[uClinux-dev] Build SMP uClinux on NIOS II processors

Michael Schnell mschnell at lumino.de
Mon Feb 16 03:56:29 EST 2009

> You can tell Linux to explicitly flush cache lines, so that you don't
> need consistency in hardware.  You only need cache line flushing
> instructions, which is simpler hardware.
How would this work if two user programs share a common memory area ?

I suppose, the kernel needs to maintain some commonly used areas for 
inter-task communication etc. If all of them are defined as 
non-cacheable, I suppose this might slow down the system greatly in 
appropriate applications.
> You need those instructions anyway if you have peripherals doing DMA
> to main memory, so you might not need any changes to the hardware cache.
Right you are. With NIOS hardware this is exceptionally easy, as just 
setting address bit 31 marks the access as non-cacheable. The NIOS 
Kernel of course provides the standard macros to make used of this.


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