Date: Mon, 26 Jan 2015 08:35:51 +0200 From: matti kaasinen matti.kaasinen@gmail.com To: "u-boot@lists.denx.de" u-boot@lists.denx.de Subject: [U-Boot] usb flash boot on am335x machines Message-ID: CADnUhn33Oo-vguOFKoq0-7R0dztAohbOoCrX2qZSA9LT1SvE0w@mail.gmail.com Content-Type: text/plain; charset="utf-8"
Hi!
I have tried to find solution to get am335x based Silica/Pengwyn board booting from usb flash. U-boot on that board is based on u-boot 2013.10. I flashed it with similar configuration as mmc flash, but I did not find combination of configuration variables to get proper spl code generated. I studied codes and it seemed like am33x devices were left out from usb spl generation parts. Is there some kind of fundamental reason to prevent am335x devices not to boot from usb flash. If not, would anyone know the configuration combination for this set-up.
If you read the TRM carefully (26.1.8.6 USB Boot Procedure), you'll find out that the 335x doesn't support usb flash drive boot at the hardware level. The USB boot option that is available creates a RNDIS ip connection with a computer and then it does a network boot. I'll agree that this wasn't what I was expecting when I saw USB boot.
The only way to support a USB flash boot would be if the SPL was loaded some other means (NOR, NAND, MMC, etc) and it mounted the flash drive and booted from it.
In fact, I found more than three years old patch that seems to make usb boot set-up for am335x devices: https://gitorious.org/rowboat/u-boot/commit/aaa9d5c083252218fd89afa68161f96b... However, it seems that these changed have somehow not been included in the mainline codes. Is there specific reason for this?
Sorry if this doesn't correctly link to original post. I'm unsure how I'm supposed to reply to an email in a mailing list digest.