$ j* U6 E0 ^" y4 ]作者: 2532609929 时间: 2014-9-11 18:55
DDR通过检查最大有效地址来识别容量，具体请看uboot的common/memsize.c文件中的检查代码，也可以看如下：2 A; ~# P4 U& O6 h, @
/*# m' g0 B6 | e8 m: C; a9 |* M
* Check memory range for valid RAM. A simple memory test determines1 J0 c8 F; s: e ]
* the actually available RAM size between addresses `base' and- @9 z* D/ u, r" N
* `base + maxsize'.) C* Y+ _# j1 C9 c" z
*/ 6 k9 X# R0 x2 S% x/ plong get_ram_size(long *base, long maxsize); y2 V8 a- ]1 \: _( N
{ 9 D- D/ }/ F& }# ?& f+ U6 f volatile long *addr; k" J$ _7 ^9 M9 U2 N- ? long save[32]; 5 w0 @0 o" Q; W3 M8 o+ ? long cnt;5 n! X9 ?! W6 s4 {1 R
long val;2 C2 U. A5 q2 S" B A! u7 q
long size; 8 C$ N, a' V6 g3 k% C int i = 0;( g5 X- Z: R7 ?
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for (cnt = (maxsize / sizeof (long)) >> 1; cnt > 0; cnt >>= 1) {/ `1 C* Q3 W8 ]6 d5 D" C
addr = base + cnt; /* pointer arith! */ , H& J6 u* k0 o) L4 } sync (); 8 B0 i- [$ N) ]% P( E2 C8 m save[i++] = *addr;0 Y* Y" u$ h0 ?. g3 U. f& O
sync ();) x* h }9 p2 c
*addr = ~cnt;7 l g0 i- c% Q
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addr = base; 8 I+ ~$ j' b9 `! | sync (); 9 l" a1 J( B0 t& N. E save = *addr;0 X9 {5 G( j$ q4 X0 g6 R( z. @
sync ();7 X% U+ r9 e& z# B
*addr = 0;% Y( \& B) Q2 k: `+ j
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sync (); e0 ?( H, _& h if ((val = *addr) != 0) { ! f" c- g3 @1 W! R! r* n /* Restore the original data before leaving the function.6 o$ r! S; j/ P, N# x% A& Y& y
*/ 5 `; {# R* e" N7 I% k% k sync (); / ~+ r( Y& ], _% s: n( X, l *addr = save;, U/ K2 o+ U q3 j! {1 {
for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) { , G* a. S6 A2 B1 V' b: x( S1 E" L addr = base + cnt; 3 x' g. G$ y. L f' i7 L o- u sync (); * @ R( H. j: }" o( O- N *addr = save[--i]; - N* f5 m3 l% a* V6 P/ S; s1 E }# q; ]/ Z9 F% {" S9 E7 T/ z
return (0);& {; ?! z3 z8 [, ^2 o0 T) R/ E* N
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for (cnt = 1; cnt < maxsize / sizeof (long); cnt <<= 1) { ) E# o! u# Q: \9 H5 Z& R addr = base + cnt; /* pointer arith! */ }3 H$ T5 U* Y4 o0 H, d
val = *addr;0 b: P6 ?& b9 F& I/ Q3 h3 x/ J6 Z
*addr = save[--i]; W2 z1 N3 r0 r if (val != ~cnt) { ( U- X) i% u. F4 Q* b2 X size = cnt * sizeof (long);/ ^; G; h4 @' U; C
/* Restore the original data before leaving the function. & J* J% ]: U+ a$ ^4 p- Y' Y */. e! f" h) }2 n( s
for (cnt <<= 1; cnt < maxsize / sizeof (long); cnt <<= 1) {/ O, W# @% s- b: L& G* t, _1 y
addr = base + cnt; p7 u# R l" `, c3 \) J0 m- R4 E
*addr = save[--i]; / ]/ t6 l* f w T' h% X6 T }7 X3 n" Q- D+ F) j ?/ Q% F; c9 D
return (size);3 ?3 F# J3 q# z
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} 6 Q4 }6 }1 V, O9 C* d& k 8 B- Z* ?0 C* s7 d: R* j8 t return (maxsize); * g2 }- L2 l* z& U5 H& |( v8 F} 3 t/ h5 L' b; F. r5 Z; B- {int dram_init(void): m b6 o) c! m) F$ P7 v. N* q
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/* dram_init must store complete ramsize in gd->ram_size */: C5 ~& d$ q! A; [
gd->ram_size = get_ram_size( 0 g8 X& G5 a' j7 l (void *)CONFIG_SYS_SDRAM_BASE, ( C" O3 d" i1 I3 A% V, P$ P2 @$ C CONFIG_MAX_RAM_BANK_SIZE); N9 l" u( H& d) O% X return 0; % x& D$ L% Z. Z2 E" d2 d( m' ?5 g}7 r8 R; w& ^3 w0 A# C
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FLASH是通过检查FLASH内部的ID识别容量，希望对您有帮助！ & y, h$ m7 t$ H' p0 \3 m7 m$ Q1 [/ f
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