Memory Booting
No
Yes
Copy Image into a Target
RAM
Device is XIP
Type?
Copying Failed
Return Fail
Execute Initial SW
Preliminary
Memory Booting
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21.7 Memory Booting
21.7.1 Overview
The Memory Booting procedure takes care of starting an external code located in memory device types.
These devices are also called permanent booting devices since they are used for booting permanently.
Figure 21-8. Memory Booting
The permanent booting devices supported are:
•
SD cards
•
NOR flash
•
NAND flash
•
SPI EEPROMs
There are two groups of permanent 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 that 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 that 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 is different depending on the
device type:
•
On a GP device type, a booting image is considered to be present when the first 4 bytes word 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.
2000
ROM Code Memory and Peripheral Booting
SPRUGX9 – 15 April 2011
© 2011, Texas Instruments Incorporated
Содержание TMS320C6A816 Series
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