topic Re: dcbf instruction use issue in Qonverge

dcbf instruction use issue

quenreyn — Tue, 20 Mar 2018 08:37:41 GMT

Hi,

I used dcbf instruction to flush my data cache, but it seems that it did not work (I verified via a probe the content of the data cache).

In C, I created a variable:

int i = 0;

// then I call the next routine

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

which is in assembly langage:

# 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

isync

msync

blr

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,

Quentin Reynard

Re: dcbf instruction use issue

alexander_yakov — Wed, 21 Mar 2018 03:40:55 GMT

You said: "I verified via a probe the content of the data cache"

Please submit a screenshot of data cache contents, including cache tags, for two cases - before and after dcbf instruction execution.

Have a great day,
Alexander
TIC

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Re: dcbf instruction use issue

quenreyn — Wed, 21 Mar 2018 08:32:27 GMT

Ok, I will do that.

Can you tell me if the parameter given to the function are ok ?

Thank you,

Quentin Reynard.

Re: dcbf instruction use issue

alexander_yakov — Thu, 22 Mar 2018 15:01:38 GMT

I do not see anything obviously incorrect in your code.

Re: dcbf instruction use issue

quenreyn — Tue, 27 Mar 2018 07:52:04 GMT

My fundamental issue was that the address given to dcbf was not in cache.
The reference manual says:

Perform reads to any 48 Kbyte region, THEN execute dcbf instruction

I now am searching for how to read the L1 data cache !