11.2.10. Series of Reads or Writes
The case shown in the second figure in the "Bank Management Efficiency" topic demonstrates that a read performed from the same row takes only 14.5 clock cycles to transfer data, making the controller 27% efficient.
Do not perform random reads or random writes. When you perform reads and writes to random locations, the operations require row and bank changes. To change banks, the controller must precharge the previous bank and activate the row in the new bank. Even if you change the row in the same bank, the controller has to close the bank (precharge) and reopen it again just to open a new row (activate). Because of the precharge and activate commands, efficiency can decrease by as much as 3–15%, as the controller needs more time to issue a read or write.
If you must perform a random read or write, use additive latency and bank interleaving to increase efficiency.
Controller efficiency depends on the method of data transfer between the memory device and the FPGA, the memory standards specified by the memory device vendor, and the type of memory controller.
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