[FAQ] J721S2XSOMXEVM: How to change DDR frequency for J721E EVM, J721S2 EVM, and J784S4 EVM?

Prerequisites:

1. Please reference the J7 DDRSS Register Configuration Tool Appnote for the spreadsheet used in this FAQ: https://www.ti.com/lit/an/spracu8b/spracu8b.pdf. The spreadsheet runs best through Excel on a Windows PC.
2. PSDK Linux for the EVM. For example, if using J721S2/TDA4VE, then download from here: https://www.ti.com/tool/download/PROCESSOR-SDK-LINUX-J721S2
   

Below steps will be using J721S2/TDA4VE/TDA4VL as an example, and using the 8.6 version of the SDK.

Steps:

1) Load default config from title page

2) Set the frequency (clock which is half of the data rate, so below is configured for 4266)

3) On the timing tab, update below latency parameters using tables from DDR datasheet (copied below)

As a sidenote for where these parameter numbers come from: The DDR part used for the J721S2 EVM can be obtained from the BOM excel sheet included with the Design Files of the EVM: https://www.ti.com/tool/J721S2XSOMXEVM. At least for all Jacinto EVM, BOM is always included with design files of the EVM. For J721S2, MT53E2G32D4DT-046 AAT:A is the DDR part, and Googling eventually leads you to the datasheet of this DDR part: https://media-www.micron.com/-/media/client/global/documents/products/data-sheet/dram/mobile-dram/low-power-dram/lpddr4/200b_z32m_sdp_ddp_qdp_auto_lpddr4_lpddr4x.pdf?rev=c85c105d5d26455f8d7a40d021703364.

4) Generate file

5) Copy and paste the generated DTSI file into U-Boot. The "ti-processor-sdk-linux-j7-evm-08_06_01_02/board-support/u-boot-2021.01+gitAUTOINC+62a9e51344-g62a9e51344/arch/arm/dts/k3-j721s2-ddr-evm-lp4-4266.dtsi" is the file used by U-Boot, so replace this.

6) Rebuild U-Boot and reinstall with "make u-boot" and "make u-boot_install". Details here: https://software-dl.ti.com/jacinto7/esd/processor-sdk-linux-j721s2/09_00_01_02/exports/docs/linux/Overview_Top_Level_Makefile.html#usage-examples

7) Verify if DDR frequency has been changed with k3conf tool. Details here for J721E: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1169373/faq-tda4vm-how-to-read-the-ddr-frequency-from-linux. J721S2/J784S4 will have different device ID for DDR, but similar name, so output of k3conf can be piped into grep to search for DDR related clock info.

Regards,

Takuma