RE: [U-Boot-Users] Generic ARM Error with respect to usage of r8 in start.S's.
Let me restate my minor point hopefully more correctly. - gd/r8 is only used to reference things in the gd_t structure and its members. Given the way things currently stand for ARM something like the following might work as well and free up a register and remove an assembly dependency:
#define DECLARE_GLOBAL_DATA_PTR gd_t *gd = &global_data -------------
gd_t global_data; /* global data declaration */
start_armboot() { #include <someheader with extern gd_t global_data> /* remove stack allocation of global */ }
I'm NOT saying that I think this is needed.
As far as a patch goes maybe (though I can't test on anything other than arm925), the one touchy point I noticed when looking at the code was the partially useful (in a forward looking way) "irq handling code" would have to regress or be redone to be made to work with the current level of the overall code.
Regards,
Richard W.
-----Original Message----- From: Wolfgang Denk [mailto:wd@denx.de] Sent: Tuesday, June 24, 2003 3:29 PM To: Woodruff, Richard Cc: u-boot-users@lists.sourceforge.net Subject: Re: [U-Boot-Users] Generic ARM Error with respect to usage of r8 in start.S's.
In message FD2AC9A020DDD51194710008C7089B20053D4CAD@dlee17.itg.ti.com you wrote:
The u-boot for ARM code defines and uses global data which is not referenced using r8 (can be seen by all). The code as currently generated only uses r8 to access into the bd_info structure and its members. As it is, the bd_info
No. All access to the "global data pointer" ("*gd") goes through r8, as defined in "include/asm-arm/global_data.h":
#define DECLARE_GLOBAL_DATA_PTR register gd_t *gd asm ("r8")
structure is allocated on the C stack in start_armboot(), there is nothing special about the sdram which its allocated in.
The structure
could have as
As mentioned before, the ARM initialization sequence and memory map do not exactly fit into the U-Boot model as it was intended to be. The curerent state is a result of the port done for the ARMBoot project, but this is a temporary state which will be fixed in a future release.
Yes the flexibility to do different things is there which is good, unfortunately the leaving of expansion hooks which break
the existing
code somewhat defeats its usefulness.
The problem is that we obviously missed the exception code when chosing r8. If you can, please submit a patch to fix this problem.
Best regards,
Wolfgang Denk
-- Software Engineering: Embedded and Realtime Systems, Embedded Linux Phone: (+49)-8142-4596-87 Fax: (+49)-8142-4596-88 Email: wd@denx.de In an organization, each person rises to the level of his own incom- petency - The Peter Principle
In message FD2AC9A020DDD51194710008C7089B20053D4CB2@dlee17.itg.ti.com you wrote:
Let me restate my minor point hopefully more correctly. - gd/r8 is only used to reference things in the gd_t structure and its members. Given the way things currently stand for ARM something like the following might work as well and free up a register and remove an assembly dependency:
But this is exactly what I want. The "global data" pointer (which used to be calles "initial data pointer") is meant for some data which is needed globally (i. e. cannot be put on a stack) and may be used before the initialization of SDRAM.
The current implementation of the init sequence is not in the philosophy of U-Boot. It may be changed. Maybe soon.
The design goal is to switch to C code as soon as possible, and implement as much as possible in C - including for example the initialization of the memory controller.
Best regards,
Wolfgang Denk
participants (2)
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Wolfgang Denk -
Woodruff, Richard