Of all the gin joints in all the towns in all the world, Fernando J V da Silva had to walk into mine at 12:32:44 on Monday 03 March 2014 and say:
> Hi all! > > I've been porting an UEFI application for an ATOM IA32 processor (32 > bits) but I've > a question regarding memory: Is it possible to access more than 4GB of > memory in a 32 bit UEFI application? (Physical Address Extension). > > If so, what is the most appropriate way to point to a address above > 4GB? (BTW, any pointer in 32 bit couldn't directly access anything > beyond 4GB, so how could I behave in this case?). The general answer to this is that you need to create a temporary mapping using the MMU. Your pointers are always limited to 32-bits -- meaning you can never access more than 4GB of address space at a time -- but you can set up page table entries such that a portion of the 32-bit virtual address space is translated to a physical memory region beyond 4GB. Basically this creates a window into the extended memory. You can "slide the window" to access different regions, if necessary. As to whether or not you can do this in a UEFI application, I *think* you can, using the gBS->AllocatePages() and gBS->FreePages() boot service APIs. These allow you to allocate pages at a specific EFI_PHYSICAL_ADDRESS, which is 64 bits wide on both 32-bit and 64-bit UEFI builds. These services are documented in the UEFI specification. Tread carefully. :) -Bill > Thanks in advance! > > Fernando J V da Silva > > --------------------------------------------------------------------------- > --- Subversion Kills Productivity. Get off Subversion & Make the Move to > Perforce. With Perforce, you get hassle-free workflows. Merge that > actually works. Faster operations. Version large binaries. Built-in WAN > optimization and the freedom to use Git, Perforce or both. Make the move > to Perforce. > http://pubads.g.doubleclick.net/gampad/clk?id=122218951&iu=/4140/ostg.clktr > k _______________________________________________ > edk2-devel mailing list > edk2-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/edk2-devel -- ============================================================================= -Bill Paul (510) 749-2329 | Senior Member of Technical Staff, wp...@windriver.com | Master of Unix-Fu - Wind River Systems ============================================================================= "I put a dollar in a change machine. Nothing changed." - George Carlin ============================================================================= ------------------------------------------------------------------------------ Subversion Kills Productivity. Get off Subversion & Make the Move to Perforce. With Perforce, you get hassle-free workflows. Merge that actually works. Faster operations. Version large binaries. Built-in WAN optimization and the freedom to use Git, Perforce or both. Make the move to Perforce. http://pubads.g.doubleclick.net/gampad/clk?id=122218951&iu=/4140/ostg.clktrk _______________________________________________ edk2-devel mailing list edk2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/edk2-devel
