All,
Correct, I did some math and they almost work out for DDR1 values However into DDR2 clocks speeds it gets increasingly bad.
Going through the SPD tables I have found, it looks like there is not a mathematical way to convert those values, as they are in nanoseconds but only some are actually linear. Some values like 0x3D for spd->clk_cycle can't be converted using a formula, easy enough to put into a case statement. 0x3D is intended to be 3.75ns and 0x30 is 3.00ns. So 0x0D would be 0.75ns? Doesn't work in my book. However 0x25 is a nice easy clear 2.5ns. Whomever put Hex values to represent decimal numbers probably chose a poor idea. I am just hoping that most RAM isn't putting 'exact' values in SPD tables, but rather an industry standard value that is going to work with the intended SODIMM / DIMM, our code should be using lookup tables if so, not math formulas.
I have already written a flat case statement with correct values. Easy to see now why it was breaking, as the CAS latencies were all hosed over for the faster memory.
-Russ
-----Original Message----- From: Bruce_Leonard@selinc.com [mailto:Bruce_Leonard@selinc.com] Sent: Tuesday, June 03, 2008 5:34 PM To: rmcguire@videopresence.com Cc: 'David Hawkins'; 'Steve Hensley'; u-boot-users@lists.sourceforge.net Subject: RE: [U-Boot-Users] 83xx SPD_EEPROM DDR2 Issues
"Russell McGuire" rmcguire@videopresence.com wrote on 06/03/2008 04:15:55 PM:
I haven't gone through the rest yet, but most likely if we want to keep
SPD
working for DDR2, we'll have to add the DDR2 definitions SPD into the
code,
as it looks like the DDR2 port is only partially complete.
-Russ
Russ,
That's pretty much jives with my recollection. One other thing that leaps to mind was the calculation for max_bus_clk. I hand cranked through that with a high clock rate as input and due to rounding errors got a bogus value. I don't remember the details right off the top of my head but it seems to me that the net result was I started with a bus clock that should have landed max_data_rate in one of those if-if-else-if cases, but it didn't. So I think that whole function (and especially the max_bus_clk calculation) needs to be gone through. Good luck. I'd help but I have my own issues with MTD :(.
Bruce