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{{ImportantMessage|text=SBC Lynx is extremely flexible in terms of hardware configurations. This document describes main options related to booting. In case you need a configuration that is not listed here, please contact [mailto:sales@dave.eu|Sales department].}}
==Introduction==
Interested reader may find an exhaustive discussion of iMX6UL boot options in the ''Applications Processor Reference Manual''<ref name="IMX6ULRM">NXP, IMX6ULRM, ''i.MX 6UltraLite Applications Processor Reference Manual''</ref>.
==Available options==
By default, eFUSE bits are not supported as bootstrap option [1]. Thus , two actual modes can be selected by S12.1 and S12.2 switches, as listed in the following table.{|class="wikitable" style="text-align: center;"
|-
!BOOT_MODE[1:0]
| 10||Internal boot||on||off||Default
|-
| 11||reserved|| on || on ||'''Reserved'''
|}
[1] Nevertheless, SBC Lynx can support this option. This is a clear example of a feature that can be implemented on request. For more information please contact [mailto:sales@dave.eu|Sales department].
===Internal boot===
When ''Internal boot'' mode is selected, ''GPIO override'' technique is used to configure bootstrap flags, also known as <code>BOOT_CFG</code> bits. This means that 24 processor's signals - specifically LCD1_DATA[23:00] - are latched by iMX6UL processor upon reset to get bootstrap flags. As such, these signals need to be pulled up or down to select the proper configuration.
The following table summarizes these configurations. Pull-up/down resistors are 10kOhm.
{|class="wikitable" style="text-align: center;"|-!<code>BOOT_CFG</code> bits!Pull|-| LCD_DATA23 (BOOT_CFG4_7) || pull-down |-| LCD_DATA22 (BOOT_CFG4_6) || pull-down |-| LCD_DATA21 (BOOT_CFG4_5) || pull-down |-| LCD_DATA20 (BOOT_CFG4_4) || pull-down |-| LCD_DATA19 (BOOT_CFG4_3) || pull-up |-| LCD_DATA18 (BOOT_CFG4_2) || pull-down |-| LCD_DATA17 (BOOT_CFG4_1) || pull-down |-| LCD_DATA16 (BOOT_CFG4_0) || pull-down |-| LCD_DATA15 (BOOT_CFG2_7) || pull-up |-| LCD_DATA14 (BOOT_CFG2_6) || pull-up |-| LCD_DATA13 (BOOT_CFG2_5) || pull-up |-| LCD_DATA12 (BOOT_CFG2_4) || pull-up |-| LCD_DATA11 (BOOT_CFG2_3) || pull-up |-| LCD_DATA10 (BOOT_CFG2_2) || pull-down |-| LCD_DATA09 (BOOT_CFG2_1) || pull-up |-| LCD_DATA08 (BOOT_CFG2_0) || pull-up |-| LCD_DATA07 (BOOT_CFG1_7) || pull-down |-| LCD_DATA06 (BOOT_CFG1_6) || pull-down |-| LCD_DATA05 (BOOT_CFG1_5) || pull-up |-| LCD_DATA04 (BOOT_CFG1_4) || pull-up |-| LCD_DATA03 (BOOT_CFG1_3) || pull-up
|-
|-
| XUBx0xxx<br>XUBx2xxx|| pull-down || pull-down || pull-down || pull-down || pull-up || pull-down || pull-down || pull-down || pull-up LCD_DATA01 (BOOT_CFG1_1) || pull-up || pull-up || pull-up || pull-up || pull-down || pull-up || pull-up || pull-down || pull-down || pull-up || pull-up || pull-up || pull-up || pull-up || pull-up ||
|-
| XUBx1xxx<br>XUBx2xxx|| TBD || TBD || TBD || TBD || TBD || TBD || TBD || TBD || TBD || TBD || TBD || TBD || TBD || TBD || TBD || TBD || TBD || TBD || TBD || TBD || TBD || || TBD || TBD || TBD LCD_DATA00 (BOOT_CFG1_0) ||pull-up
|}
The following chart depicts the general boot flow of SBC Lynx models equipped with NOR flash. It is worth noticing that, if the flow falls in the ''serial downloader'' branch, the BootROM performs an attempt to boot from microSD card too, as the ''Manufacture mode'' is enabled. This mode can be a convenient solution for different needs (for example, to recover a board where U-Boot was erased accidentally from NOR flash). For more information, please refer to [[How_to_create_a_bootable_microSD_card_(XUELK)|this page]] and [[Standalone_boot_(XUELK)#U-Boot|this page]].
[[File:SBCLynx-boot-XUBx0000.png|thumb|center|600px|Boot flow of ordering codes XUBx0000]]
===Serial downloader===
Generally speaking, serial downloader allows downloading a program image to the target over USB or UART connections.
The following flowchart details the sequence of operations that are performed by BootROM in Serial Download mode (source ''Applications Processor Reference Manual''<ref name="IMX6ULRM" />.
[[File:IMX6UL-serial-downloader-flow-chart.jpg|thumb|center|600px|Serial download boot flow]]
In case <span id="manuf_mode">''Manufacture mode''</span> is enabled, before probing UART/USB interface, BootROM tries to boot from SDHC1 interface if any device is connected to it.
The following sections provide additional notes related to the use of Serial Downloader on SBC Lynx in order to warn the user about possible conflicts that may occur depending on what is connected to USBOTG1 port, UART1 and UART2 interfaces.
Some additional information related to the interfaces used by ''serial downloader'':
*UART1: this UART is routed to connector J42 that is typically used for the console.
*UART2: this UART is routed to connector J46 that is dedicated to optional [[Wireless_Module_(DWM)|DWM WiFi/Bluetooth module]]. Even if DWM is populated, no electrical conflicts occur.
*USBOTG1: this interface is connected to J55. The use of this port is user-defined.
==References==
{{reflist}}
