Embedian, Inc.
169
SMARC-iMX8MM Computer on Module User’s Manual
v. 1.2
4.7
Boot
Device
Selection
SMARC
hardware
specification
defines
three
pins
(
BOOT_SEL[0:2]
)
that
allow
the
Carrier
board
user
to
select
from
eight
possible
boot
devices.
SMARC
‐
iMX8MM
does
not
support
boot
up
from
SPI
flash.
If
TEST#
is
not
shunt
cross
to
GND,
the
first
stage
of
bootloader
on
SMARC
‐
iMX8MM
will
boot
up
from
on
‐
module
eMMC
first.
The
firmware
on
eMMC
will
read
the
boot
device
configuration
and
load
the
second
stage
bootloader
from
selected
boot
devices.
The
BOOT_SELx#
pins
are
weakly
pulled
up
on
the
Module
and
the
pin
states
decoded
by
module
logic.
The
Carrier
shall
either
leave
the
Module
pin
Not
Connected
(“Float”
in
the
table
below)
or
shall
pull
the
pin
to
GND,
per
the
table
below.
Carrier
Connection
BOOT_SEL2#
BOOT_SEL1#
BOOT_SEL0#
Boot
Source
0
GND
GND
GND
Carrier
SATA
1
GND
GND
Float
Carrier
SD
Card
2
GND
Float
GND
Carrier
eSPI
(CS0#)
3
GND
Float
Float
Carrier
SPI
4
Float
GND
GND
Module
Device
(USB)
5
Float
GND
Float
Remote
Boot
(GBE)
6
Float
Float
GND
Module
eMMC
Flash
7
Float
Float
Float
Module
SPI
If
TEST
#
pin
is
shunt
cross
to
GND,
the
first
stage
of
bootloader
on
SMARC
‐
iMX8MM
will
boot
up
from
off
‐
module
SD
card.
This
is
a
back
door
to
restore/upgrade
the
firmware
in
on
‐
module
eMMC
.
