iMX6UL JTAG RAM Performance

[chris16]

Can anyone help me figure out why I'm seeing slower performance on the iMX6UL-EVK when a u-boot image is loaded via JTAG vs when it is loaded from the sdcard? I suspect it has to do with the DDR configuration. In the sdcard instance, u-boot's SPL is initializing the system. In the JTAG instance, I'm loading u-boot and an image.fit directly into RAM and executing after setting registers. Just hand-timing the boot time between the two I see u-boot take ~8 seconds to boot the image.fit from the sdcard, but it takes ~36 seconds to boot the same image.fit when its loaded into RAM via JTAG. I'll attach the files I'm using to test this but you can also find the files in a public repo here: buildroot-imx6ulevk-test/board/freescale/imx6ulevk at master · cryptotronix/buildroot-imx6ulevk-test... 

The u-boot is mainline, v2018.05, with a slightly modified mx6ul_14x14_evk_defconfig to enable the FIT image support.

Note: in order to test the JTAG version you'll need a segger j-link, with the imx6ulevk having had the resistor changes to enable JTAG. You can run the flash.sh script to load the imx6, to see the slower boot time you'll need to break u-boot's autoboot and type the command: "bootm 0x90000000", which is where the image.fit has been loaded into RAM by the jlinkscript

[chris16]

For anyone else that stumbles upon this, I made edits to the jlinkscript after finding the imximage.cfg file from a freescale u-boot-imx repo. I'll attach the files here. The performance is now similar to booting from sdcard!

[b36401]

Actually in case of JTAG the performance is limited with JTAG interface not memory.
Please note that JTAG is not very fast.
JTAG frequency is allowed from 1KHZ to 22MHz for i.MX6UL however typicalli it is about 1MHz.

[chris16 · Accepted solution]

Thanks for the response! I'm aware of the slower speed of JTAG itself, but the performance issues I'm seeing are when u-boot is running. My hunch was that the jlinkscript I'm using to set DDR registers is missing some settings that are required in order to fully configure the imx6. I think I've actually solved the problem now after finding an imximage.cfg file for the EVK and comparing the jlinkscript to the register settings in there. After reconciling the two files the JTAG u-boot performance is now just as fast as sdcard performance!