clearfog: Implement USB booting
Here's how to load this from a possible bricked device:
1) Set the boot switches to 01001 (yes, it's different from what the doc
says)
2) Load the bootloader via UART, e.g.:
`./tools/kwboot -b ./u-boot-spl.kwb -t -p /dev/ttyUSB0`
3) Interrupt U-Boot's autoboot to get a prompt
4) Plug a USB flash with images/usb-flash.img loaded
5) One on the U-Boot prompt, execute:
`usb start; fatload usb 0:1 00800000 usb-boot.scr; source 00800000`
6) Get a nice emergency shell
Change-Id: Icef4badc9105bbed78ad949c060c0a46e9ff7f76
diff --git a/board/czechlight/clearfog/usb-boot.scr.txt b/board/czechlight/clearfog/usb-boot.scr.txt
new file mode 100644
index 0000000..0227a74
--- /dev/null
+++ b/board/czechlight/clearfog/usb-boot.scr.txt
@@ -0,0 +1,5 @@
+setenv bootargs systemd.unit=emergency.target
+fatload usb 0:1 ${kernel_addr_r} zImage
+fatload usb 0:1 ${fdt_addr_r} czechlight-clearfog.dtb
+fatload usb 0:1 ${ramdisk_addr_r} rootfs.cpio.uboot
+bootz ${kernel_addr_r} ${ramdisk_addr_r} ${fdt_addr_r}