From the OCP-TAP & Timebeat team comes the best timing and positioning module for the Raspberry PI CM4!
It's made by the same team who contributed the IEEE1588 capability for the BCM54210PE Ethernet controller in the CM4 to the Linux kernel in collaboration with Raspberry Pi and Broadcom.
This module "sandwiches" in between the IO board and CM4 and has expansion slots to extend functionality and performance at a fraction of the cost of a dedicated timing appliance.
This guide details the functionality of the TImeCard mini in detail.
For details on installing the TimeCard mini into the CM4 IO unit read this guide
- ANT: fl IPEX-1 connector for connecting GNSS antenna input.
- 10 Mhz: fl IPEX-1 connector for connecting stable frequency input to GNSS module
- PPS OUT: fl IPEX-1 connector for connecting 1PPS output from GNSS module
- PPS IN : fl IPEX-1 connector for connecting 1PPS input to GNSS module
- 100 Pin top: Direct connection for the CM4 unit or riser board
- 100 pin bottom: Direct connection to click straight onto a CM4 IO board or power board
- Module A & B Hirose connectors: used to connect to Timebeat expansion modules
- Dip Switch: used to manage the input/output configuration of the PPS Net.
This module is created with a central net we refer to as the PPS Net.
The PPS Net is the baseline for how the module is configured in relation to the various input and output options.
To explain this in more detail below shows the mappings of the LEA and MAX Ublox chips.
The Timepulse pin (Pin 4 on the MAX and Pin 28 on the LEA) is able to send 1PPS to ETH_SYNC on the CM4 unit provided that the GNSS IN and ETH OUT positions on the dip switch are set to on.
The Dip switch can be found just above the OCP-TAP logo on the right-hand side of the board (connector listed number 8).
The TimeCard mini has a default behavior of providing a 1PPS to the PPS OUT u.fl connector (connector labeled 3)
Positioning the Dip Switch setting for GNSS In to off and switching PPS_IN to on, the PPS Net will provide input from the PPS In connector (connector labeled 4) and not from the Ublox unit.
The PPS In connector (labeled 4) irrespective of being switched on or off with the Dip Switch the input signal still gets received by the EXTINT pins on the Ublox Unit (Pin 5 on the MAX and pin 27 on the LEA).
In providing the 1PPS to the EXTINT pin you can provide an external stability of measure phase using the EXTINT functionality of the Ublox module. This also means that you can utilise PPS IN and PPS OUT functionality concurrently.
Both modules LEA and MAX connect to serial0 UART interfaces in the CM4.
In addition, the I2C interfaces are routed to the relevant GPIO pins.
The above image details the connections for Module A and B. As the LEA modules allow for a second EXTINT pin we have connected the 10Mhz network of expansion module A and B to the LEA Ublox unit. This allows for the addition of external oscillators.
The external oscillators allow for a very stable PPS to be provided.
The expansion boards currently support the SiT5711 and SiT5721, these oscillators are industry-leading and can provide up to 5ppb stability. (currently, only the LEA option module supports external oscillators).
Other things of note include:
- External oscillator modules are always being added to the ecosystem to suit more budgets, currently being tested are oscillators in the 10-20ppb range.
- A “pro” version of the LEA-M8F without the module slots being developed.
- A power / USB board allowing the board to mate with a power/io board so it can be used in other projects without a CM4. This will be functional with all module models.
The expansion slot will contain other things than Oscillators. There will also be interesting things for monitoring and sync in the mobile network space… 30.720 MHz and multiples hereof for instance...