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diff --git a/chromium/docs/website/site/chromium-os/chromiumos-design-docs/keyboard-controlled-reset-circuit/index.md b/chromium/docs/website/site/chromium-os/chromiumos-design-docs/keyboard-controlled-reset-circuit/index.md deleted file mode 100644 index c1bac48c696..00000000000 --- a/chromium/docs/website/site/chromium-os/chromiumos-design-docs/keyboard-controlled-reset-circuit/index.md +++ /dev/null @@ -1,83 +0,0 @@ ---- -breadcrumbs: -- - /chromium-os - - Chromium OS -- - /chromium-os/chromiumos-design-docs - - Design Documents -page_name: keyboard-controlled-reset-circuit -title: Keyboard-Controlled Reset Circuit ---- - -To enable users to securely reset a Chrome device, or enter recovery and -developer modes, a hardware circuit is required. This function can be -implemented with a Silego chip, or an equivalent combination of parts and logic. - -### When a user presses a combination of the power key and certain other keys, the hardware circuit monitoring the keyboard generates a reset signal to the embedded controller. The embedded controller controls power to the rest of the system, which is reset as well. The circuit contains a flip-flop that is can only be cleared by the reset signal. This flip-flop is set by a GPIO signal from the embedded controller that is sent before the embedded controller transitions from its read-only firmware to its rewriteable firmware. The output of the flip-flop goes to a GPIO on the main processor, which can use this signal to verify that the EC has been reset and is still running read-only (and hence trusted) code. - -### Reset - -### To reset the system, the user presses Power+F3 (Power+VolumeUp on convertible devices without a secure keyboard connection). When the embedded controller resets, it progresses from read-only firmware to rewritable firmware for operation in Normal Mode. - -### Recovery mode - -To enter Recovery Mode, the user holds Power+F3+ESC (Power+VolumeUp+VolumeDown -on convertible devices without a secure keyboard connection). -When the embedded controller resets in Recovery Mode, it remains in its -read-only firmware and tells the main processor to boot in Recovery Mode. - -### Developer mode - -Users can enter Developer Mode from Recovery Mode, usually by pressing Ctrl+D at -the recovery screen. Developer Mode can be accessed if and only if the flip-flop -indicates that the embedded controller is still in read-only mode. This -requirement ensures that the Recovery Mode firmware on the main processor can -trust the keyboard messages from the embedded controller (and thus ensures that -the keyboard messages are in fact sent by a physical user who is present at the -keyboard—not, for example, from a keyboard that has been hijacked by a remote -process). - -### Optional battery cutoff - -Systems with non-removable batteries may implement a battery cut-off. The -battery can be cut off by removing the power adapter while holding Power+F3 -(Power+VolumeUp on convertible devices without a secure keyboard connection) for -10 seconds or more. The preferred implementation is with a control wire into the -controller/gas-gauge inside the battery pack, but an alternative is to force off -FETs in the charger circuit. This requirement allows users under direction from -support staff to completely cut off power to the device. It also enables users -to recover from situations where the power supply has locked up. For example, an -out of specification USB device causing the main power regulator to latch a -fault and shutdown until power is cycled. - -[<img alt="image" -src="/chromium-os/chromiumos-design-docs/keyboard-controlled-reset-circuit/KbdReset.png">](/chromium-os/chromiumos-design-docs/keyboard-controlled-reset-circuit/KbdReset.png) - -<img alt="KeyboardControlledReset.png.1353360421277.png" -src="https://lh5.googleusercontent.com/fmWa009HCo9PNdjbjeK5rpUVqax0sbm4RMc0bZpvQOM1NmhXZN867EuEZOCAWm8FMHGsIEm7ryT9kB1TITIfIvMyV32fxxw4nX9teXVWJUQ08EL5-vpybhQ9_ZMr74c55g" -height=437px; width=661px;> - -This hardware circuit does the following: - -* When the Power button is pressed, it checks the keyboard matrix to - determine whether F3 or VolumeUp (on convertible devices without a - secure keyboard connection) is also pressed. If so, it causes a - hard-reset of the embedded controller. This action has the side - effect of resetting the entire system. -* It provides an EC_IN_RW indicator for whether the embedded - controller code has transitioned from read-only code to rewritable - code as part of verified boot. This indicator is set by the embedded - controller via the EC_ENTERING_RW GPIO and is reset whenever a hard - reset is triggered. EC_IN_RW should go to a PCH/SOC GPIO line that - can be read by the main processor. EC_IN_RW is an open drain signal - and needs to connect to a pin with an internal pullup or have a - pullup on the board. -* EC_RST_L resets the embedded controller (and the rest of the - system). This is an open drain signal and should be pulled up to the - appropriate power rail. - -The embedded controller boots into read-only (RO) code. It then normally -verifies and jumps to rewritable (RW) code. Before jumping to RW code, the RO -code must assert the EC_ENTERING_RW GPIO. This will set the flip-flop, so that -it asserts the EC_IN_RW signal to the main processor. -Once the flip-flop has been set, it can only be cleared by pressing the Reset -key combination. No action by the embedded controller can clear the flip-flop.
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