On Tue, Mar 20, 2012 at 8:55 AM, Werner Almesberger <[email protected]>wrote: > > > - nitpicking: the official names of pins 20 and 47 of U14/U15 are > LDM/UDM, not LDQM/UDQM >
Nice catch :-) applied temporarily to: http://downloads.qi-hardware.com/people/adam/m1/tmp/m1r4/SDRAM_20120320.pdf > > - the DRAM data sheet [1] says the -5B version (which is what we > have) needs Vdd = VddQ = 2.6 +/- 0.1 V for DDR400 operation. If > operating at a lower speed, it is content with 2.5 +/- 0.2 V. > yeah, I have had the same question too when I firstly reviewed it. :-) http://lists.milkymist.org/htdig.cgi/devel-milkymist.org/2010-January/000360.html > > Do we plan to operate the DRAM in M1r4 at DDR400 speed ? If > yes, we should consider raising the voltage. > I don't know if next generation will apply or not. But Sebastien has replied it with reasons below: http://lists.milkymist.org/htdig.cgi/devel-milkymist.org/2010-January/000368.html > > 2.5 V is also supplied to the JTAG board and to the FPGA. The > FPGA (I/Os are configured as SSTL2_I for DRAM, TBD for the > revision) should have no issue with raising the voltage to > 2.6 V. Not sure about the JTAG board. > This is good topic to keep an eye on that when a new generation/proposal came out. > A data point for the termination resistors: Micron recommend to > place them halfway between sink and source. (Page 11 of [2], > and the theory is on page 4 of [3].) Note sure how picky we > have to be given the relatively short distance between FPGA and > DRAM. I'd be a bit more concerned about matching trace lengths. > I don't know how M1 implemented this in practically. There's initial great thread "PCB layout instructions" by Sebastien: http://lists.milkymist.org/htdig.cgi/devel-milkymist.org/2010-January/000374.html "the FPGA's IODELAY elements to compensate for signal propagation delay discrepancies, and, contrary to length-equalizing (and length-increasing) zigzags, they do not cause additional signal integrity issues (ringing, noise, etc.)" It's real quite new fun when I've firstly heard even traditional here layout guys who can't imagine how it unbelievably works then. Uwe Bonne has posted/concerned with similar questions: http://lists.milkymist.org/htdig.cgi/devel-milkymist.org/2010-February/000398.html Sebastien maybe have idea provided to you. :-) > > I also had a brief look at the NOR and didn't find anything > suspicious there. > Thanks, - adam
_______________________________________________ http://lists.milkymist.org/listinfo.cgi/devel-milkymist.org IRC: #milkymist@Freenode
