On Mon, Jan 03, 2011 at 12:14:39AM -0500, Corey Osgood wrote: >On Sun, Jan 2, 2011 at 8:03 PM, Roger <[email protected]> wrote: >> I've read over the src/northbridge/intel/i440bx/raminit.c, but am still a >> little mystified on setting the settings. >> >> I can see where settings are set to zero (or default), but when I look at >> other >> settings, the values don't seem to match up to what is well documented within >> the comments. >> >> A good easy example would be setting DRAMC: >> DRAMC, 0x00, 0x08, >> >> Is the "0x00" designated by "000" as documented? Hex? >> >> What does "0x08" mean? > >See sdram_set_registers(). Those values aren't written directly to the >register, because there may be some data stored in other bits that we >don't want to lose. So, for DRAMC, sdram_set_registers reads the value >of the DRAMC register (defined in i440bx.h as 0x57), then does a >logical AND with the first value, 0x00 (which will actually clear all >the bits), then performs a logical OR with the second value, 0x08, >which sets bit 3 to 1, indicating the memory type is SDRAM. It then >writes that value back to the register. In situations like this, gcc >should just optimize the whole thing down to writing 0x08 to the >register, so there's no problem with wasting CPU/IO cycles performing >unnecessary functions.
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