Difference between revisions of "Boot process and bootstrap configuration (AXEL ULite)"

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(Introduction)
(Overview of NXP iMX6UL bootstrap process)
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!BOOT_MODE[1:0]
 
!BOOT_MODE[1:0]
 
!Boot type
 
!Boot type
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|-
 
| 00||Boot from eFUSEs
 
| 00||Boot from eFUSEs
 +
|-
 
| 01||Serial downloader
 
| 01||Serial downloader
 +
|-
 
| 10||Internal boot
 
| 10||Internal boot
 +
|-
 
| 11||reserved
 
| 11||reserved
 
|}
 
|}
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===Boot from eFUSEs===
 
===Boot from eFUSEs===
 
The term eFUSEs refer to an one-time-programmable (OTP) memory integrated in iMX6UL processor. This memory is organized in several 32-bit words. Three of these words - named BOOT_CFG - are used to store configuration bits that affect boot process, when ''Boot from eFUSEs'' mode is selected. In this case, Boot ROM reads BOOT_CFG words and acts consequently.
 
The term eFUSEs refer to an one-time-programmable (OTP) memory integrated in iMX6UL processor. This memory is organized in several 32-bit words. Three of these words - named BOOT_CFG - are used to store configuration bits that affect boot process, when ''Boot from eFUSEs'' mode is selected. In this case, Boot ROM reads BOOT_CFG words and acts consequently.
 +
 +
BOOT_CFG includes many configuration settings. Two of them are particularly important for the boot strategy:
 +
*BT_FUSE_SEL
 +
*SDMMC_MFG_DISABLE.
 +
The use of these settings will be more clear soon.
  
 
===Serial downloader===
 
===Serial downloader===
 +
Serial Downloader mode is used to download a Program Image - that is a file that can be executed by the processor - over one of the following connections:
 +
*USB OTG1
 +
*UART1
 +
*UART2
  
 
===Internal boot===
 
===Internal boot===
  
 
===Typical scenario===
 
===Typical scenario===
 
 
  
 
==Options for AXELULite users==
 
==Options for AXELULite users==

Revision as of 07:49, 8 June 2016

Introduction[edit | edit source]

NXP iMX6UL processor implements a very flexible boot process. This versatility comes at the price of a non trivial bootstrap configuration scheme. Typical system-on-module (SOM for short) adopter does not want/need to deal with such complexity. In other words he/she expects to manage few boot configuration issues because it is assumed they are handled by the SOM itself. Nevertheless, there are specific applications where the system integrator needs full control of all the bootstrap configuration options, even if the design is built upon a SOM.

These two needs - ease of use and configurability - clearly push in opposite directions. During the conception of the product AXELULite, specific attention has been addressed to find a viable trade off to satisfy such requirements. This effort has led to the options that are detailed in the section Options for AXELULite users. Before skipping to it, it is recommended to read this section that depicts an overview of the processor's boot process. For more details about it please refer to [1]

Overview of NXP iMX6UL bootstrap process[edit | edit source]

When it comes to boot process, three factors play a major role:

  • BOOT_MODE signals (BOOT_MODE1, BOOT_MODE0)
  • eFUSE bits
  • GPIO settings.

Generally speaking, three main boot modes are supported. These modes are selected by BOOT_MODE signals that are latched when processor comes out of reset.

BOOT_MODE[1:0] Boot type
00 Boot from eFUSEs
01 Serial downloader
10 Internal boot
11 reserved

It is worth remebering that, no matter what modes is selected, when processor reset is released, internal Boot ROM is executed. Its behavior depends on selected mode as described in the following sections.

Boot from eFUSEs[edit | edit source]

The term eFUSEs refer to an one-time-programmable (OTP) memory integrated in iMX6UL processor. This memory is organized in several 32-bit words. Three of these words - named BOOT_CFG - are used to store configuration bits that affect boot process, when Boot from eFUSEs mode is selected. In this case, Boot ROM reads BOOT_CFG words and acts consequently.

BOOT_CFG includes many configuration settings. Two of them are particularly important for the boot strategy:

  • BT_FUSE_SEL
  • SDMMC_MFG_DISABLE.

The use of these settings will be more clear soon.

Serial downloader[edit | edit source]

Serial Downloader mode is used to download a Program Image - that is a file that can be executed by the processor - over one of the following connections:

  • USB OTG1
  • UART1
  • UART2

Internal boot[edit | edit source]

Typical scenario[edit | edit source]

Options for AXELULite users[edit | edit source]

References[edit | edit source]

  1. NXP i.MX 6UltraLite Applications Processor Reference Manual