thank a lot , this is want I want. Btw how to do make this output fixed 5v ?the default output seems adjustable .So, I also manage to modify one of these switches
Thanks mpogr for sharing your knowledge!
The one thing that really pissed me off was how noisy these little things are!
Instead of buying new low speed fans which would be just as expensive as the switch, I decided I would have to use the Fans that came with it. I did a lot of experiments and I came up with a solution to keep them quiet without modifying the switch irreversibly. So in order to keep them quiet I decided to lower their voltage thus making them spin slower. A 5 volt linear regulator could do the job except that it would get very hot, and switched regulators are usually big (compared with a 7805).
But then I found these on ebay:
10pcs DC-DC 12-24V To 5V 3A Mini Step Down Module Buck Converter Adjustable | eBay
These small PCB's are cheap as beans and they are the same size as a 7805 plus they allow for variable output (which allows for tuning fan speed to almost any noise desired). I striped 4 noctua NA-RC7 low-noise adapters I had (they are useless with these switches by the way...) and made 4 adapters of them. The small PCB's have a potentiometer that allows to change output voltage. 5V seems to be a good ratio between noise/speed that will allow the switch to operate safelly if you are not going to use it with 12 ports on all the time at full speed.
I'm getting temps bellow 40ºC on all boards except CPU Board Monitor 2 which is at 52ºC. This is with 4 passive DACs and one QSFP+ adapter connected. PWM and Tacometer will work as well with this mod (although PWM will not make fan speed change a lot at low voltages). Also the switch will complain (you will get an alarm) of low Fan speed. Haven't figured a way of getting rid of this, but it doesn't bother me at all.
Anyway, just decided to share this, since it might be usefull to someone. Please use this with care, reducing FAN speeds to very low speed/air flow can kill the switch.
PS: the voltage regulators have an enable pin whitch should be left floating.
PPS: also another nice thing about this is that power consumption drops by almost 20W, making this switch running at arround 30W... that's insane for the speeds this thing can do.
-Edit- correction regarding Enable pin on these devices.
Yeah , if you find a way to modify it , maybe also could set fan speed, this from config.ini for fan controlI used flint to pull the config from the current firmware image .bins for the SX6018 and the SX6012 which is how I learned that the magic entry is "module_power_level_supported=5". My problem now is how to either load an updated config into the switch or to modify the firmware with a new config.
As far as I can tell the only way to modify a firmware is to generate a new one using mlxburn and that requires an .mlx source firmware file, which I don't have. I have not seen any tool which will burn just the config.
It seems Mellanox used to publish firmware sources (.mlx files) on their website, at least for adapter cards, until just a couple of years ago.