Booting options (SBC Lynx)

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SBC Lynx-top.png Applies to SBC Lynx


200px-Emblem-important.svg.png 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 Sales department. 200px-Emblem-important.svg.png

Introduction

SBC Lynx is built upon NXP iMX6UL processor. This component supports several booting options that are summarized here. Reading of that section is recommended for understanding this document.

Interested reader may find an exhaustive discussion of iMX6UL boot options in the Applications Processor Reference Manual[1].

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.

BOOT_MODE[1:0] Boot type S12.2 (BOOT_MODE1) S12.1 (BOOT_MODE0) Notes
00 Boot from eFUSEs off off Supported on request only
01 Serial downloader off on
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 Sales department.

Internal boot

When Internal boot mode is selected, GPIO override technique is used to configure bootstrap flags, also known as BOOT_CFG 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.

BOOT_CFG 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
LCD_DATA02 (BOOT_CFG1_2) pull-up
LCD_DATA01 (BOOT_CFG1_1) pull-up
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 this page and this page.


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[1].


Serial download boot flow


In case Manufacture mode 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 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

  1. 1.0 1.1 NXP, IMX6ULRM, i.MX 6UltraLite Applications Processor Reference Manual