49
OSD3358-SM-RED
– User Guide
Rev. 1.0 9/19/2017
Octavo Systems LLC
Copyright 2017
4.7
Boot configuration
The ROM code checks the SYSBOOT configuration pins to communicate information to the
processor such as, the OSC0 clock frequency, system boot source and boot sequence of the
board. The boot configuration functionality is multiplexed with the LCD interface pins of the
processor. The SYSBOOT pins are latched on the rising edge of PWRNONRSTN signal. After
boot, the pins can be used for LCD interfacing or other multiplexed functions. Table 26-7 of the
TRM (
http://www.ti.com/lit/ug/spruh73p/spruh73p.pdf
) describes the function of each boot
configuration pin. For the OSD3358-SM-RED Platform, the following boot configuration was
chosen.
Table 4: OSD3358-SM-RED sysboot pin functions
Pins
Value
Function
SYSBOOT[15:0]
0x401C
SYSBOOT[15:14]
01b
Input crystal frequency of OSC0
input is 24MHz
SYSBOOT[13:12]
00b
Reserved
SYSBOOT[11:6]
000000b
Don’t care for ROM code for the
OSD3358-SM-RED boot modes
SYSBOOT[5]
0b
CLKOUT1 disabled
SYSBOOT[4:0]
SYSBOOT[4:0] controls the boot sequence. The OSD3358-SM-RED has the ability to select
multiple boot sequences. The boot button S3 can be used to modify SYSBOOT[2] to change
the boot sequence of the processor. The boot button S3 must be pressed before power is
applied so that the correct value can be latched during power up. The boot sequence changes
are described in the following table allowing the processor to boot from the SD card slot even
when there is a valid image in the eMMC.
Table 5: OSD3358-SM-RED boot order
System change
Default
Boot button held
down
SYSBOOT[4:0]
11100b
11000b
Boot sequence priority
•
MMC1
•
MMC0
•
UART0
•
USB0
•
SPI0
•
MMC0
•
USB0
•
UART0
Figure 47 shows the boot configuration circuit in the OSD3358-SM-RED Board schematics.
