Other peripherals
TPM
The TPM provides cryptographic functions to ensure the hardware identity and integrity of the unit. It contains unique keys and includes certificates from the manufacturer and custom certificates for verifying authenticity of the unit.
| Path in the OS | /run/unipi-plc/by-sys/tpm/dev |
TPM technical parameters
| TPM version | Trusted Platform Module 2.0 |
| Manufacturer | Infineon |
| Model | OPTIGA SLB 9672 |
| Bus | SPI (33 MHz) |
Retain
Retain memory is a fast non-volatile memory used for storing current values of chosen variables. It is separated from eMMC storage and thus do not reduce the lifespan of the main storage.
| Path in the OS | /run/unipi-plc/by-sys/retain/mem |
Retain technical parameters
| Memory size | 128 kB (default) |
| Memory type | NVRAM |
| Bus | SPI (30 MHz) |
| Model | MB85RS1MT |
| Lifespan | 1013 times / byte |
RTC
RTC (Real-time clock) can keep track of elapsed time, even when the device is powered off or is not connected to internet.
| Path in the OS | /dev/rtc |
RTC technical parameters
| Battery | CR2032 lithium battery |
| Bus | I2C |
| Model | MCP79410 |
| Lifetime | approx. 10 years |
Hardware Watchdog
Hardware watchdog checks for periodic pulses on WDG pin (GPIO27) and reboots the devices by cutting off the power supply if no pulse is detected within 10 second window. It is possible the reboot happens somewhere between Tmin=10 sec and Tmax=20 sec after last pulse, because the check is a the end of fixed 10 second window (see image). The intervals cannot be normally changed. Hardware watchdog is inactive until it is activated by first pulse.
Automatic pulse generation on WDG pin is by default enabled in firmware. First pulses are generated by uboot boot loader, after that the pulse generation is left to systemd daemon. If both kernel and systemd are running, then systemd generates one pulse every 4 seconds. Systemd can be configured to watch multiple application at once. When the application is not sending messages to systemd, it can be set up to reset the application in such case. More information can be found in the systemd documentation. This automatic safeguard using systemd can be disabled for customers in customized image and for this special case the functionality is passed to user application. We recommend to have this functionality enabled for critical applications.
Note:
Dedicated watchdog and Master watchdog (MWD) are two separate systems!
While dedicated watchdog monitors if the operating system is running correctly, the MWD is present only for variants with I/O and monitors communication with I/O subsystems.
Cold reboot
The device can cold reboot itself with pin GPIO26. When this pin is set to log. 1 for at least 1 ms, then all power supplies in the device are cut off for at least 50 ms, which reboots the compute module and all peripheral.
In standard OS this process is done automatically after calling poweroff or reboot command at appropriate moment. Both command will cause a cold reboot of the device.
User or any application with correct rights can use this HW feature.
Attention:
In standard SW the unit cannot be turned off, go to sleep/hibernation or switched to low power mode, but only rebooted.
Service button
Input device emulating the ENTER key. It is also used to access the service mode.
| Path in the OS | /dev/input/event0 |
ULED
User programmable LEDs which can be set to indicate any event or state. They can be controlled from the user program or directly from OS.
| Path in the OS | /run/unipi-plc/by-sys/ULEDx/brightness |
Note:
Replace x with ULED number.
| Color | Green |
| Off value | 0 |
| On value | 1 (or any other than 0) |
Attention:
When reading ULED from Modbus registers mind that this value is cached (together with ULED coils). Avoid using Modbus and sysfs together to read/write ULEDs, otherwise the Modbus can return incorrect values.
