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BCOS Boot Script Variables

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Contents:

Chapter 1: Overview

During boot the operating system's behaviour is influenced by variables in a boot script. This document describes each possible variable and how it influences the operating system's behaviour.

Chapter 2: Boot Script Variable Reference

2.1. DIDdisableHead0, DIDdisableHead1, ..., DIDdisableHead999 (boolean)

If this boolean is present and set to "yes" (or "true"), during boot the operating system will not use display identification data for the display corresponding to the specified head number, most likely resulting in a "safe video mode timing" (e.g. 640*480) being used for that display.

These variables should only be used to work around problems (e.g. where displays provide incorrect information and the operating system doesn't or can't work around the problem). These variables take precedence over other variables that effect the use of display identification data for the corresponding head.

2.2. DIDdisableHeadAll (boolean)

If this boolean is present and set to "yes" (or "true"), during boot the operating system will not use display identification data for all displays (for all head numbers), most likely resulting in a "safe video mode timing" (e.g. 640*480) being used for all displays.

This variable should only be used to work around problems (e.g. where the display provides incorrect information and the operating system doesn't or can't work around the problem). This variable takes precedence over other variables that effect the use of display identification data for all heads.

2.3. DIDforceHead0, DIDforceHead1, ..., DIDforceHead999 (string)

If any of these variables are set and contain a string with a valid format, the vendorID and productID for the display corresponding to the specified head number is forced to the vendorID and productID contained in the variable. To be considered valid, the string must be formatted as described by Subsection 2.3.1. Vendor ID and Product ID String Format.

These variables should only be used to work around problems (for displays that provide incorrect vendorID and productID). These variables have no effect if the use of display identification data is disabled for the head or disabled for all heads, and takes precedence over other variables that effect the use of display identification data for this head or all heads.

2.3.1. Vendor ID and Product ID String Format

A valid display identification data vendor ID and product ID string consists of 4 upper-case letters or '_', followed by followed by '_', followed by 4 hexadecimal digits ('0', '1', ..., '9', 'A', ..., 'F'). Examples:

2.4. DIDforceHeadAll (string)

If this variables is set and contain a string with a valid format, the vendorID and productID for all displays is forced to the vendorID and productID contained in the variable. To be considered valid, the string must be formatted as described by Subsection 2.3.1. Vendor ID and Product ID String Format.

This variable should only be used to work around problems (e.g. where the display provides incorrect information and the operating system doesn't or can't work around the problem). This variable has no effect if the use of display identification data is disabled for the head or disabled for all heads, or if the head has already been forced to use a specific vendorID and productID; and takes precedence over other variables that effect the use of display identification data for this head or all heads.

2.5. DIDdefaultHead0, DIDdefaultHead1, ..., DIDdefaultHead999 (string)

If any of these variables are set and contain a string with a valid format, the vendorID and productID contained in the variable is used if no information can be obtained. To be considered valid, the string must be formatted as described by Subsection 2.3.1. Vendor ID and Product ID String Format.

These variables should only be used to work around problems (e.g. if the boot loader was unable to obtain any information about the display). These variables have no effect if the use of display identification data is disabled for the head or disabled for all heads, or if display identification data is forced for the head or forced for all heads, or if boot code can obtain information about the device.

2.6. DIDdefaultHeadAll (string)

If this variable is set and contains a string with a valid format, the vendorID and productID contained in the variable is used if no information can be obtained and no other default has been set. To be considered valid, the string must be formatted as described by Subsection 2.3.1. Vendor ID and Product ID String Format.

This variable should only be used to work around problems (e.g. if the boot loader was unable to obtain any information about the display). This variable has no effect if the use of display identification data is disabled for the head or disabled for all heads, or if display identification data is forced for the head or forced for all heads, or if boot code can obtain information about the device, or if a specific head already has a default.

Generated at 17:52:20 on the 28th of June, 2017 (UTC)