source: umon/ports/beagleboneblack/README @ c900821

Getting Started with uMon for the Beaglebone Black

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Booting:
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SD Card:
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The Beaglebone Black can boot uMon from an SD card using two different
boot modes.  The first boot mode is to boot using "raw" mode.  The
second boot mode is to boot from a FAT primary partition marked as
bootable.  The details and the steps required to set up the SD card
for each of the boot modes are elaborated in the following two sections
on SD card booting.  For more information on "raw" mode and FAT mode,
please refer to the AM335s TRM Sections 26.1.7.5.5 "MMC/SD Read Sector
Procedure in Raw Mode" and 26.1.7.5.6 "MMC/SD Read Sector Procedure
in FAT Mode" respectively.

In order to boot uMon from an SD card using FAT mode, a GP Header must
be prepended to the uMon image.  In the case of booting uMon using
"raw" mode, both a Configuration Header TOC Structure followed by a
GP Header must be prepended to the uMon image.

The GP Header is 8 bytes long where the first 4 bytes specify the size
of the uMon image that will be transferred while the last 4 bytes
specify both the destination address where the uMon image will be
transferred to and the entry point.

For information on the layout of the Configuration Header TOC Structure
required for "raw" mode booting, please refer to the AM335x TRM
Section 26.1.7.5.5.1 "Configuration Header".

One thing worth mentioning is that the Beaglebone Black is connected to
the SD card using MMC0 and as a result the size of the SD card must not
be greater than 4GB.  This is indicated in the AM335x TRM Section
26.1.7.5.2 "System Interconnection".

In order to configure the Beaglebone Black to boot from an SD card,
a uSD must be inserted and the boot switch held down while the board
is powered up.  Once the board is powered on, the boot switch can
be released.  If the attempt to boot from the uSD fails, the
Beaglebone Black will fall back and attempt to boot using UART.
As a result, this will provide a way to determine whether the boot
from SD has succeeded or not.

Before starting, it is recommended that the device that will be
manipulated is verified to be the right device.  An approach to
determine the right device name assigned to the SD card is by
observing the output of

        cat /proc/partitions

before and after inserting the SD card.


RAW MODE:

In order to boot from an SD card using "raw" mode, the uMon image
must be prepended with a Configuration Header TOC Structure and a
GP Header.  The GP Header is placed right after the Configuration
Header TOC Structure.

When uMon is built, a uMon image containing the necessary headers
is already created and is located under ./build_BEAGLEBONEBLACK.

The next step is to setup the SD card.  Fortunately, the script
./sd_setup.sh can be used to automate the process of setting up
an SD card for "raw" mode booting.  To do so, invoke the script as

        ./sd_setup.sh RAW <device>

<device> shown above and for the remainder of this document will
refer to the SD card.

The following information specify how to manually set up the SD
card.

With the proper headers prepended, the image is ready to be booted.
In order for the Beaglebone Black/AM335x to boot the image, the
image must be placed at one of the offsets
0x00000/0x20000/0x40000/0x60000.

As an example, to place the uMon image at the first offset

        # Get the size of the uMon image to transfer into the SD card
        export UMON_IMG_SIZE=`wc --bytes <uMon image> | cut -f 1 -d ' '`

        # Transfer the uMon image at offset 0x00000
        dd if=<uMon image> bs=1 count=$UMON_IMG_SIZE of=/dev/<device>

where <uMon image> is the path to the uMon image prepended with a
Configuration Header TOC Structure and a GP Header.


FAT MODE:

In FAT Mode, an "MLO" file is searched for in the root directory of
a primary partition formatted as FAT12/FAT16 or FAT32 and marked
bootable.  This "MLO" file must contain a GP Header followed by the
uMon image.  When uMon is built, an "MLO" file is already created and
is located in ./build_BEAGLEBONEBLACK.

For convenience, preparing the SD card for FAT Mode booting has
been automated through the use of the same aforementioned script,
./sd_setup.sh.

Invoking the script in order to create an SD card for FAT mode booting
is as follows:

        ./sd_setup.sh FAT <device>

The script simply sets up a primary partition on the SD card, marks
it as bootable, formats it as FAT16 and then transfers the MLO file
under ./build_BEAGLEBONEBLACK to the root directory of the primary
partition on the SD card.

The following elaborates the sequence of steps on how exactly an SD
card is prepared for FAT Mode booting for the Beaglebone Black
to boot from.

Assuming that the SD card has not been formatted yet...

Just to be safe, clear out the partition table at the base of the SD
card to start fresh.

        dd if=/dev/zero of=<device> bs=1M count=1

The next step is to create a primary partition with the filesystem
type set to FAT16.  This primary partition will be placed as an entry
in an MBR located in the first sector of the SD card.  Fortunately,
these intial steps are taken care of by the fdisk utility.

To allocate a partition that will be formatted as FAT16 and to create
an entry for the partition in the MBR,

        fdisk <device>

Suppose the SD card is registered under /dev as "sdc", this would be

        fdisk /dev/sdc

fdisk will then present a command-line dialog.

From here, a new partition must be created using 'n'.  This partition
must have a type of 0x06 for FAT16 which is set with 't' and with the
size allocated to the partition to be at least 3MB.  This size is the
minimum size required and is more than enough to hold a uMon image and
to allow for future expansion.  It is recommended that not all of the
sectors of the SD card are allocated to the FAT16 primary partition
in order to provide room for the possibility of storing user data or
perhaps a kernel.

Once that is done, the next step is to mark the primary partition as
bootable.  This is done using the 'a' option.

With all that in place, the partition can be verified before writing
it to the SD card with 'p'.  Once the partition has been verified,
it can be written to the SD card using 'w'.

After using fdisk to set up the partition, the new partition can be
viewed under /dev.  So for example, if the base of the SD card is given
as /dev/sdc, then the newly created FAT16 partition will be given as
/dev/sdc1.

The next step is to format this partition as FAT16:

        mkfs.fat -f 2 -F 16 -M 0xF8 -s 1 -S 512 <device>

with <device> set to the primary partition of the SD card.

The final step is to place the "MLO" file in the root directory
of the FAT16 primary partition.

        cd ~
        mkdir mnt
        mount <device> mnt
        cp <path_to_umon>/ports/beagleboneblack/build_BEAGLEBONEBLACK/MLO mnt
        umount mnt
        rmdir mnt

In the previous set of commands, <device> is set to the primary
partition of the SD card that was recently formatted as FAT16.

The SD card is now ready.


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eMMC:
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Booting uMon from the onboard eMMC requires a multiple-step procedure
that will be simplified in the future as the uMon port progresses.

To transfer a uMon image into the onboard eMMC requires an SD card where
uMon is configured to boot in RAW mode from a known offset.

With uMon configured to boot in RAW mode from a known offset in the
SD card, the next step is to determine the size of the uMon image in
512-byte blocks.

With all of this in place, the sequence of uMon commands required to
transfer the uMon image are as follows:

    sd init
    mmc init
    sd read <destination in RAM> <SD sector address> <# of 512-byte blocks>
    mmc write <source in RAM> <eMMC sector address> <# of 512-byte blocks>

With these steps, the uMon image is first transferred into DDR3 RAM
and then written to the eMMC.  The reason for this appraoch is that
there is currently no supported mechanism to write the eMMC directly
from an SD card.

The user must take care to transfer the uMon image in a location in
RAM not currently owned by the uMon image currently in execution.

As for the final destination in the eMMC, the uMon image must be stored
in a locatation where the internal ROM-bootloader will be able to find
and boot this image.


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UART:
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Unlike booting from SD, booting via UART does not require any GP
Header, Configuration Header TOC Structure, or both to be prepended to
the uMon image.  The uMon image that will be booted using UART is
boot.bin which is located in ./build_BEAGLEBONEBLACK.

In order to boot from UART, a 3.3V USB-to-Serial cable is required,
e.g. the FTDI USB TTL Serial cable is a possible option.

The last requirement is to have a terminal emulator
(e.g. minicom/picocom/etc.) set up to perform XMODEM transfers using
1K packets and 16-bit CRC.

To initiate the UART booting procedure on the Beaglebone Black, ensure
that there is no uSD card inserted and then hold the boot switch down
while powering up the board.  Once the board is powered on, the boot
switch can be released.

If a terminal emulator is set up already and connected to the serial
port of the Beaglebone Black, the character 'C' will be outputted
continuously.  This indicates that the UART booting procedure has
initiated and is waiting for an image to be transferred via UART.

From here, the uMon image can now be transferred using the terminal
emulator.

For more information on the UART boot procedure, please refer to the
AM335x TRM Section 26.1.8.5 "UART Boot Procedure".
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