Re: Caches in embedded systems
- From: "DAC" <Mister@xxxxxxxxxx>
- Date: Thu, 4 May 2006 16:55:49 +1000
Hi
I would like to know what sort of caches (Icache and Dcache) do
typical embedded systems use. I know caches are avoided in real time
applications
Only if idiots are programming who dont know what volatile means. Caches are
not an issue in real time systems unless you have multiport memory that
another realtime system is relying on and your system doesnt support the
ability to write through the cache or 'flush out' the cache when requested.
but wondering when they are used what sort of
configuration do they have Directmapped/assoictaivity, what line size
etc, writeback/write through ? That aso leads me to askembedded systems
with caches what sort of applications are they used in. Can any one
give me some examples.
The answer is pretty simply, they are used in any system where clock speed
CPU runs faster than the memory.
Once you pass about 40Mhz you generally see caches starting to come in on
embedded systems. We have some systems that run from 1Mhz to 33Mhz with no
caches and from 66Mhz upto 1Ghz all have caches. They are almost never
direct mapped because the caches on most embedded systems will be 16kb etc
while the main memory could easily be 16MB or more. Usually they have
256/512/1024 byte chunks (it all depends on the CPU and its pointer
registers). Usually you associate a peice of cache to map over the main
memory. A system of oldest section used combined with least section used
decides which cache block to overwrite. Modern caches allow block sizes of
variable size.
.
- References:
- Caches in embedded systems
- From: shrey
- Caches in embedded systems
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