--- crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68
On Tue, Mar 7, 2017 at 2:07 PM, Hrvoje Lasic lasich@gmail.com wrote:
impedance is function of width of line (with some adjustment of copper thickness) plus thickness of prepag directly below surface where your lines are. So, you need to compare what is on your last pcb and what is on your new pcb. best software to calculate this value is polaris and you can get some days for free if you ask for code but there are free alternatives out there like Saturn that we use. Beside that there are differential lines that you also need to match impedance. I am not sure but I doubt that via registers you can fix this problem.
http://linux-sunxi.org/A10_DRAM_Controller_Calibration#Impedance_settings.2C...
apparently ZQ config registers do exactly that
also, in some cases you can put resistors in series of lines where you think you have problem.
yyyeah not in this case - there's not enough space between the rk3288 and the ddr3 ram ICs to fit 20 0402 resistors, even if i used 4-packs. i'd need to completely redo the entire DDR3 layout and that's something that i know will cost about 4 or 5 revisions (and around $10k in the process).
basically, you need to find out what impedance need to be and where are you now in order to fix this, of course if this is really problem.
yeah i will be checking the PMIC output voltages with a scope tomorrow. it's fairly certain that it's impedances - going from 290 to 300mhz really should not make a huge difference but it does.
l.