I pretty much agree with the responses posted so far.

Internal memory is a lot easier to deal with (compilers can keep track of
addresses, etc.). In one project where I need several large buffers
(fetching XML, parsing, and putting results in output FIFOs for
transmission), I use a 1MB external parallel RAM. I also use SPI flash in
several projects (these are 2MB parts). They hold Unifont bitmaps for
displays, hold logging data, and hold system configuration data.

I have not used SPI RAM. In general, I have not seen any that are large
enough. There also would be speed issues when compared with parallel RAM.
It would, however, be really nice to have external SPI memory (flash or
RAM) that was integrated into the chip's memory map. If the
microcontroller also had cache RAM, speed could be pretty quick. For stuff
that has to run fast (and cannot afford a cache miss), a separate memory
section (in a separate address range in the memory map) could be set aside
as internal RAM or flash.

The SPI flash chips I'm using have a bus speed of 75MHz, so you can read
them pretty quickly (but not as fast as internal flash).


Harold




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