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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：
* e9 \& y) {: R4 D, A2 l/*
, ?0 j3 z9 Q/ y. B& K* Check memory range for valid RAM. A simple memory test determines
* z4 f) v' L/ \* the actually available RAM size between addresses `base' and9 j7 Q6 P, G4 k( M8 z4 H
* `base + maxsize'.8 N4 S" w( }' ~& [, p: B
*/' N/ \7 k7 R, u# H7 u: B
long get_ram_size(long *base, long maxsize)
8 u8 _& _8 W/ i' {1 ~8 K3 C{
/ K# M) x' O& Q volatile long *addr;
# z1 `( R" r% H+ |& G+ K% J1 H8 h* s long save[32];' @5 f8 g+ v, q4 Z5 N
long cnt;
' z" s0 t% T# K" [: q long val;- a A% s0 t/ i
long size;4 [; j) B# T1 O' I1 N8 t
int i = 0;
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for (cnt = (maxsize / sizeof (long)) >> 1; cnt > 0; cnt >>= 1) {' p/ R; q( \( s5 M
addr = base + cnt; /* pointer arith! */
2 P; L- {% e9 x7 W7 e. t0 ?& E sync ();: N2 u4 l0 V7 Q
save[i++] = *addr;+ K. ?! P! y8 @
sync ();
# G: C+ r6 J7 _8 j! y- f- T *addr = ~cnt;
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addr = base;" N+ A# d2 {9 _5 W) t% i
sync ();5 E- g% S* ` Q- t. O% g
save = *addr;
* g& Y, L% p# @: |9 X- b4 | sync ();
* r( o/ ~6 v @$ m% o *addr = 0;
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sync ();* _+ ?: e l" |" ~" v9 b
if ((val = *addr) != 0) {, F% c" o/ i8 I7 i: |' q# `
/* Restore the original data before leaving the function.9 O/ I$ _% G Q
*/: I8 ^( U; j9 E0 u6 {8 G0 H
sync ();
3 e8 n' m- @# H* u! v- g: V *addr = save;1 t7 @; |* s5 @, t4 G
for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) {
/ `) [ }; [) N8 d. f9 g/ o addr = base + cnt;2 Z0 l _* `/ s/ }* K5 Z
sync ();
1 U, ]/ E9 U8 c9 G2 R& ~ *addr = save[--i];1 }2 V h, B( f. T8 v6 U7 F4 `6 w7 O
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return (0);
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for (cnt = 1; cnt < maxsize / sizeof (long); cnt <<= 1) {
- h, W, }. M! [ addr = base + cnt; /* pointer arith! */
8 ^* q8 A( |; Q val = *addr;( O1 k" s5 d0 W
*addr = save[--i];& M8 n P3 L' q% H3 C7 B
if (val != ~cnt) {; Z7 Y7 v8 z4 s( L9 M+ ?
size = cnt * sizeof (long);3 e3 r- l- J* q( I% b$ \9 q
/* Restore the original data before leaving the function.' I$ g9 |$ r/ g3 D5 Z' g; [5 j
*/: @7 G8 o6 x5 R
for (cnt <<= 1; cnt < maxsize / sizeof (long); cnt <<= 1) {' L- `3 I8 ~! o& a% E6 J
addr = base + cnt;
; q! i& I( F1 K/ Q. R/ J" z *addr = save[--i];$ M4 A; o F0 P* A4 G
}
/ i' s8 R! K5 Z5 f" O return (size);
9 {) M8 A3 j6 s/ M) h( p B" S }
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' w/ d; Q& R# b5 J* T p" l return (maxsize);/ t! q! Z1 J: J0 P
}
! b$ u( N# {: H' @5 i8 A. l1 U! jint dram_init(void)
; G' \, f" H5 U& W$ w{
. J/ \3 s: R0 X( w M8 [ /* dram_init must store complete ramsize in gd->ram_size */
/ f) P0 u4 N" i* G3 s+ N8 l; \% l. u* o gd->ram_size = get_ram_size(
! ?1 d6 S" ~: t, @8 j$ k+ @* x (void *)CONFIG_SYS_SDRAM_BASE,
9 k u& _! }. _7 D. T CONFIG_MAX_RAM_BANK_SIZE);! ^% c% E1 V& W) n6 ~0 w( x; B
return 0;0 l0 f: C/ s" T, c' s" N; }
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8 Z- l* U- U: h5 h# MFLASH是通过检查FLASH内部的ID识别容量，希望对您有帮助！) ?/ v6 r7 X4 }2 G3 n2 ~
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发表于 2014-9-11 18:55:41