hi,
El Tue, Dec 08, 2009 at 09:33:18PM +0100 Wolfgang Denk ha dit:
> After relocation we have a full-blown, "normal" C runtime environment.
> Before that, you can use C as well, if you mind the restrictions (like
> data and bss not being available/writable yet, no real stack, etc.).
as suggested i reimplemented the flash, pll and sdram initialization
in C, what is working so far.
now i am trying to reimplement the lowlevel_init() function in C. this
seems to be an easy task, but gcc insists to use the stack, which
isn't set up at this point
the C implementation is:
void lowlevel_init(void)
{
red_LED_on();
green_LED_on();
/* Configure flash wait states before we switch to the PLL */
flash_cfg();
/* Set up PLL */
pll_cfg();
green_LED_off();
/* Setup SDRAM */
sdram_cfg();
green_LED_on();
red_LED_off();
/* FIXME: we use async mode for now */
__asm__ __volatile__("mrc p15, 0, r0, c1, c0, 0\n"
"orr r0, r0, #0xc0000000\n"
"mcr p15, 0, r0, c1, c0, 0");
}
which results in the following machine/assembly code:
c1f01094 <lowlevel_init>:
c1f01094: e52de004 push {lr} ; (str lr,
[sp, #-4]!)
c1f01098: e24dd004 sub sp, sp, #4 ; 0x4
c1f0109c: ebffffe4 bl c1f01034 <red_LED_on>
c1f010a0: ebffffef bl c1f01064 <green_LED_on>
c1f010a4: eb00483d bl c1f131a0 <flash_cfg>
c1f010a8: eb004842 bl c1f131b8 <pll_cfg>
c1f010ac: ebfffff2 bl c1f0107c <green_LED_off>
c1f010b0: eb004852 bl c1f13200 <sdram_cfg>
c1f010b4: ebffffea bl c1f01064 <green_LED_on>
c1f010b8: ebffffe3 bl c1f0104c <red_LED_off>
c1f010bc: ee110f10 mrc 15, 0, r0, cr1, cr0, {0}
c1f010c0: e3800103 orr r0, r0, #-1073741824 ;
0xc0000000
c1f010c4: ee010f10 mcr 15, 0, r0, cr1, cr0, {0}
c1f010c8: e28dd004 add sp, sp, #4 ; 0x4
c1f010cc: e8bd8000 pop {pc}
is there a way to convince the compiler not to use the stack, or is it
for some reason impossible to translate this routine to C without
having a stack?
kind regards
--
Matthias Kaehlcke
Embedded Linux Developer
Barcelona
The salvation of mankind lies only in making everything the concern of all
(Alexander Solzhenitsyn)
.''`.
using free software / Debian GNU/Linux | http://debian.org : :' :
`. `'`
gpg --keyserver pgp.mit.edu --recv-keys 47D8E5D4 `-
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