docs/servo_v4.md - chromiumos/third_party/hdctools - Git at Google

 # Servo v4

 Servo v4 is a debug device in the Servo family.

 Servo v4 functions as a configurable USB hub to support developer and lab
 recovery features. However, it doesn't have any hardware debug features on its
 own. It must be paired with CCD (GSC's on-board servo implementation) or
 [Servo Micro].

 [TOC]

 ## What is Servo v4?

 Servo v4 combines the functionality of the following devices into one:

 *   Ethernet-USB dongle
 *   Muxable USB port
 *   microSD to USB3.0 dongle
 *   Keyboard emulator
 *   Pass through charger
 *   [Case-Closed Debug (CCD)][CCD] interface ([SuzyQ] debug cable)

 Details:

 *   [Servo v4 Block Diagram]
 *   [Servo v4 Schematic]

 ![Servo v4 with Accessories](images/servo_v4.jpg)

 ## Getting Servo v4

 <!-- mdformat off(b/139308852) -->
 *** promo
 Sorry, Servo v4 is not publicly available for purchase.
 ***
 <!-- mdformat on -->

 <!-- mdformat off(b/139308852) -->
 *** note
 **IMPORTANT**: You will need to [update the firmware](#updating-firmware)
 before using, as the factory firmware is quite old.
 ***
 <!-- mdformat on -->

 ### Partners

 Your contact at Google should be able to provide you with Servo v4.

 ### Googlers

 Stop by your local Chromestop, or use http://go/hwrequest and enter `Servo V4`
 for the `Google Code Name`.

 ## How to Use Servo v4

 The plastic case has labels `HOST`, `DUT POWER`, and `uSERVO`.

 *   `HOST`: Servo v4 can be plugged into a host machine using a micro-B USB
     cable via the micro-B USB port marked `HOST`. This will power Servo v4 while
     allowing the user to control Servo v4 using [`servod`].

 *   `DUT POWER`: USB-C port labeled `DUT POWER` is for powering the DUT through
     the Servo. Servo v4 can be used to power the DUT which becomes useful for
     devices that use USB-C as their only charge port (tablets, phones etc.). The
     Type-C port can be used to plug in any Type-C charger to provide full
     charging capabilities as a charge through hub. If no charger is plugged,
     Servo v4 will act as a passive hub.

 *   `uSERVO`: On the side labeled `uSERVO` there are two connectors.

     *   The DUT connector (which is a captive cable: servo side is permanently
         connected) can be plugged into a DUT, providing the DUT access to the
         ethernet and blue USB port. The Type-C captive cable enables debugging
         of devices that have a GSC (recent Chromebooks) through [CCD].

     *   The "uServo" USB port can be used to plug a servo micro to debug DUT
         over the Yoshi debug header.

 *   The following ports on the unlabeled side can be used to download data to a
     device:

     *   Ethernet
     *   microSD card
     *   USB stick

 Servo v4 has an embedded keyboard so keystrokes can be emulated on the DUT.

 The [`servod`] server must be running for Servo v4 to work. Details can be found
 on the [Servo] page.

 ## Type-A vs Type-C Variants

 There are two variants of Servo V4: Type-A and Type-C.

 Both versions use the same board and case, but have a different captive cable
 stuffed.

 ### Type-C Version

 The Type-C version acts as both a USB hub and PD charger. Servo v4 can also
 control both CC terminations which allows it to act as a debug accessory. It
 should be used on systems with [CCD].

 <!-- mdformat off(b/139308852) -->
 *** note
 NOTE: Type-C Servo v4 is a charge-through hub and is NOT functionally equivalent
 to a Type-A servo with an A-to-C adapter. DO NOT use a Type-C Servo v4 just
 because you want to plug into a Type-C port. Older Chromebooks (Eve, Samus,
 etc.) have [EC] bugs that prevent charge through hubs from working correctly.
 ***
 <!-- mdformat on -->

 ![Servo v4 Type-C](images/servo_v4_typec.jpg)

 ### Type-A Version

 The Type-A version is used with a uServo and serves as the DUT USB hub, with the
 uServo providing SPI and UART support.

 ![Servo v4 Type-A](images/servo_v4_typea.jpg)

 ## Servo v4 Revisions

 Servo v4 had several revisions, indicated by board color. The mass production
 (MP) version is available from Chromestop.

 ### Green (MP)

 Final version, has full functionality.

 ### Blue (DVT)

 The DVT version is completely functional except for the one bug affecting only
 Type-C variant. There are about one thousand of these, so you may encounter
 them.

 *   PD Charge-through only works on chargers up to 10V.
 *   Firmware identifies this by board revision and will not negotiate any
     voltages above 10V.

 ### Red (EVT)

 The EVT version is a mostly functioning version with a few bugs. There are
 around three hundred of these total.

 *   The ethernet IC has a bug in it that makes the device fall out of
     GigE/USB3.0 speeds under certain circumstances and it falls down to USB1.1 /
     2 speeds and never properly recovers until reset.
 *   Type-C variant doesn't function, Type-A works OK.

 ## Software

 Servo v4 runs more or less equivalently to Servo v2, through [`servod`].
 It's intended to be mostly transparent, but there are some differences.

 Most functionality is exported through `dut-control`.

 ```bash
 (HOST) $ start-servod -b <board> -s <serial>
 ```

 To use with a specific board, you can connect a servo_micro to the "uServo"
 labeled port (or use the Type-C cable to connect to [CCD]) and run [`servod`],
 which will load the board config and control both Servo v4 and Servo Micro (or
 GSC).

 ```bash
 (HOST) $ start-servod -b [board] -s [serialno printed on servo v4 sticker]
 ```

 ### Recipes

 #### Connect to Servo_v4 console with Servod

 ```bash
 (HOST) $ minicom -D "$(dut-control -- -o servo_v4_uart_pty)"
 ```

 #### Connect to Servo consoles without servod

 When Servos are plugged in, it creates several console endpoints starting at
 `/dev/ttyUSB0` and incrementing based on the hardware present. If you connect
 to these you can directly interact with the Servo firmware STM32 or DUT shells.
 Not all shells will be active depending on device setup.

 ```bash
 (HOST) $ minicom -D /dev/ttyUSB0
 > version
 Chip:   stm stm32f07x
 Board:  3
 RO:     servo_v4p1_v2.0.24151-03b2123fb
 ```

 #### Switch SD to Host

 ```bash
 (HOST) $ dut-control -- sd_en:on sd_pwr_en:on sd_mux_sel:servo_sees_usbkey host_sd_usb_mux_en:on host_sd_usb_mux_sel:sd
 ```

 #### Switch SD to DUT

 ```bash
 (HOST) $ dut-control -- sd_en:on sd_pwr_en:on sd_mux_sel:dut_sees_usbkey
 ```

 #### Disable SD

 ```bash
 (HOST) $ dut-control -- sd_en:off sd_pwr_en:off
 ```

 #### Switch USB3 to Host

 ```bash
 (HOST) $ dut-control -- usb3_mux_en:on usb3_mux_sel:servo_sees_usbkey usb3_pwr_en:on host_sd_usb_mux_en:on host_sd_usb_mux_sel:usb
 ```

 #### Switch USB3 to DUT

 ```bash
 (HOST) $ dut-control -- usb3_mux_en:on usb3_mux_sel:dut_sees_usbkey usb3_pwr_en:on
 ```

 ### Disable/Enable [SuzyQ] wiring (debug accessory mode)

 <!-- mdformat off(b/139308852) -->
 *** note
 Type-C Servo v4 only
 ***
 <!-- mdformat on -->

 ```bash
 (HOST) $ dut-control -- servo_v4_dts_mode:off [on]
 ```

 #### Connect remotely

 ```bash
 (HOST) $ dut-control -- --host XXX --port YYY
 ```

 ### Disable/Enable Chargethrough

 <!-- mdformat off(b/139308852) -->
 *** note
 Type-C Servo v4 only
 ***
 <!-- mdformat on -->

 ```bash
 (HOST) $ dut-control -- servo_v4_role:snk [src]
 ```

 ## Firmware flashing and reading

 <!-- mdformat off(b/139308852) -->
 *** note
 When flashing the BIOS or EC with [CCD], you need to make sure the [`FlashAP`]
 capability is enabled in GSC.
 ***
 <!-- mdformat on -->

 Read and flash AP firmware (BIOS) with CCD or any other servo debug connection:

 ```bash
 (chroot) $ sudo futility read --servo -v "$OUTFILE"
 (chroot) $ sudo futility update --servo -v -i "$INFILE"
 ```

 ## Updating Firmware {#updating-firmware}

 The latest firmware is available via the servod docker image. You need to have go/servod
 configured. That would also add servo_updater CLI to your host shell.

 <!-- mdformat off(b/139308852) -->
 *** note
 **NOTE**: [`servod`] must not be running. You should have recent versions of
 start-servod and servo_updater scripts that are in hdctools repo (repo sync)

 ***
 <!-- mdformat on -->

 **Update to latest stable firmware:**

 ```bash
 (HOST) $ servo_updater -- -b servo_v4
 ```

 **Rollback to previous stable version if needed:**
 ```bash
 (HOST) $ servo_updater -- -b servo_v4 -c prev --allow-rollback
 ```
 ---
 Advanced usage below:

 - Update to specific binary file

 ```bash
 (HOST) $ servo_updater -f <file_path> -- -b servo_v4
 ```

 - Update to specific FW channel

 ```bash
 (HOST) $ servo_updater -- -b servo_v4 -c [alpha|dev|prev|stable]
 ```

 - If you need to update FW, before it reaches monthly released servod image specify
 channel for servod docker distribution ("release" is default)

 ```bash
 (HOST) $ servo_updater --updater_channel [local|latest|beta|release] -- -c [alpha|dev|prev|stable] -b servo_v4 [...]
 ```

 ## Enabling Case Closed Debug (CCD)

 See [CCD] for complete details.

 <!-- mdformat off(b/139308852) -->
 *** note
 If using a Type-C Servo v4, these commands will only work if the USB-C cable is
 plugged into the correct USB port. Generally, this is the USB port on the left
 side of the device. If the command doesn't work, try the other ports.
 ***
 <!-- mdformat on -->

 Connect to GSC console:

 ```bash
 (HOST) $ minicom -D "$(dut-control -- -o gsc_uart_pty)"
 ```

 Check the GSC FW version in the GSC console:

 ```
 > version
 Build:   0.4.10/cr50_v1.9308_B.269-754117a
 ```

 <!-- mdformat off(b/139308852) -->
 ***note
 CCD requires Cr50 version 0.3.9+ / 0.4.9+
 *   0.4.x is the "pre-pvt" version, for pre-production devices.
 *   0.3.x is the "mp" version, for production devices. This requires the device
     to be in developer mode before "ccd open".
 *   0.0.22 is the factory preflash from GUC. It needs an update.
 ***
 <!-- mdformat on -->

 Open CCD in the GSC console:

 ```
 > ccd open
 ```

 Press power button when prompted. It should take around 5 minutes.

 <!-- mdformat off(b/139308852) -->
 *** note
 If you get an access denied error when attempting `ccd open`, you likely do
 not have developer mode enabled.
 ***
 <!-- mdformat on -->

 <!-- mdformat off(b/139308852) -->
 *** note
 GSC loses the developer mode state after "opening CCD". If your device boots
 into recovery mode, try re-entering developer  mode.
 ***
 <!-- mdformat on -->

 Enable testlab mode in the GSC console:

 ```
 > ccd testlab enable
 ```

 Press power button some more. CTRL+C to exit.

 Run [`servod`] as normal, [CCD] should be enabled now.

 ## Known issues

 *   Displayport - not supported
 *   Type-A/Type-C: Servo V4 comes in two variants on the captive cable, both can
     be obtained from Chromestop.
 *   Type-C Servo is not interchangeable with Type-A. Type-C must be paired with
     CCD, Type-A must be paired with Servo Micro.
 *   DFU: To use util/flash_ec you must enable DFU by connecting servo with an
     A-A cable plugged into an OTG cable. USB ID is tied to BOOT0 indicator on
     the STM32 part.

 ### Interop Problems with Some Switches

 See http://b/112187276.

 Your network switch port will get hosed (some TX buffer fills up and starts
 dropping things) if you have Servo v4 connected to most switches and unplug the
 servo's USB connection, or power off the DUT fully, after the servo's NIC has an
 IP. This behavior is not reproducible with a [GS108Tv2], so the workaround is to
 use a [GS108Tv2].

 [GS108Tv2]: https://www.amazon.com/NETGEAR-Ethernet-Unmanaged-Lifetime-Protection/dp/B003KP8VSK/

 ## Bugs

 File bug or feature requests [here][Bug].

 ## Programming

 <!-- mdformat off(b/139308852) -->
 *** note
 You don't need to do this unless you're developing Servo v4 firmware.
 ***
 <!-- mdformat on -->

 Servo v4 code lives in the [EC] and [`hdctools`] codebase. It can be built as
 follows:

 ```bash
 (chroot) $ cd ~/chromiumos/src/platform/ec
 (chroot) $ make BOARD=servo_v4 -j8
 ```

 To raw flash a Servo v4, `BOOT0` select pin is indicated by the OTG cable:

 ```bash
 (chroot) $ ./util/flash_ec --board=servo_v4
 ```

 To set the Servo v4 serial number on the Servo console:

 ```
 > serialno set 012345
 ```

 [Servo]: ./servo.md
 [Servo v4 Block Diagram]: https://docs.google.com/drawings/d/1Ba0ut5-MeAOKpLQZ7nFbEaxFD_kFMGIIQmF6SxBUjc4/edit
 [Servo v4 Schematic]: https://docs.google.com/a/chromium.org/viewer?a=v&pid=sites&srcid=Y2hyb21pdW0ub3JnfGRldnxneDo1ZmQ5NjFmMGZlZjFiYjk5
 [Servo Micro]: ./servo.md
 [EC]: https://chromium.googlesource.com/chromiumos/platform/ec
 [`servod`]: ./servod.md
 [SuzyQ]: ./ccd.md#suzyq-suzyqable
 [CCD]: ./ccd.md
 [`FlashAP`]: https://chromium.googlesource.com/chromiumos/platform/ec/+/cr50_stab/docs/case_closed_debugging_cr50.md#flashap
 [Bug]: https://issuetracker.google.com/issues/new?component=983411&template=1678684
 [`hdctools`]: https://chromium.googlesource.com/chromiumos/third_party/hdctools
	# Servo v4

	Servo v4 is a debug device in the Servo family.

	Servo v4 functions as a configurable USB hub to support developer and lab
	recovery features. However, it doesn't have any hardware debug features on its
	own. It must be paired with CCD (GSC's on-board servo implementation) or
	[Servo Micro].

	[TOC]

	## What is Servo v4?

	Servo v4 combines the functionality of the following devices into one:

	* Ethernet-USB dongle
	* Muxable USB port
	* microSD to USB3.0 dongle
	* Keyboard emulator
	* Pass through charger
	* [Case-Closed Debug (CCD)][CCD] interface ([SuzyQ] debug cable)

	Details:

	* [Servo v4 Block Diagram]
	* [Servo v4 Schematic]

	![Servo v4 with Accessories](images/servo_v4.jpg)

	## Getting Servo v4

	<!-- mdformat off(b/139308852) -->
	*** promo
	Sorry, Servo v4 is not publicly available for purchase.
	***
	<!-- mdformat on -->

	<!-- mdformat off(b/139308852) -->
	*** note
	IMPORTANT: You will need to [update the firmware](#updating-firmware)
	before using, as the factory firmware is quite old.
	***
	<!-- mdformat on -->

	### Partners

	Your contact at Google should be able to provide you with Servo v4.

	### Googlers

	Stop by your local Chromestop, or use http://go/hwrequest and enter `Servo V4`
	for the `Google Code Name`.

	## How to Use Servo v4

	The plastic case has labels `HOST`, `DUT POWER`, and `uSERVO`.

	* `HOST`: Servo v4 can be plugged into a host machine using a micro-B USB
	cable via the micro-B USB port marked `HOST`. This will power Servo v4 while
	allowing the user to control Servo v4 using [`servod`].

	* `DUT POWER`: USB-C port labeled `DUT POWER` is for powering the DUT through
	the Servo. Servo v4 can be used to power the DUT which becomes useful for
	devices that use USB-C as their only charge port (tablets, phones etc.). The
	Type-C port can be used to plug in any Type-C charger to provide full
	charging capabilities as a charge through hub. If no charger is plugged,
	Servo v4 will act as a passive hub.

	* `uSERVO`: On the side labeled `uSERVO` there are two connectors.

	* The DUT connector (which is a captive cable: servo side is permanently
	connected) can be plugged into a DUT, providing the DUT access to the
	ethernet and blue USB port. The Type-C captive cable enables debugging
	of devices that have a GSC (recent Chromebooks) through [CCD].

	* The "uServo" USB port can be used to plug a servo micro to debug DUT
	over the Yoshi debug header.

	* The following ports on the unlabeled side can be used to download data to a
	device:

	* Ethernet
	* microSD card
	* USB stick

	Servo v4 has an embedded keyboard so keystrokes can be emulated on the DUT.

	The [`servod`] server must be running for Servo v4 to work. Details can be found
	on the [Servo] page.

	## Type-A vs Type-C Variants

	There are two variants of Servo V4: Type-A and Type-C.

	Both versions use the same board and case, but have a different captive cable
	stuffed.

	### Type-C Version

	The Type-C version acts as both a USB hub and PD charger. Servo v4 can also
	control both CC terminations which allows it to act as a debug accessory. It
	should be used on systems with [CCD].

	<!-- mdformat off(b/139308852) -->
	*** note
	NOTE: Type-C Servo v4 is a charge-through hub and is NOT functionally equivalent
	to a Type-A servo with an A-to-C adapter. DO NOT use a Type-C Servo v4 just
	because you want to plug into a Type-C port. Older Chromebooks (Eve, Samus,
	etc.) have [EC] bugs that prevent charge through hubs from working correctly.
	***
	<!-- mdformat on -->

	![Servo v4 Type-C](images/servo_v4_typec.jpg)

	### Type-A Version

	The Type-A version is used with a uServo and serves as the DUT USB hub, with the
	uServo providing SPI and UART support.

	![Servo v4 Type-A](images/servo_v4_typea.jpg)

	## Servo v4 Revisions

	Servo v4 had several revisions, indicated by board color. The mass production
	(MP) version is available from Chromestop.

	### Green (MP)

	Final version, has full functionality.

	### Blue (DVT)

	The DVT version is completely functional except for the one bug affecting only
	Type-C variant. There are about one thousand of these, so you may encounter
	them.

	* PD Charge-through only works on chargers up to 10V.
	* Firmware identifies this by board revision and will not negotiate any
	voltages above 10V.

	### Red (EVT)

	The EVT version is a mostly functioning version with a few bugs. There are
	around three hundred of these total.

	* The ethernet IC has a bug in it that makes the device fall out of
	GigE/USB3.0 speeds under certain circumstances and it falls down to USB1.1 /
	2 speeds and never properly recovers until reset.
	* Type-C variant doesn't function, Type-A works OK.

	## Software

	Servo v4 runs more or less equivalently to Servo v2, through [`servod`].
	It's intended to be mostly transparent, but there are some differences.

	Most functionality is exported through `dut-control`.

	```bash
	(HOST) $ start-servod -b <board> -s <serial>
	```

	To use with a specific board, you can connect a servo_micro to the "uServo"
	labeled port (or use the Type-C cable to connect to [CCD]) and run [`servod`],
	which will load the board config and control both Servo v4 and Servo Micro (or
	GSC).

	```bash
	(HOST) $ start-servod -b [board] -s [serialno printed on servo v4 sticker]
	```

	### Recipes

	#### Connect to Servo_v4 console with Servod

	```bash
	(HOST) $ minicom -D "$(dut-control -- -o servo_v4_uart_pty)"
	```

	#### Connect to Servo consoles without servod

	When Servos are plugged in, it creates several console endpoints starting at
	`/dev/ttyUSB0` and incrementing based on the hardware present. If you connect
	to these you can directly interact with the Servo firmware STM32 or DUT shells.
	Not all shells will be active depending on device setup.

	```bash
	(HOST) $ minicom -D /dev/ttyUSB0
	> version
	Chip: stm stm32f07x
	Board: 3
	RO: servo_v4p1_v2.0.24151-03b2123fb
	```

	#### Switch SD to Host

	```bash
	(HOST) $ dut-control -- sd_en:on sd_pwr_en:on sd_mux_sel:servo_sees_usbkey host_sd_usb_mux_en:on host_sd_usb_mux_sel:sd
	```

	#### Switch SD to DUT

	```bash
	(HOST) $ dut-control -- sd_en:on sd_pwr_en:on sd_mux_sel:dut_sees_usbkey
	```

	#### Disable SD

	```bash
	(HOST) $ dut-control -- sd_en:off sd_pwr_en:off
	```

	#### Switch USB3 to Host

	```bash
	(HOST) $ dut-control -- usb3_mux_en:on usb3_mux_sel:servo_sees_usbkey usb3_pwr_en:on host_sd_usb_mux_en:on host_sd_usb_mux_sel:usb
	```

	#### Switch USB3 to DUT

	```bash
	(HOST) $ dut-control -- usb3_mux_en:on usb3_mux_sel:dut_sees_usbkey usb3_pwr_en:on
	```

	### Disable/Enable [SuzyQ] wiring (debug accessory mode)

	<!-- mdformat off(b/139308852) -->
	*** note
	Type-C Servo v4 only
	***
	<!-- mdformat on -->

	```bash
	(HOST) $ dut-control -- servo_v4_dts_mode:off [on]
	```

	#### Connect remotely

	```bash
	(HOST) $ dut-control -- --host XXX --port YYY
	```

	### Disable/Enable Chargethrough

	<!-- mdformat off(b/139308852) -->
	*** note
	Type-C Servo v4 only
	***
	<!-- mdformat on -->

	```bash
	(HOST) $ dut-control -- servo_v4_role:snk [src]
	```

	## Firmware flashing and reading

	<!-- mdformat off(b/139308852) -->
	*** note
	When flashing the BIOS or EC with [CCD], you need to make sure the [`FlashAP`]
	capability is enabled in GSC.
	***
	<!-- mdformat on -->

	Read and flash AP firmware (BIOS) with CCD or any other servo debug connection:

	```bash
	(chroot) $ sudo futility read --servo -v "$OUTFILE"
	(chroot) $ sudo futility update --servo -v -i "$INFILE"
	```

	## Updating Firmware {#updating-firmware}

	The latest firmware is available via the servod docker image. You need to have go/servod
	configured. That would also add servo_updater CLI to your host shell.

	<!-- mdformat off(b/139308852) -->
	*** note
	NOTE: [`servod`] must not be running. You should have recent versions of
	start-servod and servo_updater scripts that are in hdctools repo (repo sync)

	***
	<!-- mdformat on -->

	Update to latest stable firmware:

	```bash
	(HOST) $ servo_updater -- -b servo_v4
	```

	Rollback to previous stable version if needed:
	```bash
	(HOST) $ servo_updater -- -b servo_v4 -c prev --allow-rollback
	```
	---
	Advanced usage below:

	- Update to specific binary file

	```bash
	(HOST) $ servo_updater -f <file_path> -- -b servo_v4
	```

	- Update to specific FW channel

	```bash
	(HOST) $ servo_updater -- -b servo_v4 -c [alpha\|dev\|prev\|stable]
	```

	- If you need to update FW, before it reaches monthly released servod image specify
	channel for servod docker distribution ("release" is default)

	```bash
	(HOST) $ servo_updater --updater_channel [local\|latest\|beta\|release] -- -c [alpha\|dev\|prev\|stable] -b servo_v4 [...]
	```

	## Enabling Case Closed Debug (CCD)

	See [CCD] for complete details.

	<!-- mdformat off(b/139308852) -->
	*** note
	If using a Type-C Servo v4, these commands will only work if the USB-C cable is
	plugged into the correct USB port. Generally, this is the USB port on the left
	side of the device. If the command doesn't work, try the other ports.
	***
	<!-- mdformat on -->

	Connect to GSC console:

	```bash
	(HOST) $ minicom -D "$(dut-control -- -o gsc_uart_pty)"
	```

	Check the GSC FW version in the GSC console:

	```
	> version
	Build: 0.4.10/cr50_v1.9308_B.269-754117a
	```

	<!-- mdformat off(b/139308852) -->
	***note
	CCD requires Cr50 version 0.3.9+ / 0.4.9+
	* 0.4.x is the "pre-pvt" version, for pre-production devices.
	* 0.3.x is the "mp" version, for production devices. This requires the device
	to be in developer mode before "ccd open".
	* 0.0.22 is the factory preflash from GUC. It needs an update.
	***
	<!-- mdformat on -->

	Open CCD in the GSC console:

	```
	> ccd open
	```

	Press power button when prompted. It should take around 5 minutes.

	<!-- mdformat off(b/139308852) -->
	*** note
	If you get an access denied error when attempting `ccd open`, you likely do
	not have developer mode enabled.
	***
	<!-- mdformat on -->

	<!-- mdformat off(b/139308852) -->
	*** note
	GSC loses the developer mode state after "opening CCD". If your device boots
	into recovery mode, try re-entering developer mode.
	***
	<!-- mdformat on -->

	Enable testlab mode in the GSC console:

	```
	> ccd testlab enable
	```

	Press power button some more. CTRL+C to exit.

	Run [`servod`] as normal, [CCD] should be enabled now.

	## Known issues

	* Displayport - not supported
	* Type-A/Type-C: Servo V4 comes in two variants on the captive cable, both can
	be obtained from Chromestop.
	* Type-C Servo is not interchangeable with Type-A. Type-C must be paired with
	CCD, Type-A must be paired with Servo Micro.
	* DFU: To use util/flash_ec you must enable DFU by connecting servo with an
	A-A cable plugged into an OTG cable. USB ID is tied to BOOT0 indicator on
	the STM32 part.

	### Interop Problems with Some Switches

	See http://b/112187276.

	Your network switch port will get hosed (some TX buffer fills up and starts
	dropping things) if you have Servo v4 connected to most switches and unplug the
	servo's USB connection, or power off the DUT fully, after the servo's NIC has an
	IP. This behavior is not reproducible with a [GS108Tv2], so the workaround is to
	use a [GS108Tv2].

	[GS108Tv2]: https://www.amazon.com/NETGEAR-Ethernet-Unmanaged-Lifetime-Protection/dp/B003KP8VSK/

	## Bugs

	File bug or feature requests [here][Bug].

	## Programming

	<!-- mdformat off(b/139308852) -->
	*** note
	You don't need to do this unless you're developing Servo v4 firmware.
	***
	<!-- mdformat on -->

	Servo v4 code lives in the [EC] and [`hdctools`] codebase. It can be built as
	follows:

	```bash
	(chroot) $ cd ~/chromiumos/src/platform/ec
	(chroot) $ make BOARD=servo_v4 -j8
	```

	To raw flash a Servo v4, `BOOT0` select pin is indicated by the OTG cable:

	```bash
	(chroot) $ ./util/flash_ec --board=servo_v4
	```

	To set the Servo v4 serial number on the Servo console:

	```
	> serialno set 012345
	```

	[Servo]: ./servo.md
	[Servo v4 Block Diagram]: https://docs.google.com/drawings/d/1Ba0ut5-MeAOKpLQZ7nFbEaxFD_kFMGIIQmF6SxBUjc4/edit
	[Servo v4 Schematic]: https://docs.google.com/a/chromium.org/viewer?a=v&pid=sites&srcid=Y2hyb21pdW0ub3JnfGRldnxneDo1ZmQ5NjFmMGZlZjFiYjk5
	[Servo Micro]: ./servo.md
	[EC]: https://chromium.googlesource.com/chromiumos/platform/ec
	[`servod`]: ./servod.md
	[SuzyQ]: ./ccd.md#suzyq-suzyqable
	[CCD]: ./ccd.md
	[`FlashAP`]: https://chromium.googlesource.com/chromiumos/platform/ec/+/cr50_stab/docs/case_closed_debugging_cr50.md#flashap
	[Bug]: https://issuetracker.google.com/issues/new?component=983411&template=1678684
	[`hdctools`]: https://chromium.googlesource.com/chromiumos/third_party/hdctools