I am doing some benchmarking and I need to clear the cache before each test. I have this example here:
Caches and Self-Modifying Code
However, I just want to clean the whole cache. Is there an easy way to do that? I do not need to know the start and end address of the functions. I just want some simple code
Thanks.
The ARMv7-A/R Architecture gives an example sequence for cleaning the entire data and unified cache, using set/way operations. It's right at the end of chapter B2.2.7 (Cache and branch predictor maintenance operations), under a sub-heading of "Performing cache maintenance operations". My recommendation would to use that code.
If you have DS-5 installed, the "startup_Cortex-A9" example in the Bare-metal_examples.zip includes a version of this code. The difference is the code in the example is doing an invalidate rather than a clean operation. But that is easy enough to change.
I am doing this in user side code. I thought that this was only possible via the clean_cache function. So, running your suggested code will work there too?
Ahh, sorry - I had misunderstood your question. No, you can't directly clean/invalidate the caches from User mode. If you're are running under an OS, you will have to make a call to the OS to have it do it for you.
Which OS are you using?
I am using the Linux Kernel 3.7 on a Altera Cyclone V board.
> The ARMv7-A/R Architecture gives an example sequence for cleaning the entire data and unified cache, using set/way operations
Hmm - this isn't guaranteed to work portably. On a single-core system you'll get away with it, but the set/way maintenance operations are not guaranteed to be SMP-safe. The only "architecturally sound" means to clean/clean-invalidate the cache in an SMP system once it is up and running is use the "by VA" operations.
*EDIT* Also note that by default the data memory allocations returned to an application in Linux is marked "XN" in the MMU (eXecute Never) - the data pages are not executable. IIRC you'll need to make some special memory allocation calls with the kernel to get some executable memory.
HTH,
Pete
So, essentially, I have to use that clean_cache function as in the link in my OP? You wouldn't know of any documentation for that function? Also, I guess I cannot just pass the result of malloc? As discussed here:
How clear and invalidate ARM v7 processor cache from User Mode on Linux 2.6.35 - Stack Overflow
Why is that?
Are you able to say if this is enough to clean the whole cache? Using the example in the OP
uint32_t * code = mmap(
NULL,
32768, // 32kb -- Whole Cache.
PROT_READ | PROT_WRITE | PROT_EXEC,
MAP_PRIVATE | MAP_ANONYMOUS,
-1,
0);
Hi there,
I know that this is an old post, but I have a related question.
I should clean and invalidate the L2 cache on Cortex A9. Can I use your function? Instead of 32768 I will use 512000, the size of L2 cache.
It works?