Thanks for your help I will study up on this more and get back with more questions next week! thanks for your help.. BTW I just bought an eprom programer off EBAY it will take quite some time to ship it from china, so i am making baby steps.. :)
> Date: Thu, 30 Jun 2011 12:17:46 +1000 > Subject: Re: more U-boot for Pentium > From: [email protected] > To: [email protected] > CC: [email protected] > > On Thu, Jun 30, 2011 at 12:08 PM, Raleigh Boulware > <[email protected]> wrote: > > > > > >> Date: Thu, 30 Jun 2011 11:58:55 +1000 > >> Subject: Re: more U-boot for Pentium > >> From: [email protected] > >> To: [email protected] > >> CC: [email protected] > >> > >> On Thu, Jun 30, 2011 at 11:54 AM, Raleigh Boulware > >> <[email protected]> wrote: > >> > > >> > > >> >> Hi Raleigh, > >> >> > >> >> On Thu, Jun 30, 2011 at 11:16 AM, Raleigh Boulware > >> >> <[email protected]> wrote: > >> >> > I have been going through the code and I have stumbled accross a file > >> >> > called > >> >> > sc520_car.S that has something called Cache as ram. I am guessing > >> >> > that > >> >> > this > >> >> > is something special for the sc520 correct? Why was there a need to > >> >> > do > >> >> > this? > >> >> > Why was the Cache used like ram in the boot process? > >> >> > >> >> Cache-As-RAM allows the CPU cache to be used as regular RAM while > >> >> U-Boot > >> >> is running from Flash before the onboard SDRAM has been initialised. > >> >> This > >> >> allows a temporary stack, and therefore C runtime environment to be > >> >> created. This this allows you to write the SDRAM initialisation code in > >> >> C > >> >> which is a lot easier than assembler. > >> >> > >> > So this is pnly used if we want to setup the SDRAM controller in C code > >> > >> More that just that - It is used for the duration of board_init_f() which > >> may include all manner of peripheral initialisation prior to relocating > >> U-Boot into RAM. > > Is it possible to just set up the DDR controller early in the process in > > assembler to avoid doing a Cache as ram? The reason I ask is because I might > > have trouble getting other mother boards to do this. > > Yes, you can setup the SDRAM controller in assembler. This would occur in > place of the Cache-As-RAM init you see for the sc520. You also need to > determine the memory size while you are at it (at a pinch, you can hard- > code the memory size initially) > > > > > Als I was looking at 2 rutines. board_init_r() and board_init_f(). It > > appears that the code goes from assmbler to this board_init_f() then back to > > assembler then to board_init_r(). I am not sure of the reason for this. > > board_init_f() runs from Flash - It is responsible for getting everything > setup ready to run U-Boot from RAM. The last thing board_init_f does is > copy U-Boot from Flash into RAM and perform the relocation fixups. > board_init_f() then calls back into assembler at which point a new stack > is created in RAM before jumping to the in-RAM copy of board_init_r(). > Once inside board_init_r(), the Flash is never again accessed unless you > save the environment or erase it and write a new U-Boot binary (i.e. you > can physically remove the Flash chip and U-Boot will still run fine) > > Regards, > > Graeme
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