DS280DF810: EOM monitor issue

Hi Mizobuchi-san,

Regarding the EOM Reading 0 Issue:

Given that EOM monitor is 0 and that a communication error or link down occurs, this seems to suggest that the retimer is not getting CDR lock.  Have you checked the CDR lock status in this condition?  Would it be possible to share a register dump in this state where 0x27/28 read 0 and also your device configuration sequence?

Regarding the EOM Update Issue:

How frequently are you reading 0x27/0x28?

There is an option to force an EOM update.  Could you try writing the sequence below?

ch_reg_0x23[7] = 1; // Enable override for HEO/VEO trigger

ch_reg_0x24[1] = 1; // Trigger HEO/VEO measurement

Thanks,

Drew

Hi Drew-san

Thank you for your reply.

We will check your advice.

Thanks,

K. Mizobuchi

Hi Drew-san

Drew Miller1 said:

Have you checked the CDR lock status in this condition?

=>Yes,  In case of  link down state, register values are 0x27=00, 0x28=00, 0x29=00,  0x78=30. 

Drew Miller1 said:

Would it be possible to share a register dump in this state where 0x27/28 read 0 and also your device configuration sequence?

=> What registers do you want to check ?

=> your device configuration sequence is below,

//Disable CAL_CLK_Out
debug i2c write 0 0x19 0xff 0x00
debug i2c write 0 0x19 0x0a 0x01

//setting channel Reg.
debug i2c write 0 0x19 0xfc 0x01
debug i2c write 0 0x19 0xff 0x03
debug i2c write 0 0x19 0x00 0x04
debug i2c write 0 0x19 0x0a 0x0c
debug i2c write 0 0x19 0x2f 0x50
debug i2c write 0 0x19 0x3d 0x0a

//disable HEO/VEO
debug i2c write 0 0x19 0x67 0x00

//ch 6/4/2/0 open CDR
debug i2c write 0 0x19 0xff 0x01
debug i2c write 0 0x19 0xfc 0x55
debug i2c write 0 0x19 0x0a 0x00

//CH 7/5/3/1 power down driver,disable SD, PFD, CDR
debug i2c write 0 0x19 0xff 0x01
debug i2c write 0 0x19 0xfc 0xaa
debug i2c write 0 0x19 0x15 0x18
debug i2c write 0 0x19 0x1e 0xec
debug i2c write 0 0x19 0x14 0x44
debug i2c write 0 0x19 0x13 0xf0

Drew Miller1 said:

How frequently are you reading 0x27/0x28?

=> It is manual reading, so every few seconds.

Drew Miller1 said:

There is an option to force an EOM update.  Could you try writing the sequence below?

ch_reg_0x23[7] = 1; // Enable override for HEO/VEO trigger

ch_reg_0x24[1] = 1; // Trigger HEO/VEO measurement

=> Is "ch_reg_0x24[1]= 1 " read register ?

=>We could not update EOM monitor by above sequence.

Best Regards,

K.Mizobuchi

Hi Mizobuchi-san,

Thanks for sharing your configuration.  Could you share some background on why you're disabling the HEO/VEO lock monitoring?  I believe this is contributing to you reading back a HEO/VEO of 0.

I was able to reproduce some similar behavior on the bench, but with the HEO/VEO lock monitoring disabled, I wasn't able to identify a manual override.

K.MIZOBUCHI said:

Is "ch_reg_0x24[1]= 1 " read register ?

It is documented as a read register, but the description for it seemed to suggest that it would be used to trigger a HEO/VEO measurement.  Based on this, I was wondering if the "read" description might be an error.  However, I tried testing this sequence in lab today and also found that it did not update EOM monitor.

Thanks,

Drew

Hi Drew-san

Drew Miller1 said:

Could you share some background on why you're disabling the HEO/VEO lock monitoring?

=> We thought this was an unnecessary feature when making it into a product.

And this is because we want to reduce power consumption as much as possible.

Even if HEO/VEO lock monitoring is disabled, we can usually see EOM monitor only once. But can not be updated.

Drew Miller1 said:

I believe this is contributing to you reading back a HEO/VEO of 0.

=>We changed HEO/VEO lock monitoring to be enabled, but we found that it did not update EOM monitor.

Can you see the EOM monitor updated in your lab ? If so, could you tell us the sequence ?

And  are there any problem if EOM monitor is disabled ?

Thanks,

K. Mizobuchi

Hi Mizobuchi-san,

K.MIZOBUCHI said:

=>We changed HEO/VEO lock monitoring to be enabled, but we found that it did not update EOM monitor.

I see the EOM monitor update in lab when HEO/VEO lock monitoring is disabled.

However, in the case where HEO/VEO lock monitoring was disabled and registers 0x27/28 read back 0, re-enabling the HEO/VEO lock monitoring does not resolve the issue.

When you are testing with HEO/VEO lock monitoring enabled, are you just getting a single value and then find that it does not change?  How much do you expect it to change?  Are you changing the input signal to the retimer?

K.MIZOBUCHI said:

And  are there any problem if EOM monitor is disabled ?

The HEO/VEO lock monitor is used to see if the retimer should re-adapt to the input signal (in the event that input signal quality changes).  I wouldn't expect any issues with disabling the EOM monitor if the input signal quality is expected to be constant.

Thanks,

Drew

Hi Drew-san

Drew Miller1 said:

I see the EOM monitor update in lab when HEO/VEO lock monitoring is disabled.

=>We understood that basically, EOM monitor disabled and EOM monitor update are not related.

Drew Miller1 said:

When you are testing with HEO/VEO lock monitoring enabled, are you just getting a single value and then find that it does not change?  How much do you expect it to change?  Are you changing the input signal to the retimer?

=>Yes, The value was not updated whether we changed the input signal level to the retimer or not.

We will consider it again.

Thanks,

K.Mizobuchi

Hi Drew-san

We tried to test again. As the results,

when HEO/VEO lock monitoring is enabled, we confirmed that EOM monitor can update by changing input signal level.

when HEO/VEO lock monitoring is disabled, we confirmed that EOM monitor can not update by changing input signal level.

We have questions below,

What is the resolution of the EOM monitor?

Where is the EOM monitor placed in the circuit block?

Is it possible for the EOM monitor to become 0 if the input amplitude to the retimer is small not 0 ?

Thanks,

K. Mizobuchi