path: root/docs/fingerprint/fingerprint-dev-for-partners.md

# FPMCU Development for Partners

This document is intended to help partners (sensor vendors, MCU vendors, etc)
that are currently (or interested in) developing fingerprint solutions for
Chromebooks. The document assumes that you're using Linux to do the development;
preferably a recent version of Ubuntu or Debian. Some partners have had success
developing in a VM, but please note that we don't test that configuration.

See the [FPMCU documentation] for additional development information.

[TOC]

## Hardware Required for Standalone Development (no Chromebook)

The following hardware components can be used to set up a standalone development
environment for FPMCU development (i.e., it does not rely on a Chromebook).
Development for other [EC]s is often done in a similar manner, but some of them
have their own standalone development or evaluation kits that don't require the
use of [servo].

You will need an [FPMCU reference board](#fpmcu-dev-board) and a
[servo debugger](#servo).

### FPMCU board {#fpmcu-dev-board}

The Fingerprint MCU (FPMCU) board has the MCU that handles all
fingerprint-related functionality (matching, encryption, etc). The fingerprint
sensor itself connects to the FPMCU board.

This FPMCU board is the Dragonclaw Rev 0.2. |
------------------------------------------- |
![Dragonclaw board]                         |

Download the [Dragonclaw schematics, layout, and BOM][dragonclaw schematics].

<!-- mdformat off(b/139308852) -->
*** note
**Googlers**: You can pick up the Dragonclaw development board at Chromestop.
**Partners**: You can request a Dragonclaw development board from Google.
***

*** note
Dragonclaw Rev 0.2 needs a [rework](#dragonclaw-rev-0.2-rework) for the FPC
sensor to work while being powered through Servo. All of the boards at Chromestop
have already been reworked.
***
<!-- mdformat on -->

This FPMCU board is the Dartmonkey Rev 0.1. |
------------------------------------------- |
![Dartmonkey board]                         |

### Servo

Servo is a general purpose debug board that connects to a header on the FPMCU
board. Among other things, the servo supplies power to the FPMCU and can be used
to program the FPMCU, interact with the EC console, take power measurements, and
debug a running program. It supports SPI, UART, I2C, as well as JTAG/SWD.

There are two different servo debugger setups supported, the
[Servo Micro](#servo-micro) and the [Servo V2 + Yoshi](#servo-v2-yoshi). The
servo micro is recommended for its simplicity. It lacks builtin JTAG/SWD support
for single step debugging, but Dragonclaw v0.2 has an
[SWD connector](#servo-micro-swd) that can be used.

[Servo Micro](#servo-micro) | [ServoV2 + Yoshi](#servo-v2-yoshi)
--------------------------- | ----------------------------------
![Servo Micro]              | ServoV2 ![Servo v2] Yoshi Flex ![Standard Yoshi Flex]

<!-- mdformat off(b/139308852) -->
*** note
For more information about both servos, see [servo].
***
<!-- mdformat on -->

### Servo Micro

Unlike the Servo V2, the newer servo micro does not require any adapters to
interface with the FPMCU board.

As you can see below, one end connects to the FPMCU board and the other connect
to the developer's computer over micro USB.

![Servo Micro with Dragonclaw]

<!-- mdformat off(b/139308852) -->
*** note
For more information about Servo Micro, see [Servo Micro Info].
***
<!-- mdformat on -->

#### Using SWD (Optional) {#servo-micro-swd}

Instructions for setup are described in [Fingerprint Debugging].

### Servo V2 + Yoshi

Servo V2 is the original full featured debugger. It requires a
[Yoshi Flex Cable](#yoshi-flex-cable) to interface with the FPMCU.

![Servo v2]

<!-- mdformat off(b/139308852) -->
*** note
NOTE: More information on servo can be found in the [servo] documentation.
***
<!-- mdformat on -->

#### Yoshi Flex Cable

The Yoshi Flex cable is used to connect Servo v2 to the FPMCU board. The
standard cable does not work with SWD, but a simple rework can be performed to
support SWD.

Standard Yoshi Flex    | Yoshi Flex Reworked to Support SWD
---------------------- | -------------------------------------
![Standard Yoshi Flex] | ![Yoshi Flex Reworked to Support SWD]

Rework steps:

*   Remove R18 and R19
*   Wire from Pin 6 of U21 to right side of R18
*   Wire from Pin 6 of U21 to right side of R19

#### Micro USB Cable

A micro USB cable is needed to connect the the servo v2 board to your host Linux
development machine.

*   [Micro USB Cable]

#### Servo V2 Hardware Setup

1.  Connect the Yoshi Flex cable to servo, paying attention to the pin
    numbering.

    ![Connect Yoshi Flex] ![Another Yoshi Flex image]

2.  Connect the other end of the Yoshi Flex cable to the servo header on the
    FPMCU board.

    ![Connect Yoshi Flex to FPMCU board] ![Another image]

3.  Connect the fingerprint sensor to the header on the FPMCU board.

4.  Connect the micro USB cable to servo's `HOST_IN` port. The other end of the
    USB cable should be plugged into your host development machine.

    ![Connect USB to Servo]

5.  Optional: Connect SWD Debugger

    If you want to use SWD for debugging, connect your debugger to the `JTAG`
    header on servo v2.

    ![Connect SWD Debugger]

## Software Setup

### Get the Chromium OS source code

*   First, make sure you [have the prerequisites].
*   Then [get the source].
*   Create and [enter the `chroot`].
    *   You can stop after the `enter the chroot` step.

### Build the [EC]\ (embedded controller) codebase

Open **two** terminals and enter the chroot in each:

```bash
# from a terminal on your machine
(outside chroot) $ cd ~/chromiumos/src

# enter the chroot (the flag is important)
(outside chroot) $ cros_sdk --no-ns-pid
```

<!-- mdformat off(b/139308852) -->
*** note
NOTE: More information on servo can be found in the [servo] documentation.
***
<!-- mdformat on -->

In one of the terminals, build and start `servod`

Build and install `servod` in the chroot:

```bash
(chroot) $ sudo emerge hdctools
```

<!-- mdformat off(b/139308852) -->
*** note
In all of the following commands, replace `<BOARD>` in the command with
`bloonchipper` or `dartmonkey` depending on the development board you are using.
***
<!-- mdformat on -->

Run `servod`:

```bash
(chroot) $ sudo servod --board=<BOARD>
```

You should see something like this. Leave it running:

```bash
2019-04-11 15:21:53,715 - servod - INFO - Start
2019-04-11 15:21:53,765 - servod - INFO - Found servo, vid: 0x18d1 pid: 0x5002 sid: 911416-00789
2019-04-11 15:21:53,766 - servod - INFO - Found XML overlay for board zerblebarn
2019-04-11 15:21:53,766 - SystemConfig - INFO - Loading XML config (/usr/lib64/python2.7/site-packages/servo/data/servo_v2_r1.xml, None, 0)
2019-04-11 15:21:53,767 - SystemConfig - INFO - Loading XML config (/usr/lib64/python2.7/site-packages/servo/data/servo_v2_r0.xml, None, 0)
2019-04-11 15:21:53,771 - SystemConfig - INFO - Loading XML config (/usr/lib64/python2.7/site-packages/servo/data/common.xml, None, 0)
2019-04-11 15:21:53,772 - SystemConfig - INFO - Loading XML config (/usr/lib64/python2.7/site-packages/servo/data/power_tools.xml, None, 0)
2019-04-11 15:21:53,774 - SystemConfig - INFO - Loading XML config (/usr/lib64/python2.7/site-packages/servo/data/keyboard.xml, None, 0)
2019-04-11 15:21:53,775 - SystemConfig - INFO - Loading XML config (/usr/lib64/python2.7/site-packages/servo/data/uart_common.xml, None, 0)
2019-04-11 15:21:53,777 - SystemConfig - INFO - Loading XML config (/usr/lib64/python2.7/site-packages/servo/data/ftdii2c_cmd.xml, None, 0)
2019-04-11 15:21:53,777 - SystemConfig - INFO - Loading XML config (/usr/lib64/python2.7/site-packages/servo/data/usb_image_management.xml, None, 0)
2019-04-11 15:21:53,784 - SystemConfig - INFO - Loading XML config (/usr/lib64/python2.7/site-packages/servo/data/servo_zerblebarn_overlay.xml, None, 0)
2019-04-11 15:21:53,785 - SystemConfig - INFO - Loading XML config (/usr/lib64/python2.7/site-packages/servo/data/servoflex_v2_r0_p50.xml, None, 0)
2019-04-11 15:21:53,792 - Servod - INFO - Initializing interface 1 to ftdi_empty
2019-04-11 15:21:53,792 - Servod - INFO - Initializing interface 2 to ftdi_i2c
2019-04-11 15:21:53,795 - Servod - INFO - Initializing interface 3 to ftdi_uart
2019-04-11 15:21:53,799 - Servod - INFO - /dev/pts/8
2019-04-11 15:21:53,799 - Servod - INFO - Initializing interface 4 to ftdi_uart
2019-04-11 15:21:53,802 - Servod - INFO - /dev/pts/9
2019-04-11 15:21:53,802 - Servod - INFO - Use the next FTDI part @ pid = 0x5003
2019-04-11 15:21:53,802 - Servod - INFO - Initializing interface 5 to ftdi_empty
2019-04-11 15:21:53,802 - Servod - INFO - Use the next FTDI part @ pid = 0x5003
2019-04-11 15:21:53,802 - Servod - INFO - Initializing interface 6 to ftdi_empty
2019-04-11 15:21:53,802 - Servod - INFO - Use the next FTDI part @ pid = 0x5003
2019-04-11 15:21:53,802 - Servod - INFO - Initializing interface 7 to ftdi_uart
2019-04-11 15:21:53,805 - Servod - INFO - /dev/pts/10
2019-04-11 15:21:53,805 - Servod - INFO - Use the next FTDI part @ pid = 0x5003
2019-04-11 15:21:53,805 - Servod - INFO - Initializing interface 8 to ftdi_uart
2019-04-11 15:21:53,808 - Servod - INFO - /dev/pts/11
2019-04-11 15:21:53,808 - Servod - INFO - Initializing interface 9 to ec3po_uart
2019-04-11 15:21:53,811 - PD/Cr50 - EC3PO Interface - INFO - -------------------- PD/Cr50 console on: /dev/pts/12
2019-04-11 15:21:53,811 - Servod - INFO - Initializing interface 10 to ec3po_uart
2019-04-11 15:21:53,812 - EC - EC3PO Interface - INFO - -------------------- EC console on: /dev/pts/14
2019-04-11 15:21:54,316 - Servod - INFO - Initialized i2c_mux to rem
2019-04-11 15:21:54,317 - Servod - INFO - Initialized i2c_mux_en to on
2019-04-11 15:21:54,319 - Servod - INFO - Initialized pch_disable to off
2019-04-11 15:21:54,320 - Servod - INFO - Initialized jtag_buf_on_flex_en to off
2019-04-11 15:21:54,321 - Servod - INFO - Initialized cold_reset to off
2019-04-11 15:21:54,322 - Servod - INFO - Initialized warm_reset to off
2019-04-11 15:21:54,323 - Servod - INFO - Initialized spi1_buf_on_flex_en to off
2019-04-11 15:21:54,324 - Servod - INFO - Initialized spi_hold to off
2019-04-11 15:21:54,326 - Servod - INFO - Initialized pwr_button to release
2019-04-11 15:21:54,327 - Servod - INFO - Initialized lid_open to yes
2019-04-11 15:21:54,328 - Servod - INFO - Initialized spi2_buf_on_flex_en to off
2019-04-11 15:21:54,330 - Servod - INFO - Initialized rec_mode to off
2019-04-11 15:21:54,331 - Servod - INFO - Initialized fw_up to off
2019-04-11 15:21:54,332 - Servod - INFO - Initialized usb_mux_sel1 to dut_sees_usbkey
2019-04-11 15:21:54,333 - Servod - INFO - Initialized prtctl4_pwren to on
2019-04-11 15:21:54,334 - Servod - INFO - Initialized uart3_en to on
2019-04-11 15:21:54,334 - Servod - INFO - Initialized dut_hub_pwren to on
2019-04-11 15:21:54,335 - Servod - INFO - Initialized kbd_en to off
2019-04-11 15:21:54,337 - Servod - INFO - Initialized spi1_vref to pp3300
2019-04-11 15:21:54,338 - Servod - INFO - Initialized spi2_vref to pp1800
2019-04-11 15:21:54,339 - Servod - INFO - Initialized uart2_en to on
2019-04-11 15:21:54,340 - Servod - INFO - Initialized uart1_en to on
2019-04-11 15:21:54,341 - Servod - INFO - Initialized jtag_buf_en to off
2019-04-11 15:21:54,342 - Servod - INFO - Initialized fw_wp_en to off
2019-04-11 15:21:54,343 - Servod - INFO - Initialized sd_vref_sel to off
2019-04-11 15:21:54,343 - Servod - INFO - Initialized ec_ec3po_interp_connect to on
2019-04-11 15:21:54,344 - Servod - INFO - Initialized uart3_vref to off
2019-04-11 15:21:54,345 - Servod - INFO - Initialized jtag_vref_sel0 to pp3300
2019-04-11 15:21:54,346 - Servod - INFO - Initialized jtag_vref_sel1 to pp3300
2019-04-11 15:21:54,346 - Servod - INFO - Initialized fpmcu_ec3po_interp_connect to on
2019-04-11 15:21:54,349 - ServoDeviceWatchdog - INFO - Watchdog setup for devices: set([(6353, 20482, '911416-00789')])
2019-04-11 15:21:54,351 - servod - INFO - Listening on localhost port 9999
```

In the other terminal, build and flash the firmware:

Navigate to the EC source:

```bash
(chroot) $ cd ../platform/ec
```

Build the firmware:

```bash
(chroot) $ make BOARD=<BOARD> -j
```

The resulting file will be in `build/<BOARD>/ec.bin`

Flash the firmware file:

```bash
(chroot) $ ./util/flash_ec --board=<BOARD> --image=./build/<BOARD>/ec.bin
```

Prepare a serial terminal in your chroot:

```bash
(chroot) $ sudo emerge screen
```

Connect to the UART pty:

```bash
(chroot) $ sudo screen $(dut-control raw_fpmcu_console_uart_pty | cut -d: -f2)
```

Press enter key several times (may need to wait up to 20 seconds). Then you will
see a prompt:

```
>
```

At this point you are connected to the MCU's serial (UART) console. You can list
all of the available console commands with "help":

```
> help
```

```bash
Known commands:
  chan           fpcapture      hcdebugsherase     fpenroll       history        spixfer        waitms
  flashinfo      fpmatch        hostevent      sysinfo
  flashread      gettime        md             sysjump
  flashwp        gpioget        panicinfo      syslock
  flashwrite     gpioset        reboot         taskinfo
HELP LIST = more info; HELP CMD = help on CMD.
```

Start a fingerprint enrollment:

```
> fpenroll
```

### Measuring Power {#measure-power}

The Dragonclaw reference board has an onboard INA that monitors the voltage and
power draw of the MCU and FP Sensor independently.

Signal Name     | Description
--------------- | -------------------------------------
`pp3300_dx_mcu` | 3.3V supplying the MCU
`pp3300_dx_fp`  | 3.3V supplying the fingerprint sensor
`pp1800_dx_fp`  | 1.8V supplying the fingerprint sensor

You can monitor all power and voltages by using the following command:

```bash
(chroot) $ watch -n0.5 dut-control pp3300_dx_mcu_mv pp3300_dx_fp_mv pp1800_dx_fp_mv pp3300_dx_mcu_mw pp3300_dx_fp_mw pp1800_dx_fp_mw
```

You can get a summary of the power over `N` seconds with:

```bash
(chroot) $ dut-control -t N pp3300_dx_mcu_mv pp3300_dx_fp_mv pp1800_dx_fp_mv pp3300_dx_mcu_mw pp3300_dx_fp_mw pp1800_dx_fp_mw
```

<!-- mdformat off(b/139308852) -->
*** note
The `_mv` suffix denotes millivolt and `_mw` suffix denotes milliwatt.
***

*** note
See [Power Measurement Documentation] for more information.
***
<!-- mdformat on -->

### Toggling Hardware Write Protect

When using a fingerprint development board connected to servo, you can toggle
hardware write protect for testing.

**NOTE**: `servod` must be running.

Check the state of hardware write protect:

```bash
(chroot) $ dut-control fw_wp_en
```

Enable hardware write protect:

```bash
(chroot) $ dut-control fw_wp_en:on
```

Disable hardware write protect:

```bash
(chroot) $ dut-control fw_wp_en:off
```

### Contributing Changes

#### Using Gerrit and git

If you’re not familiar with `git`, Gerrit (code review) and `repo`, here are
some docs to help you get started:

*   [Git and Gerrit Intro for Chromium OS]: Useful to get started as quickly as
    possible, but does not explain how `git` works under the hood.
*   [Set your editor]: Use your favorite editor when writing `git` commit
    messages.
*   [Chromium OS Contributing Guide]: Detailed overview of contributing changes
    to Chromium OS and the workflow we use.
*   [Git: Concepts and Workflow]: Good overview of how `git` actually works.
*   [Gerrit: Concepts and Workflow]: Good overview of how Gerrit works; assumes
    you understand `git` basics.
*   [Life of a patch]: Android workflow, but similar to Chrome OS.

The Gerrit dashboard that will show your pending reviews (and ones we have for
you):

*   [Public Gerrit]
*   [Internal Gerrit]

#### Registering for a chromium.org *Internal* Account

If your partnership agreement requires non-public code sharing you will need to
register for an account on the [Internal Gerrit]. Refer to the
[Gerrit Credentials Setup] page for details. Once you register for an internal
account, your contact at Google can make sure you have the necessary permissions
to access the private repository.

<!-- mdformat off(b/139308852) -->
*** note
**NOTE**: In order to use a private repository you will have to manually add it
to the repo manifest file before running `repo sync`. Check with your contact
at Google for the exact values to use below:

**`(outside) $ ~/chromiumos/.repo/manifests/default.xml`**

```xml
<project remote="cros-internal"
         path="CHECK WITH GOOGLE"
         groups="firmware"
         name="CHECK WITH GOOGLE" />
```

**`(outside) $ ~/chromiumos/.repo/manifests/remote.xml`**

```xml
<remote name="cros-internal"
        fetch="https://chrome-internal.googlesource.com"
        review="https://chrome-internal-review.googlesource.com" />
```
***
<!-- mdformat on -->

### Tracking Issues and Communication

Development issue tracking and communication is done through the
[Partner Issue Tracker]. You will use your [Partner Domain] account to access
the [Partner Issue Tracker]. If you do not already have a [Partner Domain]
account, please request one from your Google contact.

In order to make sure that you receive email notifications for issues, please
make sure that you [set up email forwarding] and set your
[notification settings] appropriately. Communication should primarily be done
through the [Partner Issue Tracker] and not email so that it can be more easily
tracked by multiple people and a record is preserved for posterity.

[Partner Issue Tracker]: https://developers.google.com/issue-tracker/guides/partner-access
[Partner Domain]: https://developers.google.com/issue-tracker/guides/partner-domains
[set up email forwarding]: https://developers.google.com/issue-tracker/guides/partner-domains#email_forwarding
[notification settings]: https://developers.google.com/issue-tracker/guides/set-notification-preferences

## Working with Chromebooks

Chromebooks have an FPMCU (e.g., Dragonclaw) board attached to the motherboard.
You can use the device to run `ectool` commands and test the fingerprint sensor
from the UI.

### Developer Mode and Write Protection

Make sure that your fingerprint-equipped Chrome OS device is in [developer mode]
with a *test* image flashed and [hardware write protection] disabled. Using the
test image will allow you to SSH into the device and disabling hardware write
protection allows you to have full access to flashing the FPMCU firmware.

See [Installing Chromium] for details on flashing test images and enabling
[developer mode].

### Connecting

In general, most of our development is done by connecting to the DUT (device
under test) via SSH. We usually connect the DUT to ethernet (e.g., via USB-C to
Ethernet converter), but WiFi should also work (assuming corporate firewall
restrictions don’t block SSH port 22). To get the IP address, tap the
battery/time icon in the lower right corner. Then tap on “Ethernet” followed by
the gear icon in the upper right.

```bash
(chroot) $ ssh root@<IP_ADDRESS>
Password: test0000
```

Once you have SSH’ed into the DUT, you should be able to run `ectool` commands.

**Example**: Capture a "test_reset" image from the sensor and write it to a
[PNM] file (viewable with the ImageMagick `display` command):

```bash
(device) $ ectool --name=cros_fp fpmode capture test_reset; ectool --name=cros_fp waitevent 5 500; ectool --name=cros_fp fpframe > /tmp/test_reset.pnm
```

Alternatively, you can access a shell via the UI on device by pressing
`CTRL+ALT+F2` (third key on top row). Log in with `root` and `test0000`.

### Flashing FPMCU from DUT

Copy the firmware to the DUT:

```bash
(chroot) $ scp ./build/bloonchipper/ec.bin <DUT_IP>:/tmp/ec.bin
```

From the DUT, flash the firmware you copied:

```bash
(device) $ flash_fp_mcu /tmp/ec.bin
```

## Commit-queue Prototype Environment

![CQ Prototype Environment]

## Troubleshooting

### Dragonclaw Rev 0.2 Rework {#dragonclaw-rev-0.2-rework}

<!-- mdformat off(b/139308852) -->
*** note
**NOTE**: All Dragonclaw v0.2 boards have been reworked, so it is not necessary
to perform the rework yourself.
***
<!-- mdformat on -->

Dragonclaw **Rev 0.2** has two load switches (`U4` and `U6`) that enable the
1.8V power rail from the servo connector or motherboard connector. However, this
switch is not compatible with 1.8V, so will always output 0V.

The [rework document][Dragonclaw Rev 0.2 1.8V Rework] describes replacing these
two switches with ones compatible with 1.8V.

### Dragonclaw Rev 0.1 Servo Fix

Dragonclaw **Rev 0.1** has a known issue with UART and JTAG. Most notably, this
issue causes servo micro to fail to program the FPMCU over UART.

This issue can be fixed with the following rework steps:

*   Connect servo header pin 13 to pin 18
*   Connect servo header pin 13 to pin 29

![Dragonclaw servo fix diagram]

### Verify that servo and debugger are connected to USB {#servo-connected}

Check whether servo is enumerating on USB. If you are using a debugger
(Lauterbach, J-Link, etc), also check to make sure it enumerates. Depending on
the debugger being used, it may need to be powered with an external power
supply.

```bash
(chroot) $ lsusb

Bus 002 Device 003: ID 0897:0004 Lauterbach  # ← This is my Lauterbach (debugger)
Bus 001 Device 013: ID 18d1:5002 Google Inc. # ← This is servo
```

### "No servos found" when running servod

If you get the following message, make sure that
[servo is connected to USB](#servo-connected). You may also want to try
restarting your machine (or VM).

```bash
(chroot) $ sudo servod --board=bloonchipper
2019-04-12 14:53:42,236 - servod - INFO - Start
2019-04-12 14:53:42,270 - servod - ERROR - No servos found
```

### Losing characters in servo UART console

Make sure that this interface is disabled:

```bash
(chroot) $ dut-control usbpd_ec3po_interp_connect:off
```

### FPMCU console commands

*   Once the console is working you can use `help` to see the commands.
*   There should be fingerprint commands that start with `fp` (see `fpsensor.c`
    in the [EC] code).

<!-- Links -->

[EC]: https://chromium.googlesource.com/chromiumos/platform/ec
[ectool_servo_spi]: https://chromium.googlesource.com/chromiumos/platform/ec/+/HEAD/util/comm-servo-spi.c#15
[servo]: https://chromium.googlesource.com/chromiumos/third_party/hdctools/+/HEAD/README.md
[developer mode]: https://chromium.googlesource.com/chromiumos/docs/+/HEAD/debug_buttons.md#firmware-keyboard-interface
[hardware write protection]: https://chromium.googlesource.com/chromiumos/platform/ec/+/HEAD/docs/write_protection.md
[have the prerequisites]: https://chromium.googlesource.com/chromiumos/docs/+/HEAD/developer_guide.md#Prerequisites
[get the source]: https://chromium.googlesource.com/chromiumos/docs/+/HEAD/developer_guide.md#get-the-source
[enter the `chroot`]: https://chromium.googlesource.com/chromiumos/docs/+/HEAD/developer_guide.md#building-chromium-os
[Chromium OS Contributing Guide]: https://chromium.googlesource.com/chromiumos/docs/+/HEAD/contributing.md
[Servo Micro Info]: https://chromium.googlesource.com/chromiumos/third_party/hdctools/+/HEAD/docs/servo_micro.md
[Set your editor]: https://chromium.googlesource.com/chromiumos/docs/+/HEAD/developer_guide.md#Set-your-editor
[Life of a patch]: https://source.android.com/setup/contribute/life-of-a-patch
[Git: Concepts and Workflow]: https://docs.google.com/presentation/d/1IQCRPHEIX-qKo7QFxsD3V62yhyGA9_5YsYXFOiBpgkk/
[Gerrit: Concepts and Workflow]: https://docs.google.com/presentation/d/1C73UgQdzZDw0gzpaEqIC6SPujZJhqamyqO1XOHjH-uk/
[Public Gerrit]: https://chromium-review.googlesource.com
[Power Measurement Documentation]: https://chromium.googlesource.com/chromiumos/third_party/hdctools/+/HEAD/docs/power_measurement.md
[Internal Gerrit]: https://chrome-internal-review.googlesource.com
[Gerrit Credentials Setup]: https://www.chromium.org/chromium-os/developer-guide/gerrit-guide
[Micro USB Cable]: https://www.monoprice.com/product?p_id=9762
[PNM]: https://en.wikipedia.org/wiki/Netpbm_format
[Git and Gerrit Intro for Chromium OS]: https://chromium.googlesource.com/chromiumos/docs/+/HEAD/git_and_gerrit_intro.md
[Installing Chromium]: https://chromium.googlesource.com/chromiumos/docs/+/HEAD/developer_guide.md#installing-chromium-os-on-your-device
[FPMCU documentation]: ./fingerprint.md
[Fingerprint Debugging]: ./fingerprint-debugging.md
[dragonclaw schematics]: ../schematics/dragonclaw

<!-- Images -->

[Servo Micro]: ../images/servo_micro.jpg
[Servo Micro with Dragonclaw]: ../images/servomicro_dragonclaw.jpg
[Servo v2]: ../images/servo_v2.jpg
[Standard Yoshi Flex]: ../images/yoshi_flex.jpg
[Yoshi Flex Reworked to Support SWD]: ../images/yoshi_flex_swd_rework.jpg
[Dragonclaw board]: ../images/dragonclaw_rev_0.2.jpg
[Dragonclaw servo fix diagram]: ../images/dragonclaw_servo_fix.jpg
[Connect USB to Servo]: ../images/servo_v2_with_micro_usb.jpg
[Connect Yoshi Flex]: ../images/servo_v2_with_yoshi_flex.jpg
[Another Yoshi Flex image]: ../images/servo_v2_with_yoshi_flex2.jpg
[Connect Yoshi Flex to FPMCU board]: ../images/dragonclaw_yoshi_flex_header.jpg
[Another image]: ../images/dragonclaw_yoshi_flex_header2.jpg
[Connect SWD Debugger]: ../images/servo_v2_jtag_header.jpg
[Dartmonkey board]: ../images/dartmonkey.jpg

<!-- If you make changes to the docs below make sure to regenerate the JPEGs by
     appending "export/pdf" to the Google Drive link. -->

<!-- https://docs.google.com/drawings/d/1YhOUD-Qf69NUdugT6n0cX7o7CWvb5begcdmJwv7ch6I -->

[Dragonclaw Rev 0.2 1.8V Rework]: https://github.com/coreboot/chrome-ec/blob/master/docs/images/dragonclaw_rev_0.2_1.8v_load_switch_rework.pdf

<!-- https://docs.google.com/drawings/d/1w2qbb4AsSxY-KTK2vXZ6TKeWHveWvS3Dkgh61ocu0wc -->

[CQ Prototype Environment]: ../images/CQ_Prototype_Environment.jpg