Uploading image to eMMC from JTAG

Hi everyone,

I want to upload custom U-Boot to eMMC. I have to do this via JTAG. How can I do that ? Is there any guilde to do this ?

maybe start by telling every one what board

Assuming it is a BeagleV-Fire, you can use the HSS’s USB mass storage mode. There is no utility I know of that would allow you to directly program the eMMC from JTAG.
Please refer to the Flashing eMMC section of this document (about half way down the page): Flashing gateware and Linux image — BeagleBoard Documentation