> This is not quite right. If you enable ODT, then the 'zq' settings are > taken into use to configure the impedance. And the 0x7b (or 123 in the > decimal format) is just the default reset value for the hardware > register. It does not seem to make much sense, because it is pretty far > away from the generally recommended impedance settings: > > http://www.altera.com/literature/hb/external-memory/emi_plan_board_ddr2.pdf > My understanding is that the 123 value has about the same meaning as > 0xbadf00d or 0xdeadbeef, in the sense that they had to have some kind > of default and they picked a nonsensical magic constant. I think that I > have mentioned this to you in the irc chat earlier: > http://irclog.whitequark.org/linux-sunxi/2014-08-24#9976940
Thanks for spotting this. To be honest, the A13-MID settings were simply known to work on that TZX board, so I just moved them to a generic name and didn't rewrite any of it. The dram settings I get out of meminfo are a bit different (lower dram clk and odt_en disabled). dram_clk = 384 dram_type = 3 dram_rank_num = 1 dram_chip_density = 4096 dram_io_width = 16 dram_bus_width = 16 dram_cas = 9 dram_zq = 0x79 dram_odt_en = 0 dram_tpr0 = 0x42d899b7 dram_tpr1 = 0xa090 dram_tpr2 = 0x22a00 dram_tpr3 = 0x0 dram_emr1 = 0x4 dram_emr2 = 0x10 dram_emr3 = 0x0 > More likely than not, if this configuration is really taken into use, > then the DRAM reliability will become worse. > > Luckily, the .odt_en settings are inert and have no effect on the A13 > hardware when used in the https://github.com/linux-sunxi/u-boot-sunxi/ > bootloader, as explained in: > https://patchwork.ozlabs.org/patch/375959/ That is good to know. > We just need to be really careful when moving all these piles of > nonsensical junk DRAM settings to the mainline u-boot. Would you advise reducing the dram clk to 384 instead of 432 in addition to disabling odt? 432 seems to work just fine, even when running a full xfce environment. -- Paul Kocialkowski, Replicant developer Replicant is a fully free Android distribution Website: http://www.replicant.us/ Redmine: http://redmine.replicant.us/
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