Any explanation of APPLYCFG bit of SDRAM control register in Cylcone V

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I have been working on transferring data from HPS SDRAM to FPGA on DE1-SoC board. 

  I followed the steps here    https://www.google.co.kr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahukewjfsrb6_9blahuknqykhyb-cu0qfggemaa&url=https%3a%2f%2fsupport.criticallink.com%2fredmine%2fprojects%2fmityarm-5cs%2fwiki%2fimportant_note_about_fpgahps_sdram_bridge&usg=afqjcnfmofydbjmwmi-oggurnwcf9rqpxq&sig2=tetruarogxnoqeuuaejurg&bvm=bv.117218890,d.dgy   well the transferring works fine, but I do wonder about that applycfg bit from staticcfg register    according to the Cyclone V manual(link below), (SDRAM controller subsystem -> SDRAM contorller address map and register definitions -> staticcfg -> applycfg bit)  description of staticcfg register (which contains applycfg bit) : the register controls configuration values which cannot be updated during active transfers. First configure the membl and eccn fields and then rewrite these fields while setting the applycfg bit. the applycfg bit is write only   description of applycfg bit : "write with this bit set to apply all the settings loaded in SDR registers to the memory interface. This bit is write only and always returns 0 if read "   https://www.google.co.kr/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&ved=0ahukewizpu-zgnflahubgqykhudha5mqfggwmam&url=http%3a%2f%2fpeople.ece.cornell.edu%2fland%2fcourses%2fece5760%2fde1_soc%2fcv_5_hps_tech_ref.pdf&usg=afqjcng38nqwct9e84zvraaafr7ros0qwq&sig2=xcnrp3ndwbnvn8d2eiqd6w&bvm=bv.117218890,d.dgy     I understand like this : any modifications of sdr register(SDRAM controller registers) are not applied to sdram configuration until applycfg bit is set.    but I'm not sure about this because as a matter of fact when I modifed the fpgaportrst register(which is also one of sdr registers), the modification did effect to    sdram configuration, though I didn't set applycfg bit.    so does anybody have experience about anything related to applycfg bit?? what exactly configuration does applycfg bit do??    I see that u-boot run command sort of "go $fpga_apply" to set applycfg bit.. I guess it is part of initialization ..     anything else???