Peter Huewe: /* Remaining Issues */

2010-05-14T04:02:24Z

‎Remaining Issues

Chris at 10:13, 14 July 2007

2007-07-14T10:13:44Z

Wmat: Legacy Content Conversion

2006-12-15T18:51:49Z

Legacy Content Conversion

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VERSION 0.2

== Introduction ==

This specification is for Kernel Execute-In-Place (XIP). XIP refers to the capability for
a Linux kernel to be executed directly from a persistent, read-only memory or media type (usually
ROM or FLASH). When the kernel is executed in this fashion, the bootloader can avoid
loading the kernel from persistent storage, decompressing it, and saving it into system RAM.

== Rationale ==
The process of loading, decompressing, and writing a kernel to RAM is dependent on the size
of the kernel and the speed of the processor and the associated memory devices. An observed
time in practice is about 500 milliseconds. (For examples of observed time, please see the page
referred to in the References section below.) This time can be saved by avoiding these steps
and instead executing the kernel directly from its location in persistent storage.

== Specifications ==
#The Linux kernel SHALL support an option for executing the kernel directly from a persistent memory-mapped storage location.
#*The configuration option for kernel XIP MUST be called CONFIG_XIP_KERNEL
#When the option CONFIG_XIP_KERNEL is enabled, compilation of the kernel SHALL produce a kernel image that can be directly executed from ROM or FLASH.

== Notes (informational and non-normative) ==
#It is possible that FLASH memory being used for kernel XIP may not be available for other uses by the kernel which is being executed from it. Whether this is the case or not depends on the implementation details for the code which supports this specification. This specification does not currently require that the kernel be able to use the flash from which it executes for other uses (like filesystems.)

== References ==
See the page [[Kernel XIP]] for information about this feature, and for examples of time reductions that have been demonstrated with its use.

== Remaining Issues ==
*decide if we should address performance side effect of kernel XIP
*Figure out difference in usage or intent (if any) between use of CONFIG_XIP_ROM and CONFIG_XIP_KERNEL. Determine if the difference in feature set for execution from ROM vs. execution from FLASH (when flash is also used for filesystem operations) means that we should specify these separately.
*Decide if we should standardize use of CONFIG_XIP_PHYS_ADDR vs. CONFIG_XIP_KERNEL_TXTBASE

← Older revision		Revision as of 04:02, 14 May 2010
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	[[Category:Kernel XIP]]		[[Category:Kernel XIP]]
		+	[[Category:Specification]]

← Older revision		Revision as of 10:13, 14 July 2007
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	*Figure out difference in usage or intent (if any) between use of CONFIG_XIP_ROM and CONFIG_XIP_KERNEL. Determine if the difference in feature set for execution from ROM vs. execution from FLASH (when flash is also used for filesystem operations) means that we should specify these separately.		*Figure out difference in usage or intent (if any) between use of CONFIG_XIP_ROM and CONFIG_XIP_KERNEL. Determine if the difference in feature set for execution from ROM vs. execution from FLASH (when flash is also used for filesystem operations) means that we should specify these separately.
	*Decide if we should standardize use of CONFIG_XIP_PHYS_ADDR vs. CONFIG_XIP_KERNEL_TXTBASE		*Decide if we should standardize use of CONFIG_XIP_PHYS_ADDR vs. CONFIG_XIP_KERNEL_TXTBASE
		+
		+	[[Category:Kernel XIP]]

Kernel XIP Specification R2 - Revision history

Peter Huewe: /* Remaining Issues */

Chris at 10:13, 14 July 2007

Wmat: Legacy Content Conversion