Memory Booting
No
Yes
Copy Image into a target
RAM
Device is XIP
type?
Copying failed
Return fail
Execute Initial SW
Functional Description
26.1.7 Memory Booting
26.1.7.1 Overview
The memory booting procedure takes care of starting an external code located in memory device types.
Figure 26-8. Memory Booting
There are two groups of memory booting devices distinguished by the need of code shadowing. The
code shadowing means copying a code from a non-directly addressable device into a location (typically a
RAM area) from where the code can be executed. Devices which are directly addressable are called
eXecute In Place (XIP) devices.
The Memory Booting flowchart is shown in
. The second step is about performing the
shadowing of the image that is copying the image from external mass storage (non-XIP) into internal
RAM. Failure in image copy results in Memory Booting returning to the main booting procedure which will
select the next device for booting. The next sections detail procedures for device initialization and
detection in addition to the description of the sector read routine for each supported device type. A sector
is a logical unit of 512 bytes.
The detection of whether an image is present or not on a selected device depends on the first few bytes.
On a GP Device type a booting image is considered to be present when the first four bytes of the sector is
not equal to 0000 0000h or FFFF FFFFh.
During the first read sector call, sectors are copied to a temporary RAM buffer. Once the image is found
and destination address is known, the content of the temporary buffer is moved to the target RAM location
so it is needed to re-read the first image sector. On a GP Device the GP header is discarded, therefore
only executable code is located in RAM with the first executable instruction located at the destination
address.
The Image authentication and execution is detailed in
. For more information about image
formats and contents, see
MMC/SD cards and NAND devices can hold up to four copies of the booting image. Therefore the ROM
Code searches for one valid image out of the four if present by walking over the first four blocks of the
mass storage space. Other XIP devices (NOR) use only one copy of the booting image.
4114
Initialization
SPRUH73H – October 2011 – Revised April 2013
Copyright © 2011–2013, Texas Instruments Incorporated