Device Family: Arria® II GX

Device Family: Arria® II GZ

Device Family: Arria® V GT

Device Family: Arria® V GX

Device Family: Arria® V ST

Device Family: Arria® V SX

Device Family: Cyclone® III

Device Family: Cyclone® III LS

Device Family: Cyclone® IV E

Device Family: Cyclone® IV GX

Device Family: Stratix® III

Device Family: Stratix® IV E

Device Family: Stratix® IV GT

Device Family: Stratix® IV GX

Type: Answers

Area: EMIF

Area: Intellectual Property


IP Product: DDR2 SDRAM Controller supporting ALTMEMPHY
IP: LPDDR2 SDRAM Controller with UniPHY

Why is tREFI value in simulation and board measurement different from what is set in Altmemphy and UniPHY based DDR2 SDRAM memory controller?

Description

tREFI result in simulation and on the board might be larger than expected if you set tREFI to less than 7.8us in DDR/DDR2/LPDDR2 MegaWizard.

DDR/DDR2/LPDDR2 SDRAM IP has MEM_TREFI parameter which defines tREFI parameter in terms of memory clock cycles.

Since the minimum value of this parameter is limited to 780, tREFI becomes larger when memory clock is slower.

For example, tREFI for DDR2 SDRAM should be 3.9us at >85C. But if DDR2 memory clock is 125MHz(8ns), minimum tREFI value can be 8ns x 780 = 6.24us.

tREFI for DDR should be 7.8us. But if DDR memory clock is 76.9MHz (13ns), minimum tREFI value can be 13ns x 780 = 10.14us.

Workaround/Fix

As a workaround, if DDR memory clock is below 100MHz or if you set tREFI to <7.8us on DDR2 memory, you can change MEM_TREFI parameter in

*ddrx_controller_wrapper (Altmemphy based IP) file or *_c0 (UniPHY based IP) file to correct tREFI value.

This issue is planned to be fixed in a future version of Quartus® II software.