AM625: DDR configuration

Are you using DDR4 or LPDDR4?

If you configure the dtsi for <85C, and execute at these temps do you still experience the performance degradation?

Note that setting the operating temp >85C will increase the refresh rate 4x.  This increase in is required by the memory JEDEC specs to ensure the data contents are retained at higher temperatures.  The extra refresh commands may be pushing the total available bandwidth beyond 100%

What CPU usage do you experience at <85C?

Regards,

James

Are you using DDR4 or LPDDR4?

- DDR4

If you configure the dtsi for <85C, and execute at these temps do you still experience the performance degradation?

- <85C,the cpu idle is about 22%, which meets our performance requirements.

Hi Tom,

Ok, thanks for the info.  So it appears the 4x increased refresh rate is eating up the remaining 22% of idle headroom, which is why you are experiencing errors.  You will have to optimize your application to create more idle time with the <85C configuration.    

Are you configuring for 800MHz?    Can you provide the ISSI configuration file, there may be some opportunity to optimize timing, but ultimately i think you will need to check your application implementation and see if you can improve the cpu load.

Regards,

James

Hi JJD：

We want to check if TI can't support change the refresh rate of ddr for different temp ? Or only can use a fixed rate for all temp?

Hi JJD：

We want to use the DDR configuration for 85C which is generated by TI Sysconfig web.

But if the temp is over 95C, we want to change the DDR configuration in code to support 95C temp.

Could you please tell us how to change it? Which registers should change?

Thank you.

Tom,

tom zhang said:

We want to check if TI can't support change the refresh rate of ddr for different temp ? Or only can use a fixed rate for all temp?

Dynamic refresh rate is currently not supported, but is expected to be supported in a future SDK release.  You have to use a fixed rate for all temps, so you would have to fix it to the highest operating temp for your application

tom zhang said:

But if the temp is over 95C, we want to change the DDR configuration in code to support 95C temp.

Could you please tell us how to change it? Which registers should change?

You can change this in the tool using the Operating Temp parameter

Regards,

James

Hi JJD：

Only change this item? and keep other setting for -40C to 85C, it will support 95C or 105C automatically on software?

At first, we set this as -40C to 105C, and also change other timings to support -40C to 105C.

Yes, you only need to change this item.  When you change the temp range, it will automatically calculate and change other associated parameters, such as refresh rate and derating of other parameters.  Please check the README link in the tool for more information.

Regards,

James

Dear Tom.

wants to sync the status with you as below, is it right?

1. set to -40C to 85C, and the timing parameter related to refresh according to ISSI SPEC, the system loading is 78% in normal temperature environment, right?

2. set to -40C to 105C, and the timing parameter related to refresh according to ISSI SPEC, the system loading reach to 100% in normal temperature environment.

If it is right, would you please help provide below?

1. save the two configurations to local in two .syscfg files, and share in the ticket.

2. ISSI SPEC.

Please let us know if it can be uploaded here, or send me by email.

thanks a lot!

yong

Hi Yong：

For question 1 and 2, we both test it in normal temperature.

The ddr configurations for 85C,95C,105C, in attacment

ddr_configurations.zip

Hi JJD:

We changed this item, but some items which is generated automatically is not correct for my DDR. So we need to modify some items.

And we changed this item for 95C ,105Cm, then we modify some iteams, the configuration will cause CPU usage reach to 100%

Yes, this is most likely caused by the refresh rate increase.  Refresh rate needs to be increased according to JEDEC spec for high temp operation.  Since we don't support dynamic refresh rate, you have to choose the temp range to cover the highest temperature use case.  Thus the higher refresh rate will still be applied at the lower temps.

Regards,

James

Hi JJD:

Yes, we use the higher refresh rate for highest temperature. But in lower temps, the cpu rate reaches to 100%

We can't use the board because all programs run verfy slow.

As mentioned before :

You will have to optimize your application to create more idle time with the <85C configuration.    

Are you configuring for 800MHz?    Can you provide the ISSI configuration file, there may be some opportunity to optimize timing, but ultimately i think you will need to check your application implementation and see if you can improve the cpu load.

Regards,

James

Dear James.

yes, customer configured DDR4 for 800MHz.

would you please check the configuration files provided by customer in tom's post as below? 

tom zhang said:

Hi Yong：

For question 1 and 2, we both test it in normal temperature.

The ddr configurations for 85C,95C,105C, in attacment

ddr_configurations.zip

and one more point, would you please check if we can help this case from HOST perspective as it seems higher refresh rate leads to high loading.

tom zhang said:

Yes, we use the higher refresh rate for highest temperature. But in lower temps, the cpu rate reaches to 100%

We can't use the board because all programs run verfy slow.

also, they provided the ISSI DDR4 SPEC, please download it if necessary. I will give you one key by email.

43-46QR85120B-16256B.zip

thanks a lot!

yong

Hi yong,

can you try to enable TCR mode with extended temp range in the 95C configuration?

Based on the spec, the memory will adjust its internal refresh period, which should help the bandwidth issue by skipping unnecessary refresh cycles at lower temperatures.

You should see higher available bandwidth with 95C config than you do with 105C config.  

Note that this is not the case for 105C, the refresh rate will remain the same for internal and external.

Regards,

James

Dear Tom.

please help verify the suggestion from JJD ASAP and provide feedback.

And also, please note that TI only can support the analysis, but we don't know why it will increase bandwidth usage in normal temp when set to -40C to 105C.

thanks a lot!

yong

Hi JJD:

    The DDR vendor suggests to change these:

    LPASR mode:  Manual mode, Extended temp

    TCR mode: Enabled

   TCR range: Extended

   Are these right?

Hi JJD:

 Ok, we wil try these configs for 95C. Thank you
 Does this also for 105C?

tom zhang said:

Does this also for 105C?

James, 

Can you please provide your inputs for this case ?

Then, we can hopefully close the thread.

Regards

Ashwani

The TCR settings would apply to both 95C and 105C, but they will behave differently as mentioned earlier in the thread.

Regards,

James

Hi Ashwani:

You can get the ddr_configurations I have uploaded.
I only changed the 3 settigs:

  LPASR mode:  Manual mode, Extended temp

  TCR mode: Enabled

  TCR range: Extended

Hi JJD:

   ok, thank you. I will test this.

thanks, please let me know the results

james

Dear Tom.

may I ask you to provide test result? 

And what is the schedule to deploy ISSI DDR in your system?

thanks a lot!

yong

Dear Tom.

any update?

thanks a lot!

yong

Hi Yong：

     For 95C and 105C, we use the config

          LPASR mode:  Manual mode, Extended temp

          TCR mode: Enabled

          TCR range: Extended

    the system loading is higher than 85C configs, but not 100%.This does not meet our current requirements

   At first we tested for 95C and 105C, we set TCR mode = disabled, the system loading is 100%.

Dear JJD,

would you please help check the test result from seyond team? any more suggestion?

tom zhang  May I ask if there is feedback on the test result from ISSI? Actually, AM620-Q1 works as host on DDR I/F, it seems the loading reduced when TCR enabled w/o magnificent optimization.

thanks a lot!

yong

Hi Yong:

   There is no test result from ISSI.

Hi Tom,

tom zhang said:

the system loading is higher than 85C configs, but not 100%.

so the system loading was reduced with TCR mode enabled, but not to your expectations?  I don't think there is much more we can do, as we have to meet JEDEC spec at temps above 85C.  This is a requirement of the memory. 

Regards,

James

Hi JJD：

      Sorry, the system loading was increased with TCR mode enabled.

      For example, without TCR mode enable, the system loading maybe 80%

      With TCR  mode enable,  the system loading maybe 85%

Ok, that doesn't seem to make sense to me.  Were they both using the same refresh rate? 

Regards,

James

Hi JJD:

  80%s system loading: using 85C ddr configuration  with TCR mode disable.

  85%s system loading: using 95C or 105 ddr configuration  with TCR mode enable.

tom zhang said:

80%s system loading: using 85C ddr configuration  with TCR mode disable.

  85%s system loading: using 95C or 105 ddr configuration  with TCR mode enable.

were you operating <85C when measuring system load in these cases?  

I think we want to compare

1) what is system load operating at <85C, using 85C DDR configuration with TCR mode disabled ( i think you said previously this is 80%)

2) what is system load operating at <85C, using 95C DDR configuration with TCR mode enabled, TCR range extended

3) what is system load operating 85-95C, using 95C DDR configuration with TCR mode enabled, TCR range extended

I think #2 should be less than #3, based on the table mentioned above.  And that is the only improvement we could make to just running 3.9us refresh rate exclusively.

Regards,

James

Dear Tom.

would you please help answer the questions from JJD? or provide the status?

thanks a lot!

yong

Dear Tom.

per discussion in Wchat, it seems you have accepted the performance after retest, right?

would you please share us the final setting to let us align on the status?

and also, we would like to close this ticket in this week if no more support required from TI. Please let us know your comment.

thanks a lot!

yong

Hi Yong:

We tested 4 different configs at room temperature.

For 95C and 105C, the cpu usage is higher than 85C.

We want to check this:

As enable TCR mode  at room temperature, the REFI of 95C and 105C should auto be setted as 7800, which is same as tREFI of 85C.

Is this right? why the cpu usage is higher than 85C?

Hi Tom, i think the results you show are correct.  I would consider cpu usage of 88 vs 89.2 to be practically equivalent.  I'm not sure how much granularity you have in this measurement.

Shown below, you can see which mode each scenario is running.  Scenario 3 takes advantage of TCR and reduces the internal refresh period relative to the external refresh period.  However, when running at 105C (Scenario 4), cpu usage trends higher because there is no advantage using TCR mode (ie, external/internal refresh period are the same) 

Regards,

James

Hi JJD：

 But the temperature is not 105C, at room temperature maybe is about 23C.

 DDR vendor tell us that the tREFI is setted by Soc to control DDR to refrash.

 We think if TCR mode works, all at 23C, the cpu usage of different configurations should be same. 

Hi Tom, yes, but when configuring for 105C, the refresh period is fixed at 1.95us.  We do not have dynamic refresh rate support for DDR4.  So the external refresh period will stay at 1.95us, and thus will not be different than the internal refresh period at any temperature.  My understanding is that TCR mode is only advantageous with a 3.9us refresh period.  

Regards,

James

Hi JJD:

    So TCR mode only supports a maximum temperature of up to 95°C on am62X, is that right?

    For 105C or higher,  the refresh period will be a fixed value even if we set TCR enable, right?

TCR mode is a feature of the memory, not AM62x.  The memory only changes the internal refresh mode when using a external refresh period of 3.9us (as shown in the table below).  When you set a refresh period of 1.95ns or 0.975ns (which is necessary for 105C and 125C respectively), TCR mode is not advantageous.

Regards,

James

Dear Tom.

please let us know if you still need help from TI. we would like to close this ticket in this week as no more questions.

thanks a lot!

yong

Hi Yong:

   Thank you for your help.You can close the ticket.

   We will test the configuration: 95C ,tREFI=3.9us with TCR mode