How to enable performance counters for Rocket core?

[sammy17]

I am trying to enable performance counters in the Rocket core. I don't see the implementation of mhpmevent3, mhpmevent4, mhpmcounter3, mhpmcounter4 in the RTL of the defaultConfig. I see that following parameter is set to true by default but none of the mentioned counters does not get generated in the defaultConfig.

haveBasicCounters: Boolean = true

rocket-chip/src/main/scala/rocket/RocketCore.scala

Line 37 in b503f8a

haveBasicCounters: Boolean = true,

Can someone please explain how to enable these basic performance counters in Rocket?

I tried increasing nPerfCounters: Int = 0 to 8 and using following code to configure and read hpmcounter3. But counter never changed, it had a random value in each run.

addi x14, zero, 0x04
slli x14, x14, 8
addi x14, x14, 2
csrrw zero, mhpmevent3, x14 
...
csrr x28, mhpmcounter3 #Read counters in two different places
...
csrr x28, mhpmcounter3

I am using the configuration mentioned in #1343 (comment)