DP83TC812R-Q1: DP83TC812R SQI Monitoring

Hi Annamalai,

The SQI before cable plug out is very good. After the plug out and plug in, looks like link is down. You can do a soft reset 0x001F = 0x4000 and reinitiate the link-up. You can monitor SQI after that.

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Regards,
Gokul.

HI Gokul,

1) In one of my HW the SQI is always 0, what could be the reason (This is a different problem though) ?

2) Just doing a soft reset of the PHY is enough or I need to do perform the complete register init sequence (does it also modify some other registers) ?

Regards,

Annamalai

Hi Annamalai,

You can check for the link status on that HW and check if the device is linked-up. If not, we can look into why it is not linked up.

There is no need to perform register init sequence after soft reset as registers are not reset.

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Regards,
Gokul.

HI Gokul,

Thanks for your prompt answer it answered my point 2, 

I still need answer for point one. above where the PHY is working fine, pings etc.. but SQI is still 0

Regards

Annamalai

If you know and can provide some pointers on 1) let me know

Hi Annamalai,

Can you please provide the read values of registers 0x0001, 0x0871, 0x0A85, 0x0A88?

You can use indirect register access as you mentioned above to read these registers.

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Regards,
Gokul.

All read via extended access (0x1F)

0x0871: 0x0

0x0001: 0x61

0x0A85: 0x3e

0x0A88: 0x2d22

It is strange after i read these 3 registers, now the SQI is good!

Not sure why I just used to read 0x01 without extended read.

so you recommend reading all 3 registers for link status check? Now it looked the SQI register is back stable and recovered from kind of a lock.

Why should i use Extended read for reading 0x01 ?, what are these 2 registers 0x0A85 , 0x0A88 ?

Must I read them every time to get SQI or when link is UP?

Should I always use Extended Reads/Writes?

Do I need to always use Extended Read/Writes for this PHY for a stable operation? even after directly its power up ?

HI Gokul,

Could you please answer above?

Regards

Annamalai

Hi Annamalai,

Registers 0x0A85, 0xA88 are internal signal processing registers. I have asked you to read them to get some information on link stability and also to check if the extended read/write is going on properly.

You need not read these registers every time.

Can you please read register 0x871 multiple times and let me know the values? I am not sure why the value is not as expected when read the first time.

Register 0x0001 can be read through direct method and doesn't be read using indirect method. 0x871 should be read using indirect method.

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Regards,
Gokul.

Yes (the values are given above), but strangely after the first read of the registers you mentioned the SQI read got recovered and it gives a proper value. (not sure) how it got recovered !

now the read of 0x0871 is proper and it gives 0xcc

It is not the first time that it dint work, it stopped working at some point and never recovered. but now after the reads of register your mentioned it works.

Hi Annamalai,

Please let me know if you are able to recreate the issue. The value of 0xcc indicate that the SQI is 6 which is really good.

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Regards,
Gokul.

HI Gokul

I could not reproduce the issue any longer but i am concerned as i dont know how it got recovered after reading those registers in extended mode

Regards

Annamalai

Hi Annamalai,

The register reads have nothing to do with SQI recovery, They are status registers and will not impact any functionality.

You need not read these registers again when you recreate the issue. Please power cycle the board and try to read the SQI register after link-up.

My guess might be that the first time extended register reads were not going through properly, although you'll be a better person to guess why the value was different the first time.

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Regards,
Gokul.

HI Gokul

I could not reproduce this issue, but when I do a soft reset the SQI is 0xCC, otherwise now i am seeing in same board is 0xAA,

But doing a soft reset has a side effect, it causing the link to go down and then link up, i dont want this to happen. How can i avoid this ?

Regards

Annamalai

HI Gokul

You initially mentioned that soft reset to be done when link is down and make the link up again. What shall happen when  I do a test with cable manually unplugged and plugged back again?

If i unplug the cable then the link is down and when i connect the cable the link will be up again, so where shall i do a soft reset (during link down) ?

Link will be up only if the cable is connected back right

Btw this is my init sequence as per reference driver:

Regards

Annamalai

HI Gokul

As you initially suspected that Extended Reads were not working, actually SQI was returning 0, but other tests which use Extended reads were actually ok.

Now, also i am getting a wavering SQI like 0xaa, 0xcc, 0xee each time i power cycle or hotplug the eth cable on one of the target, but in other setup it worked ok.

Regards

Annamalai

Hi Annamalai,

You can cross correlate the init settings with the ones in the following app note https://www.ti.com/lit/an/snla389a/snla389a.pdf

The SQI value is toggling between 5,6,7 which is what we usually see. I don't see any risk in this.

Regarding, cable plug out and plug in, it is good if we do a soft reset after connecting the cable. Usually when hot plug-in and plug-out is done, the signals PHYs receives are usually indeterministic owing to signal bouncing and other effects. A soft reset sort of restarts the training and makes sure that the device links-up in a reliable way.

A soft reset causes a link-down and then link-up. There is no work-around for that.

Please let me know if you need more details.

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Regards,
Gokul.

This can some time cause cyclic link down and up, since we poll in the BMSR (reg 0x1) for link status. BMSR gets updated once when hotplug the cable, (w/o the reset), so you mean even if the BMSR shows link up, still we need to do soft reset and take care of this in design ?

Hi Annamalai,

If register 0x1 shows link status as up and if the SQI is good (>=3), then you need not do a soft reset.

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Regards,
Gokul.

HI Gokul

So if the link is up and SQI is < 3 , i need to do a soft reset ?, and I need to keep doing soft resets till the SQI >= 3, sorry your statements are confusing me

I still dont understand when / where i need to do soft reset, first time you told me to do a soft reset when link is up, now you saying to do a soft reset if sqi is also less than 3.

Regards

Annamalai

We are just using link up , link down by polling BMSR registers to determine if the cable is plugged out or plugged in