Hardware Image Caching - Altera Nios II Embedded Evaluation Kit Cyclone III Edition User Manual

Hardware Image
Caching
Altera Corporation
July 2010
stored in flash, a flash image catalog is kept in CFI flash at offset 0x8000.
The implementation details of this catalog are described in the Hardware
Image Caching section below.
Table B–1. Memory Map of CFI Flash
Flash
0x000000 - 0x007FFF
0x008000 - 0x00FFFF
0x010000 - 0x01FFFF
0x020000 - 0x0FFFFF
0x100000 - 0x17FFFF
0x240000-0x63FFFF
0x640000-0xDBFFFF
0xD00000 - 0xFFFFFF
Copying data from the SD Card to flash is slow due to both the read speed
from the SD Card in SPI mode and the write speed of the CFI flash
However the remote update feature allows us to reconfigure the FPGA
from anywhere in flash, so we can benefit by persistently holding
(caching) a certain number of frequently used application hardware
images in flash to avoid having to copy them from the SD Card every time
the application is loaded.
The Application Selector utility can cache up to 10 application hardware
images in CFI flash. When the user chooses an application to load from
the SD Card using the Application Selector, the Application Selector first
scans through its catalog of hardware images currently stored in CFI flash
to see if any of them match the hardware image being requested. If one of
the images cached in CFI flash does match, the Application Selector
reconfigures from the offset of that cached hardware image instead of
copying the image from SD Card to flash. This significantly reduces the
load time.
Caching the hardware images requires the application selector to be able
to quickly tell if an image in CFI flash is the same as one on the SD Card.
To determine whether a hardware image in flash matches a hardware
image on the SD Card, a 32-bit timestamp value is used as a tag. During
the file conversion process, the sof2flash utility inserts a 32-bit timestamp
in the hardware image .flash file as an S0-type record on the first line of
the file. When the Application Selector is about to load a hardware image,
Size
32K Application Boot Code
32K HW Image Catalog
64K Unused
896K Selector HW Image
512K Selector SW Image
4M Application SW
7.5M Application HW Images
3M Unused
Nios II Embedded Evaluation Kit, Cyclone III Edition
Flash Contents
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B–4