Shared Cache

[AntonioPrioletti]

Hi, I would suggest a problem. I have created an architecture with two processors, and I instanced a cache full privacy for both processors, and then a cache shared by connecting it always full to the first two via a single bus for sharing. Now if I make a call before the main application where a variable x-volatile, then the processor assigns the value 0 3. When I go to read the value of the variable x with the processor 1 this is always 0 and not 3 because the processor 0 has changed. Looking at the address of the variable x that coincides for both variables, then how come I always value 0? :cry:

[AntonioPrioletti]

Sorry, but in precedent post I wrote a really poor english, because I am Italian; now think that it is better.

Hi, I would suggest a problem. I have created an architecture with two processors, and I instanced a full private cache for both processors, and then a shared cache of second level always full, by connecting it with the first via a single share bus. Now a create an example application when I define a volatile variable x, then the processor 0 assigns to it the value 3. When I go to read the value of the variable x with the processor 1 this is always 0 and not 3 though the processor 0 has changed that value in 3. Looking at the address of the variable x in both processor, that coincides, How can i solve this problem, doing so that the processor 1 read value 3 and not 0?

The code is:

volatile int x;

int proc0(int id)
{

printf("Cpu 0, before change x = %d \n", x);
x = 3;
printf("Cpu 0, after change x = %d, with address %p\n", x, &x);
}

int proc1(int id)
{
printf("Cpu 1, before change x = %d, with address %p\n", x, &x);
x = 20;
printf("Cpu 1, after change x = %d\n", x);
}



int main(int argc, char **argv) {

int id = impProcessorId();
printf("CPU %d starting...\n", id);

switch(id) {

case 0:
proc0(id);
break;

case 1:
proc1(id);
break;

case 2:
break;
}

return 1;
}

[DuncGrah]

This is the issue of using writeback rather than write through caches as discussed in this forum posting.