Cr50 is the firmware that runs on the Google Security Chip. It has support for Case Closed Debugging (CCD). This support is complete enough to replace servo. This doc explains how to setup CCD, so you can access all of the necessary features to develop firmware on your device or control different components. Please run through the basic setup steps before trying to flash the AP firmware. CCD could help recover your device if you flash broken firmware, but if you brick your device before setting up CCD, you may not be able to enable it.
Cr50 CCD was designed to restrict CCD access to device owners. There are CCD privilege levels that can be used to enable access to different CCD capabilities Open, Unlocked, Locked.
All CCD functionality has been assigned to different CCD capabilities. Capability settings can be modified to require certain privilege levels to access the each capability. Setting a capability requirement to IfOpened will require a level of Open to access that capability. A requirement of UnlessLocked will require the device to be Open or Unlocked to access the capability. Setting the requirement to Always will make the capability always accessible.
Owners can use these settings to customize the CCD so it is as open or restricted as they want.
Cr50 is locked by default. Here are all of the Capabilities and their default settings.
| Capability | Default | Function |
|---|---|---|
| UartGscRxAPTx | Always | controls reading from the AP console |
| UartGscTxAPRx | Always | controls writing to the AP console |
| UartGscRxECTx | Always | controls reading from the EC console |
| UartGscTxECRx | IfOpened | controls writing to the EC console |
| FlashAP | IfOpened | controls flashing the AP |
| FlashEC | IfOpened | controls flashing the EC |
| OverrideWP | IfOpened | controls controlling write protect |
| RebootECAP | IfOpened | controls rebooting the EC/AP from the cr50 console |
| GscFullConsole | IfOpened | controls access to restricted Cr50 console commands |
| UnlockNoReboot | Always | controls unlocking Cr50 without rebooting the AP |
| UnlockNoShortPP | Always | controls unlocking Cr50 without physical presence |
| OpenNoTPMWipe | IfOpened | controls opening Cr50 without wiping the TPM |
| OpenNoLongPP | IfOpened | controls opening Cr50 without physical presence |
| BatteryBypassPP | Always | controls opening cr50 without physical presence and dev mode if the battery is removed |
| UpdateNoTPMWipe | Always | controls updating cr50 without wiping the TPM |
| I2C | IfOpened | controls access to the I2C master (used for measuring power) |
| FlashRead | Always | controls dumping a hash of the AP or EC flash |
| OpenNoDevMode | IfOpened | controls opening cr50 without dev mode |
| OpenFromUSB | IfOpened | controls opening cr50 from USB |
Some basic CCD functionality is accessible by default. There is read-only access to the EC console and read-write access to the AP console. There are some basic cr50 console commands you can run.
Cr50 CCD needs to be opened to access all CCD functionality or to modify capability settings so the device doesn't need to be open to access CCD functionality.
Use the general setup instructions to connect Suzy-Q and access the Cr50 console. The Cr50 console will be the lowest /dev/ttyUSB* device created by Cr50 or /dev/google/<device name>/serial/Shell
Modify capabilities to make it easier to open cr50 or access necessary capabilities - this step is optional, but the open state will be lost if cr50 reboots or the device loses power. If your use of CCD will possibly brick the device, it is recommended you modify the capability settings or set a ccd password, so you can reopen the device.
Use CCD
The first cr50 image with CCD support was 0.3.9. If you are not running 0.3.9, you need to download the image and update cr50 from the AP or using Suzy-Q. https://storage.googleapis.com/chromeos-localmirror/distfiles/cr50.r0.0.10.w0.3.9.tbz2
You can download the cr50 image and then flash cr50 using Suzy-Q from the chroot
from chroot > sudo gsctool cr50.r0.0.10.w0.3.9/cr50.bin.prod
If you are only briefly using ccd and aren’t doing anything that may brick the device, you can probably just stick to opening cr50. The open state will be lost after cr50 reboot. If you don’t want to have to reopen cr50, you may want to setup the ccd capabilities so you can use them without needing cr50 to be open.
If your device can boot, you can open Cr50 by entering dev mode and then sending the ccd open command from the kernel.
Entering dev mode has to be done manually. Using the gbb flags to force dev mode will not work.
First, on a root shell on the device, check the force dev mode flag isn’t set GBB flags by running. If you can’t access the shell, because you aren’t in dev mode, then you’re fine. You can skip steps 1, 2, and 3.
AP > /usr/share/vboot/bin/get_gbb_flags.sh
Clear 0x8 from the GBB flags and set the new value
AP > /usr/share/vboot/bin/set_gbb_flags.sh $OLD_FLAG_VALUE & ~0x8
Reboot the device
Put the device into recovery mode
dut-control power_state:recEnable developer mode
Verify Cr50 knows the device is in dev mode. The TPM state will print dev_mode if cr50 knows the device is in dev mode. If it doesn’t say dev_mode, ccd open will fail. If you see “TPM: dev_mode” you are okay to CCD open now. If you don’t see TPM: dev_mode, recheck the gbb flags to make sure they aren’t forcing dev mode. Retry the manual entry of dev mode.
cr50 > ccd
State: Locked
Password: none
Flags: 0x000001
Capabilities: 0000000000000000
UartGscRxAPTx Y 0=Default (Always)
UartGscTxAPRx Y 0=Default (Always)
UartGscRxECTx Y 0=Default (Always)
UartGscTxECRx - 0=Default (IfOpened)
FlashAP - 0=Default (IfOpened)
FlashEC - 0=Default (IfOpened)
OverrideWP - 0=Default (IfOpened)
RebootECAP - 0=Default (IfOpened)
GscFullConsole - 0=Default (IfOpened)
UnlockNoReboot Y 0=Default (Always)
UnlockNoShortPP Y 0=Default (Always)
OpenNoTPMWipe - 0=Default (IfOpened)
OpenNoLongPP - 0=Default (IfOpened)
BatteryBypassPP Y 0=Default (Always)
UpdateNoTPMWipe Y 0=Default (Always)
I2C - 0=Default (IfOpened)
FlashRead Y 0=Default (Always)
OpenNoDevMode - 0=Default (IfOpened)
OpenFromUSB - 0=Default (IfOpened)
TPM: dev_mode <==== This is the important part
Use 'ccd help' to print subcommands
You can start the open process from the AP. Once you start the process, you will need to press the power button when prompted open cr50.
Start the ccd open process from the AP.
AP shell > gsctool -a -o
Over the next 5 minutes you will be prompted to tap the power button.
After the process is finished, use ‘ccd’ on the cr50 console to verify the state is open
The Open setting will be lost whenever cr50 reboots. Make sure to setup ccd so you will be able to recover the device even if Open is lost. To open cr50 you need access to the AP. If your debugging will make the AP inaccessible and you want to ensure that you can recover the device, you either need to modify the capability settings so you can access the capabilities necessary to recover the device while cr50 is locked or you need to modify the capabilities so you don't need the AP to open cr50.
If you need to reflash the AP or EC, you can set the FlashEC or FlashAP capabilities to Always.
If you want to be able to open cr50 without the AP, set OpenNoDevMode and OpenFromUSB to Always.
If you can’t boot the device, you won’t be able to enter dev mode and send the open command from the AP. You will need to follow some non-standard methods to open the device. If you have enabled ccd before, cr50 may be configured in a way that you can still open cr50. If you haven't setup CCD before, you will need to remove the battery to enable CCD.
If you can remove the battery, you can bypass the AP command/dev mode requirements. ccd open is allowed from the console if FWMP doesn’t disable ccd and the battery is disconnected. This is the most universal method and will work even if you haven’t enabled ccd before. Some devices are glued shut if you can’t/don’t want to unglue your device do not rely on this method. Setup ccd correctly before flashing the AP/EC.
Disconnect the battery
Send ‘ccd open’ from the cr50 console.
You can check if testlab is enabled cr50 from the console.
cr50 > ccd testlab
CCD test lab mode enabled
If it’s enabled, you can open cr50 from the console without physical presence.
cr50 > ccd testlab open
This requires >=0.3.10. If these capabilities are set, you will be able to open cr50 from the console without dev mode.
cr50 > ccd open
You can run ccd open with the password to open from the console.
cr50 > ccd open $PASSWORD
Cr50 capabilities allow you to configure CCD to restrict or open the device as much as you want. You can use the ccd command to check and modify the capabilities. Cr50 has to be open to change the capabilities. Setting capabilities you want to use to Always will make them accessible even if cr50 loses the open state. If you are using capabilities that may cause cr50 to reboot or may brick the device, you should set the capabilities needed to recover the device to Always or setup the capabilities so you can open cr50 without booting the device.
Basic ccd functionality is covered by UartGscTxECRx, UartGscRxECTx, UartGscTxAPRx, UartGscRxAPTx, FlashAP, FlashEC, OverrideWP, and GscFullConsole.
You can go through the capability descriptions and figure out which ccd capabilities you want to use. After you figure that out you can modify the capabilities to Always be accessible.
> ccd set $CAP $REQ
For example if the EC console needs to be read-write even when Cr50 is locked set the capability to Always.
> ccd set UartGscTxECRx Always
If you want to restrict capabilities more you can set them to IfOpened. If you don’t want the AP/EC uart to be accessible at all when cr50 is locked, you can set them all to IfOpened.
Restrict EC
> ccd set UartGscTxECRx IfOpened > ccd set UartGscRxECTx IfOpened
Restrict AP
> ccd set UartGscTxAPRx IfOpened > ccd set UartGscRxAPTx IfOpened
If you want things as accessible as possible and want all capabilities to be Always, you can run
> ccd reset factory
This will also permanently disable write protect. To reset write protect run
> wp follow_batt_pres atboot
To reset capabilities to Default run
> ccd reset
By default Cr50 requires enabling dev mode before you can open the device and the open command has to be sent from the AP. You can change the capabilities to remove these requirements if you think your development may prevent the device from booting. You can also set the ccd password to get around these requirements. These options offer different pros and cons. You can decide which is best for you.
After opening cr50, you can set these capabilities to reduce the restrictions required to open cr50.
> ccd set OpenFromUSB Always > ccd set OpenNoDevMode Always
A ccd password can also be used to get around the open restrictions. The password will be required to reopen or unlock cr50, so keep track of the password. It can't be reset unless cr50 is open, so if you forget it, nothing can be done to reopen cr50.
Run the gsctool command and enter the password when prompted. It will prompt for the password twice.
from ap shell > gsctool -a -P
You can use the ccd command to check if the password is set.
cr50 > ccd
...
Password: [none|set]
...
You can clear the password by opening cr50 and then running the gsctool command agatin. When prompted for the password enter clear:$PASSWORD at both prompts.
You can also use the cr50 ccd reset command when cr50 is open. This will clear the password and reset all ccd capabilities to default.
After the password has been set you can use it to run ccd commands from the cr50 console.
cr50 > ccd open $PASSWORD cr50 > ccd unlock $PASSWORD
You can use it from the AP shell
cr50 > gsctool -a -o cr50 > gsctool -a -u
enter the password when prompted
Cr50 only enables ccd when it detects a debug accessory is connected. It detects the cable based on the voltages on the CC lines. If you are flashing the EC and AP, these cc voltages may become unreliable for detecting a debug accessory. You can use a cr50 command to tell cr50 to ignore the voltages on these cc lines and just keep ccd enabled. There are many things that could interfere with rdd, so it’s probably best to run this before doing anything else using ccd.
cr50 > rddkeepalive enable
This command is useful for making sure ccd stays enabled during debugging. It will increase cr50 power a lot when the debug cable is disconnected. If you’re worried about that, disable rddkeepalive when you're not using ccd.
cr50 > rddkeepalive disable
Cr50 presents 3 consoles through CCD. It has the AP, EC, and Cr50 console. The AP and EC consoles can be restricted using the 4 ccd uart capabilities UartGscRxAPTx, UartGscTxAPRx, UartGscRxECTx, UartGscTxECRx. The default setup is the AP is read write. The EC is read only. Cr50 console input/output can’t be suppressed. You can only use the GscFullConsole capability to enable restricted console commands.
Cr50 will create 3 /dev/ttyUSBX devices. They’re the cr50, AP, and EC console. The cr50 console normally has the lowest number. The AP and EC are the other two. You can figure out which one is which by pressing the power button or rebooting the device and looking at the uart output. If you have a bunch of devices, you can unplug suzyq and see which devices disappear to figure out the relevant ones.
Servo can also figure this out for you. You can start servo like you normally do
chroot > sudo servod -b $BOARD
After starting servo, you can use dut-control to get the consoles
chroot > dut-control cr50_uart_pty ec_uart_pty cpu_uart_pty
This is restricted by the FlashEC capability. This must be accessible to flash the EC.
The steps to flash the EC differ a lot based on what board you’re using. You should stick to using flash_ec to handle flashing the ec, because the steps can get pretty complicated and are board specific.
You will need to start servod then flash_ec will handle sending the correct cr50 console commands and updating the EC.
chroot > sudo servod -b $BOARD chroot > ~/trunk/src/platform/ec/util/flash_ec -i $IMAGE -b $BOARD
This is restricted by the FlashAP capability. This must be accessible to flash the AP.
Flashing the AP is standard across boards.
chroot > sudo flashrom -p raiden_debug_spi:target=AP -w $IMAGE
If you have a lot of ccd devices plugged in, you may want to use the cr50 serialname. You can get this by running
chroot > lsusb -vd 18d1:5014 | grep iSer
You can add the serialname to the flashrom command using
chroot > sudo flashrom -p raiden_debug_spi:target=AP,serial=$SERIAL -w $IMAGE
If you don’t see cr50 print any messages when you’re running the flashrom command, you probably need to use the serialname.
This is restricted by the OverrideWP capability. If this capability is accessible, you can use the cr50 wp command. If it's not, you can only control write protect using battery presence.
You can use the cr50 console command to change the write protect settings.
There are three write protect settings: forced enabled, forced disabled, follow_batt_pres.
follow_batt_pres - DEFAULT SETTING - use battery presence to determine the write protect setting. If the battery is connected, enable write protect. If the battery is disconnected, disable write protect. If the board doesn’t have a battery, then normally a screw is used. If the screw is present, enable wp. If it’s not, disable wp.
enabled - enable write protect no matter the state of the battery. Protect things like the AP/EC flash and various other components that use this write protect signal
disabled - write protect is deasserted no matter the state of the battery. You’ll be able to modify things like AP RO
You can set these from the cr50 console
cr50 > wp [enable|disable|follow_batt_pres]
This setting will persist until it is cleared using the wp command or until cr50 reboots/loses power. After these resets, cr50 will default to the atboot setting. The default setting is follow_batt_pres, so cr50 will go back to following battery presence after reboot unless the atboot setting has been overridden.
Using the atboot arg will update the current and atboot wp state. If the atboot arg is given to the wp command, then the setting will persist until it is cleared by the wp command. It won’t be reset by anything else, so if you only want to disable/enable write protect for a short time, make sure atboot is set to follow_batt_pres. If you want to permanently disable or enable write protect and want to ignore the battery, this is a good setting to update.
cr50 > wp [enable|disable|follow_batt_pres]
You can use the wp command to get the write protect state even if the capability is restricted.
cr50 > wp
Flash WP: [forced ]enabled|disabled
atboot: forced enabled | force disabled | follow_batt_pres
Gsctool also supports getting the write protect state
AP > gsctool -a -W
The output will show the current and atboot setting.
The current wp setting will not explicitly show that write protect is currently following battery presence. You have to get this by checking if the wp state is ‘forced’ enabled/disabled. Forced means write protect is being overridden by the console command. If it just shows the state without forced, write protect is following battery presence.
The atboot setting shows what the wp state will reset to after reboot.
If the OverriedWP command isn’t accessible, you can use battery presence to change the wp state as long as the wp setting is still follow_batt_pres.
wp disable - disconnect the battery
wp enable - connect the battery
If the wp setting has been overridden by ccd, this won’t work until the current wp setting is reset to follow_batt_pres
cr50 > wp follow_batt_pres atboot
Chromeboxes do not have batteries, so cr50 can't use battery presence for write protect. They use a write protect screw. You need to remove the write protect screw to disable write protect if cr50 is set to follow_batt_pres.
Bob‘s have a write protect screw in addition to battery presence. The write protect screw will force enable write protect until it’s removed. If cr50 is set to follow_batt_pres, you need to remove the write protect screw and disconnect the battery to disable write protect. If you run wp disable, you will also need to remove the screw.
Once cr50 is open and all capabilities have been set to Always, cr50 should be able to be used as a servo replacement. It has all of the capabilities servo does and support has been added to hdctools to convert servo controls to cr50 and ec console commands.
If you start servod and select the ccd device, you should be able to use servo dut-control comands normally.
chroot > sudo servod -b $BOARD
If cr50 reboots or usb disconnects for some reason, servod will lose the connection to the cr50 usb. Support has just been added to hdctools to reinitialize all of the servo ccd interfaces, so things should come back up after the disconnect, but it might still have bugs.
Servo can take care of a lot of the less intuitive things for you like during init it will send rddkeepalive enable. It will also find the AP, EC, and Cr50 uart. Servod knows how to interact with the i2c endpoint, so you can use servod to read power from the INAs if they’re populated.
Suzyq doesn’t have all of the necessary things to replace servo for FAFT, but you should be able to use it for normal debugging functionality. You will need a type c servo v4 for ccd if you need to run FAFT.