Margin Analysis for the phyCAM-L Interface
This article describes how to use the Margin Analysis Tool to check the signal quality on a phyCAM-L coaxial connection.
The signal quality in the final system depends on several factors, e.g. the properties and length of the coaxial cable used and the power transmitted over the cable to supply the camera head with any peripherals.
With the result of the tool, you can estimate how good the quality of the signal transmission on the phyCAM-L link is and whether it meets the requirements of FPD-Link III for interference-free transmission.
The phyCAM-L Margin Analysis Tool is based on the Application Note "SNLA301" from Texas Instruments and on the evaluation of an eye diagram.The phyCAM-L Margin Analysis Tool is based on the application note "SNLA301" from Texas Instruments. The user can use it to determine the signal quality of the digital data transmission of an individual coaxial link with their phyCAM-L system.
In the following description, we assume that the converter module VZ-018 (phyCAM-L to phyCAM-M - Bridge) is used for the connection of the phyCAM-L - camera.
Of course, you can also use the tool accordingly for checking systems in which the FPD-Link III - Deserializer is integrated on the baseboard or single-board computer (SBC).
The use of this tool requires a Python3 capable system with the SMBUS library.
The tool is currently (as of Q1/2022) available for boards with i.MX 8M plus processor.
The VZ-018 module is connected to the baseboard via the phyCAM-M interface. The coaxial cable to be tested is connected to Port 0 of the VZ-018 module. The end of the coaxial cable is connected to the phyCAM-L module.
Press the reset button on the VZ-018 and reset the module.
The tool is operated via the terminal/command line:
First, enter the I2C BUS address of the phyCAM-L interface.
There are several modes and required values that can be optionally adjusted.
Before starting the Margin Analysis test, you can perform a final digital reset including the registers. This includes the previously configured GPIOs on the camera module used.
For the result to be as practical as possible, the camera should be working. A digital reset deactivates the camera if necessary (see PHYTEC Application Note LAN-106).
It should be noted that TI specifies that the sensor must not operate during the MAP test.However, it is also recommended that the camera should be working so that the power consumption over the PoC line can also be included in the consideration of the MAP test. Since the MIPI CSI-2 input of the serializer cannot be disabled, according to the current status, the following workaround can be applied here. If the number of CSI-2 data lanes is configured incorrectly, the serializer apparently does not process the CSI-2 data. The sensor can thus be brought into the near-series operating state and the FPD-Link 3 is operated as suggested by TI.
However, PHYTEC recommends the correct operating condition including the CSI-2 configuration, as this is the only way to obtain reliable results.
Choose a colored or black and white map output. The graphical diagram can be displayed in color as well as in gas levels.
When called via the USB interface via minicom, color and graphical errors occur because minicom does not support UTF-8 and the special characters used are in Extended ASCII.
Dwell time until the next map area of the eye diagram (EQ/Strobe position) is checked. The default time is 0.9 seconds.
The system requires a certain time until it works stably. A longer dwell time means that the first communication is more reliable.
The number of times an EQ/Strobe position (a box) is sampled in succession. 10 times is the default value.
The time between initialization and evaluation of an EQ/Strobe position during a run (lock runs), in which the number of signal errors are determined. The default time is 0.1 seconds.
Strobe / EQ Position
The scanning range can be limited. To avoid scanning the entire eye, the scanning range can be limited horizontally and vertically. For this purpose, the lines and columns within this range are specified.
The eye does not have to be scanned completely if the ideal range is roughly known (save time = faster result).
Enter integer values from 0 to 14 :
Strobe Position Begin:
Strobe Position End:
current Strobe Position Begin: 5
current Strobe Position End: 13
Enter integer values from 0 to 14 :
EQ Position Begin:
EQ Position End:
current EQ Position Begin: 1
current EQ Position End: 11
Shifting of the sampling range due to clock and data delay.
No clock and database delay:
with clock and database delay:
- strobe positions 6 and 8 are further away from 7
- larger sampling range up to the edge of the eye diagram
The map maps the lock status, parity errors, forward channel CRC errors, forward channel sequencing errors, and forward channel encoding errors [...] across all EQ settings and strobe positions [...]. The green squares indicate successful operating states where the deserializer and serializer are locked with zero errors.EQ levels with at least four continuous strobe positions are considered recommended EQ levels. TI generally recommends having a range of at least three EQ levels with four continuous strobe positions, including a contiguous rectangle of pass states that has two EQ levels times four strobe positions.
In the terminal, there is both a graphical and a percentage output in 10 percentage steps of the sampling process. The lower the percentage of an EQ/strobe position, the more errors have occurred at that point.
Definition of colors related to signal quality:
- GREEN = 100%
- YELLOW = 10% - 90%
- RED = 0%
The evaluation and summary of the parameter settings are stored in the ma_lock_result.txt file. After finishing the run, the user can save this file locally and then convert it into an Excel file.