search

tukl-msd / DRAMSys

DRAMSys a SystemC TLM-2.0 based DRAM simulator.
Other
200 stars 53 forks source link

Timing constraints for RFMab #44

Open hritwik567 opened 1 month ago

hritwik567 commented 1 month ago

Hi, I am trying to understand the timing constraints for the RFM command. I was hoping to get some help.

Based on my understanding, this code does not check for timing constraints for RFMab, but it blocks ALL the banks if the RAA Counter of even ONE of the banks is greater than RAAMMT.

Question: Is my understanding of the code correct?

https://github.com/tukl-msd/DRAMSys/blob/caf5845c79a4cd38635ffc1b6e316af65798e1d8/src/libdramsys/DRAMSys/controller/refresh/RefreshManagerAllBank.cpp#L142

lsteiner-tukl commented 1 month ago

Yes, your understanding is correct. The standard says that if RAAMMT is reached, no additional ACT commands are allowed. In order to ensure that the refresh management command can be issued as early as possible, we block all bank machines. The timing constraints are checked in the respective timing checker, not the refresh manager.

hritwik567 commented 1 month ago

What happens if one bank's RAA counter is equal to RAAMMT and the timing constraints of RFMab are not satisfied yet?

Will the Refresh manager block all the banks and wait for timing constraints to be satisfied? Or will it allow other banks to receive ACTs and when the timing constraint is met, issue an RFMab?

I'm trying to understand what the standard means exactly. If RAAMMT is reached, are ACTs not allowed to that particular bank or all the banks?

I would assume ACTs are blocked to only a particular bank and the refresh manager can choose a policy for issuing RFMab. The 2 possible policies being

  1. block all the banks and wait for timing constraints
  2. block a particular bank, wait for timing constraints to be met and then launch RFMab
lsteiner-tukl commented 1 month ago

It will block all banks and wait for timing constraints to be satisfied, yes. If you would allow ACT commands to be issued to other banks, the RFMab would be delayed because it can only be issued if all banks are precharged just like a REFab command. So your second policy does not make much sense.

hritwik567 commented 1 month ago

Understood.

I was just trying to figure out if the ACTs can be launched to other banks.

Thank you very much.