Hi,I have two DDR3 instantiations in my design. I'm low on PLL resources and I need to share the PLL of the two DDR3 inst. In the documentation I saw that the ALTMEMPHY does not support using a shared PLL, and the UNIPHY does. I can't seem to use the UNIPHY for the Arria 2 GX although it is stated that it is supported. Is it possible to share a PLL for two DDR3 instantiations in Arria 2 GX device ? Thank You!
Is it the PLL you're low on or clock outputs? I'm pretty sure a number of the clocks can be shared via assignments. The altmemphy handbook talks about it. But you're right that altmemphy requires two different PLLs for some of the clcoks.
I'm short on PLL's, I have an IP that uses 2 PLL's and is strict and can not be modified.2 DDR3 take 1 PLL each. And I have 16 channel of LVDS that can be used with external PLL. Maybe there is a way to feed the LVDS with the DDR3 PLL outputs ? (LVDS PLL requires an lvds input clock)
16 transmit or receive channels? At what data rate? The dedicated True LVDS silicon requires a PLL on that side(as there is a dedicated, low skew low jitter clock tree from the PLL to the SERDES). This generally doesn't combine with DDR3 since they use a top/bottom PLL. That being said, many applications don't need "True LVDS" and work fine with just a PLL. If you're pushing the limits, say 1GB data rates, you need True LVDS, but otherwise might be all right with the LVDS I/O standard, the I/O's double-data rate registers, and a global clock(driven from a PLL elsewhere in the chip).
16 transmit and receive.The data rate is 500Mbps, it will be implemented using soft LVDS, There is no problem to use 1 external PLL for the LVDS tranceivers. The problem occures when I have no free PLL's at all. Can I derive the LVDS clock inputs from a DDR3 ALTMEMPHY PLL, or is it simply impossible ?
Just to clarify, for the LVDS receive data you're also getting a clock, so that clock would need to drive the PLL. I'm not sure. The PLL operation is pretty independent of the input clock's I/O standard, i.e. if you drove it with LVDS and all the frequencies necessary for DDR3 are available, it should work.How many PLLs in the device you're using? I take it two are used for altmemphy, but wondering what others are used for(if they exist).