Regular Contributor
Posts: 23
Registered: ‎05-30-2009

DDR2 clock frequency



In the User guide it is said that the DDR2 micron component is running in 133mhz, but opening edk project I see that the signal DDR2_SDRAM_MPMC_CLK_S is actually a 125mhz clock


My questions:

1. If i am using mig for that device, should i choose 125mhz frequency and bot 133 because i cannot produce a 133mhz clock from my dcm?


2. If i want to choose anothe ddr2 component, for example a ddr2-667 (333mhz) will i still be able to operate it with MIG, at the maximux frequency the spartan can work with? (166mhz)




Avnet Employee (Star Contributor)
Posts: 471
Registered: ‎04-16-2009

Re: DDR2 clock frequency



Here is an answer I got from the board designer:




For a -4 Spartan-3x FPGA, 133 MHz is the max frequency supported from MIG.  A -5 supports 166 MHz.  If he only has a -4 device, he can't simply upgrade the memory device and get a faster speed.  There are two sides of this interface, so he needs to look at both.
Furthermore, if he is using MicroBlaze, there are practical limits to how fast MB can run as well.  The standard, asynchronous setup for MPMC has the MB clock at 1/2 the MPMC clock.  So, to run his memory at 166 would require him to run his MB at 83.3 MHz, which is probably not possible with a standard set of peripherals.
The 1800A board was designed with a 125 MHz native input clock since that is the minimum operating frequency for DDR2.  This puts MB running at 62.5 MHz.  You could swap out the 125 MHz for 133 or maybe even use the DCM to synthesize 133.  This puts the MB clock at 66.7 MHz, which is a stretch, but still possible.