Patch for u-boot mainline master (http://git.denx.de/u-boot.git) to prevent BBB’s to get stuck in a u-boot prompt because of spurious characters being received on the serial console (see http://www.mikini.dk/index.php/category/beaglebone-black/boot-issue).

diff –git a/include/configs/ti_am335x_common.h b/include/configs/ti_am335x_common.h
index 5ed86d9..c58f467 100644
— a/include/configs/ti_am335x_common.h
+++ b/include/configs/ti_am335x_common.h
@@ -12,6 +12,12 @@
#ifndef __CONFIG_TI_AM335X_COMMON_H__
#define __CONFIG_TI_AM335X_COMMON_H__

+#define CONFIG_AUTOBOOT_KEYED
+#define CONFIG_AUTOBOOT_STOP_STR “stop”
+#define CONFIG_AUTOBOOT_PROMPT “autoboot in %d seconds (type ‘%s’ to abort)\n”,bootdelay,CONFIG_AUTOBOOT_STOP_STR
+#define CONFIG_BOOT_RETRY_TIME 30
+#define CONFIG_RESET_TO_RETRY
+
#define CONFIG_AM33XX
#define CONFIG_ARCH_CPU_INIT
#define CONFIG_SYS_CACHELINE_SIZE       64
@@ -102,4 +108,7 @@
/* Now bring in the rest of the common code. */
#include <configs/ti_armv7_common.h>

+#undef  CONFIG_BOOTDELAY
+#define CONFIG_BOOTDELAY               5
+
#endif /* __CONFIG_TI_AM335X_COMMON_H__ */

Patch and compiled binaries at http://www.mikini.dk/wp-content/uploads/2015/01/u-boot_mainline_BBB-autoboot-patch_201501151.zip.

Install the new u-boot by copying the files “MLO” and “u-boot.img” to the root directory of your boot device (first FAT-partition on your SD-card or onboard MMC). Using the stock Debian image (http://beagleboard.org/latest-images) this can be done via USB by powering the board from your computers USB-interface, waiting for the BBB to boot and register its drive as an usb mass-storage in your OS. Now use your favorite file management application to copy the files from the above zip-file replacing the existing files.

Disclaimer: this is mostly an experiment, there is a lot of u-boot trees and patches floating around for the BBB (like https://github.com/beagleboard/u-boot), so probably mainline hasn’t got the most recent stuff for AM335x/BBB yet.