topic Re: Cache L1 address retrieving and flush in P-Series

Cache L1 address retrieving and flush

quenreyn — Tue, 13 Mar 2018 10:25:55 GMT

Hi everyone,

I want to flush the L1 cache on my P2020 processor with the assembly instruction dcbf. In order to do that, I need to know where the cache L1 is (if I am not mistaken ?). But I don't find any L1 cache definition in my project and I was wondering if this is why I don't know the address or if this is kind of an automatic process made by the processor ?

Anyway, how can I retrieve the address of the L1 cache ?

Once retrieved, in order to flush it, I will do something like that:

code
# r1 = start of shared region # r2 = end of region loop: dcbf 0,r1 # flush line at address r1 addi r1,r1,<line size in bytes> # point to next line cmpw r1,r2 # finished? ble loop

code

# r1 = start of shared region
# r2 = end of region

loop:

dcbf       0,r1                                  # flush line at address r1
addi       r1,r1,<line size in bytes> # point to next line
cmpw    r1,r2                                 # finished?
ble         loop

Is it the rigth manner to proceed ?

Thank you a lot for your answers,

Regards,

Quentin Reynard

Re: Cache L1 address retrieving and flush

quenreyn — Tue, 13 Mar 2018 15:04:50 GMT

I read this L1 D-Cache Flushing , it helps a bit about L1 cache organisation

Re: Cache L1 address retrieving and flush

adeel — Wed, 14 Mar 2018 09:29:47 GMT

The cache addresses are setup by U-Boot and L1 is used to execute first stage boot loader. Anyway, if I may ask why do you want to flush L1 with your code? OS should take care it.

Re: Cache L1 address retrieving and flush

quenreyn — Wed, 14 Mar 2018 10:34:54 GMT

Unfortunately, I needed to remove U-boot.

I need to flush L1 D-cache before writing into the flash memory to maintain coherency in the memory.

Re: Cache L1 address retrieving and flush

quenreyn — Wed, 14 Mar 2018 15:54:34 GMT

Finnaly I understood that implementing the code from my first question was enougth to flush the entire D-cache.

Re: Cache L1 address retrieving and flush

quenreyn — Mon, 19 Mar 2018 08:46:26 GMT

Ok, so after some verification with my probe, the routine does not work, I don't see my D-cache as totally flushed and invalidated.
I think I made a mistake while giving the argument to the dcbf instruction.

In C, I created a variable:

int i = 0;

// then I call the next routine (which is exactly the routine from my first message (with isync and msync at the end))

FlushDataCache((int)&i, (int)(&i + DATA_CACHE_FLUSH_48K/4));

I thought the dcbf instruction will find the D-cache according to i variable, and flush the line. I don't know what's wrong ?

Sorry to bother, thank you for your anwsers,

Regards,

Quentin Reynard.