Add boot from other volumes in bootloader on targets with HAVE_MULTIVOLUME

Adds the ability to load firmware from other drives on MULTIVOLUME targets
Mihail Zenkov <mihail.zenkov@gmail.com> had posted a hard coded patch
to allow this on several Sansa players, I made it more universal

Redirect file rockbox_main.<name> should placed in root of
drive you would like to be main, if this file empty or there a single
slash '/' firmware will be loaded from /.rockbox in root of this drive
If instead a /<*DIRECTORY*> is supplied in rockbox_main.<name> then
firmware will be loaded from /<dir>/.rockbox/

NOTES*

The directory can have multiple levels however..
leading slash MUST be included
trailing slash can be omitted
(eg. /test/.rockbox would be simply '/test' in the redirect file)

Redirect file will not work on internal drive (whatever is default boot drive)

Volume with the highest index containing redirect file will be loaded
first.

Firmware file is checked for boot data region, if missing, firmware
image will not be loaded.

On failure or if no redirect file is found load will fallback to
internal drive

Currently only Sansa Fuze+, Sansa Clip+,
Sansa Clip Zip, Sansa Fuzev2, and Sansa Fuzev1 are implemented.

Players (with HAVE_MULTIVOLUME)
will need #define HAVE_BOOTDATA and #define BOOT_REDIR "rockbox_main.<name>"
added to their config file

boot_data is implemented in crt0.s file (See g#1552)
ARM and IMX233 have aleady been implemented

Once these conditions are met <HAVE_MULTIBOOT> will be defined by config.h

Partitions on the drives are able to have a redirect as
well.

Change-Id: Iada3263919f6bcad7d0d7d8279b4239aafa07ee9

1 files changed, 2 insertions, 0 deletions

diff --git a/firmware/export/config/sansaclipplus.h b/firmware/export/config/sansaclipplus.h
index cf2b1136a3..addf7d86c0 100644
--- a/firmware/export/config/sansaclipplus.h
+++ b/firmware/export/config/sansaclipplus.h
@@ -9,6 +9,8 @@
 #define FIRMWARE_OFFSET_FILE_CRC 0
 /* Define if boot data from bootloader has been enabled for the target */
 #define HAVE_BOOTDATA
+/* define boot redirect file name allows booting from external drives */
+#define BOOT_REDIR "rockbox_main.clip+"
 
 #define HAVE_MULTIDRIVE
 #define NUM_DRIVES 2