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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.

[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 ECs 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 and a servo debugger.

FPMCU 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 0.1.

*** note NOTE: Some FPMCU boards need a rework in order to work properly with servo. This fix is visible in the green box above.

See the Dragonclaw Servo Fix section for more detail.

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 and the Servo V2 + Yoshi. The servo micro is recommended for its simplicity, but currently lack builtin JTAG/SWD support for single step debugging.

Servo Micro	ServoV2 + Yoshi
	ServoV2 Yoshi Flex

*** note For more information about both servos, see servo.

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.

*** note For more information about Servo Micro, see Servo Micro Info.

Servo V2 + Yoshi

Servo V2 is the original full featured debugger. It requires a Yoshi Flex Cable to interface with the FPMCU.

*** note NOTE: More information on servo can be found in the servo documentation.

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

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

Connect the Yoshi Flex cable to servo, paying attention to the pin numbering.
Connect the other end of the Yoshi Flex cable to the servo header on the FPMCU board.

*** note Newer FPMCU boards require the ribbon cable to connect in the reverse direction.
Connect the fingerprint sensor to the header on the FPMCU board.
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.
Optional: Connect SWD Debugger

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

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:

# 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

*** note NOTE: More information on servo can be found in the servo documentation.

In one of the terminals, build and start servod

Build and install servod in the chroot:

(chroot) $ sudo emerge hdctools

Run servod:

(chroot) $ sudo servod --board=bloonchipper --config bloonchipper_rev0.1.xml

You should see something like this. Leave it running:

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_dummy
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_dummy
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_dummy
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:

(chroot) $ cd ../platform/ec

Build the firmware:

(chroot) $ make BOARD=bloonchipper -j

The resulting file will be in build/bloonchipper/ec.bin

Flash the firmware file:

(chroot) $ ./util/flash_ec --board=bloonchipper --image=./build/bloonchipper/ec.bin

Connect to the UART pty:

(chroot) $ sudo screen $(dut-control raw_fpmcu_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

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

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:

(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

*** note The _mv suffix denotes millivolt and _mw suffix denotes milliwatt.

*** note See Power Measurement Documentation for more information.

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):

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 necessary repo.

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.

(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):

(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:

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

From the DUT, flash the firmware you copied:

(device) $ flash_fp_mcu /tmp/ec.bin

Troubleshooting

Dragonclaw 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

Verify that servo and debugger are connected to USB

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.

(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. You may also want to try restarting your machine (or VM).

(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:

(chroot) $ dut-control usbpd_ec3po_interp_connect:off

"Sweetberry" board fails to build

If you're trying to run make buildall -j in the EC codebase and the build fails when trying to build the "sweetberry" board, see this bug: https://crbug.com/992082.

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).

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