Könnte es damit zu tun haben, daß ein bestimmter geschützter Bereich für
Bootloader existiert und daß dieser, um verschiedene
Prozessorarchitekturen zu unterstützen, entweder an den Anfang oder ans
Ende des Adressraumes des ROMs gepackt wird.
Da aber der von Dir genutzte Controller über sein eigenes ROM verfügt,
wirst Du die Boot-ROM-Funktion des externen Flashs kaum nutzen wollen.
Also ist's egal.
Zitat Spansion:
For boot devices, the first or last 64-Kbyte sector is subdivided into
several smaller sectors. Two typical configurations of these smaller
sectors are 1-16 Kbytes, 2-8 Kbytes, 1-32 Kbytes and 8-8 Kbyte sectors.
These smaller sectors are generally used to store boot code or
parametric data. The reason for this is that boot code and parametric
data usually do not require a whole 64-Kbyte sector, but still need to
be placed in a separate sector so it can be properly protected or
changed without affecting other portions of code. Smaller boot sectors
permit this without having to waste an entire 64-Kbyte sector. Boot
sectored devices also have the option of placing the smaller boot
sectors within the first 64 Kbytes of the low address range (called
bottom boot) or the last 64 Kbytes of the high address range (called top
boot).
This is due to the way in which microcontrollers access the boot code
after power-on.
Two conventions for microcontrollers exist:
1. Top-boot convention, where the first address fetch after power-on is
performed at the top of the memory space (FF...FF0h). Microcontrollers
based on AMD® and Intel® X86 architecture processors boot from the top
of the memory space.
2. Bottom-boot convention, where the first address fetch is performed at
the bottom of the memory space (00...000h). Microcontrollers based on
IBM®, RISC, and Motorola® processors boot from the bottom of the memory
space
