10-23-2018 07:18 PM
You can monitor/estimate the current of 0X1A by the Maxim PowerTool when one or two of SFP+ is enable/disable using RT_TX_DISABLE.
10-23-2018 07:35 PM
10-23-2018 07:43 PM
There are multiple methods.
Referring to UG1182, we see (in figure 3-26) that the SFP socket is powered from the UTIL_3V3 supply rail. That rail comes from a Maxim DC/DC controller that supports PMBus commands that (I believe) include the ability to read back output current. However, (see figure 3-44) the UTIL_3V3 rail supplies more than just the SFP socket, meaning you would need to somehow measure the current with the SFP unplugged, measure the current with the SFP plugged in, then subtract.
Referring to UG1182, we see (in figure 3-26) that the SFP socket is powered from the UTIL_3V3 supply rail via some inductors. You could use a multimeter to measure the DC resistance of those inductors (with the power off), then measure the voltage drop (with the power on) across the inductors and calculate the current (and hence the power) from that.
The SFP socket has an I2C interface to allow software to interrogate registers inside the SFP module. These registers are defined in SFF-8472. SFP modules don't actually measure their supply current or power consumption, but they do advertise a "power class" which describes the maximum power they will (supposedly) draw in the steady state. From SFF-8431, these are:
Power Level I modules - Up to 1.0W
Power Level II modules - Up to 1.5W
Power Level III modules - Up to 2.0W
10-23-2018 07:45 PM
10-23-2018 08:02 PM
10-23-2018 08:08 PM - edited 10-23-2018 08:10 PM
If you try the "voltage drop across the inductor" method, the accuracy will be limited by the resistance measurement. As the resistance will be quite low (I guess at about 10mohm, which is less than the resistance of multimeter leads), try to use a four-terminal resistance measurement which will be available on a desktop (rather than a handheld) multimeter.
Also, the inductor will use wire made of copper, which has a poor temperature coefficient of resistance. I suggest measuring the resistance both before and after measuring the voltage drop to avoid errors due to temperature changes.
10-23-2018 08:10 PM
Maxim power tool is not XPE, which is used to monitor current by PMBUS: