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AM4376: DRAM Chip Selects Question

Mark Pearson
Genius 12705 points
Part Number: AM4376


I have prototype Boards and I am having some troubles with DRAM.  I have two DDR3 chips like the AM437x EVM, but I noticed yesterday that it is using only one Chip select.  The schematic (in the PPTX file) shows that I used TWO chip selects.  One more each DDR3 chip.  I got the proto board to work by removing R906 and wiring the second DDR3 chip into CS0.  The quality of this isn’t great, but it works.  The jumper is short enough that the negative effects are not, as of yet, detrimental.

 

My questions are thus: Can I use two chip selects in 32bit mode?  If not, do I have to switch to 16 bit mode, and can I use two chips in 16 bit mode?  I would have to write to either or in that case I believe.

 DRAM Chip Select schematic clips.pptx

I found the following document: http://processors.wiki.ti.com/index.php/AM437x_DDR_Configuration_and_Programming_Guide#32-bit_or_16-bit_DDR.  It says that the 2 chip select feature is only used for LPDDR2 twin die configuration and set in EBANK in the EMIF4D_SDRAM_CONFIG register. 

 

I am now looking at section 5.13.8.2.1.3 of the data sheet.  I am not seeing setup that I intended to use.  What are your thoughts on all of this?

  • 0
    TI__Guru**** 161600 points
    I am looking into this. I will post my findings here.

    Best Regards,
    Yordan
  • 0
    TI__Genius 9655 points

    Mark Pearson said:

    My questions are thus: Can I use two chip selects in 32bit mode?  If not, do I have to switch to 16 bit mode, and can I use two chips in 16 bit mode?  I would have to write to either or in that case I believe.

    No. For x32 configuration, you need to route the entire x32 bus references a single chip select (DDR_CSn0 to be precise) like in the EVM. You can also refer to the Data sheet Table 5-50 which summarizes the configurations and Figure 5-49 thru Figure 5-53 which highlight the schematic connectivity for these configurations. I guess you might be able to make it work with x16 configuration with your current schematic, but you can use only 1 chip select. Essentially, your higher bytes and the 2nd DRAM will be useless.

    Mark Pearson said:

     

    I found the following document: http://processors.wiki.ti.com/index.php/AM437x_DDR_Configuration_and_Programming_Guide#32-bit_or_16-bit_DDR.  It says that the 2 chip select feature is only used for LPDDR2 twin die configuration and set in EBANK in the EMIF4D_SDRAM_CONFIG register. 

     

    I am now looking at section 5.13.8.2.1.3 of the data sheet.  I am not seeing setup that I intended to use.  What are your thoughts on all of this?

    We don't support dual rank systems with 2 chip selects on DDR3. Even if we did, the configuration you have is not correct. I'd suggest you to review the data sheet and ensure compliance to those. In your specific case, you need to make layout fixes to correct the chip select connection