the long press that entered ISP does not re-trigger the exit).
How is the long-press time calculated?	Timing starts from when the button is stably recognized as pressed, and is cleared if released midway.
Does ISP exit automatically?	Yes. If there is no button operation within 5 minutes after entering ISP, it exits and resets automatically.
The timing seems inaccurate?	That is expected, because this chip's internal oscillator is not highly precise and may have errors.

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Appendix

Appendix A: Timing Parameter Summary

Parameter	Value	Description
Debounce time	10ms	Stable determination of button state
Non-ISP long-press threshold	6 seconds	Triggers reset or ISP entry when exceeded
ISP long-press exit threshold	3 seconds	Exits ISP when exceeded
ISP idle timeout	5 minutes	Auto-exit ISP with no button operation
Reset pulse width	About 5ms	Low-level time required to reset the host MCU

Note: the times described above are not highly precise.

Appendix B: Glossary

Term	Meaning
This chip	The button controller chip, the subject of this manual
Host MCU	The target chip managed by this chip, which runs the main application firmware
ISP	In-System Programming, used to update the host firmware
Long press	A button held down continuously beyond the configured threshold