When do you need to flush icache?

Hi doleksy,

> I am a bit confused on when I need to flush the icache.

You should invalidate the appropriate icache line before executing its code

whenever the cache is no longer coherent. For example, if you load an

S-Record into memory that contains executable code, you should invalidate

the associated icache lines before attempting to execute newly loaded

code -- otherwise you might execute the old code that is still resident

in the cache.

> I've looked at u-boot and it seems to flush the icache after every srec

> record has been written to memory. Is this overkill?

No -- it's just the strategy chosen by u-boot. Since an srec file does not

include any information on whether or not the new data is executable

code or not, u-boot makes a conservative assumption: it assumes each

srec contains both executable code and data ... and invalidates the

icache and flushes the dcache immediately after decoding and writing

the srec to memory.

Since u-boot can load individual S-Records, it must invalidate/flush the

caches as each record arrives -- otherwise you would always need an end

record (to know when to flush everything).

> As long as you aren't running the new code yet it seems like you could just

> call alt_icache_flush_all when you are finished.

This would work fine.

Regards,

--Scott