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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:
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* Check memory range for valid RAM. A simple memory test determines( }: g& M j ~7 V
* the actually available RAM size between addresses `base' and+ W7 E! V9 I/ F3 B
* `base + maxsize'.+ k) e& b6 L. n! |3 r
*/: a3 ]& }% B! h
long get_ram_size(long *base, long maxsize)& n- W) \- R. L+ V5 l! K2 k. P
{
9 c5 o9 N: b5 j+ S [2 \! ~ volatile long *addr;
- i! g( R* E5 p5 | long save[32];
* r( @ s, W: ` long cnt;, Q2 F+ S9 F. F i7 X: E2 v
long val;$ e r( U" X- S! c! m; |& p$ v1 r" ^! D' U
long size;
, U7 G7 z$ V3 }) o' X# j& t# r int i = 0;
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/ e5 k2 J0 [0 j for (cnt = (maxsize / sizeof (long)) >> 1; cnt > 0; cnt >>= 1) { D8 a4 G6 [* ~! T7 w2 Y; i
addr = base + cnt; /* pointer arith! */
+ B$ j' h1 W: d* ]/ Q$ e sync ();
/ H! s/ J0 H/ j1 g% {% V save[i++] = *addr;
. b% x, \& I! u sync ();
0 c7 I% R: G) ]/ K( d% D8 D8 { *addr = ~cnt;
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addr = base;. X2 Z+ d Y1 D: h/ `9 W
sync (); R4 e5 l% {0 r' X9 V
save = *addr;7 d1 k. z- ]& \7 U' V
sync ();0 i1 O b3 P+ X0 e, t
*addr = 0;2 O5 o- i' t. w& U9 E& e' F
9 K3 f) E* O( b- F1 {. k D9 w sync ();
$ V' @% Q9 M" b if ((val = *addr) != 0) {
( v' l9 |7 b7 ~6 A$ {7 \ /* Restore the original data before leaving the function.& e5 A/ j& d4 Y) s* P
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sync ();& `2 m G' t- P- G! N
*addr = save;; Z5 T3 K" V f1 y
for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) {
% B, q0 g( q* S1 T6 d5 v+ R: @/ ~% { addr = base + cnt;5 g' S) n( \; ?
sync ();( g1 @2 C) p. p! K4 E
*addr = save[--i];
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return (0);1 w& S) x: K* w7 ^
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0 @; a, m/ O+ ~. ^ for (cnt = 1; cnt < maxsize / sizeof (long); cnt <<= 1) {
3 \. C% K7 t) Y) A, C addr = base + cnt; /* pointer arith! */
2 G) J% e& o; G* X' [9 r* Z& v u val = *addr;# h, ^+ \! q. R( O* I4 a9 R
*addr = save[--i];: m. l% j4 Y% q; e- \1 }/ n
if (val != ~cnt) {- h5 G# W. c3 E- ^4 s2 C
size = cnt * sizeof (long);
3 k8 L+ q/ }% \3 ]) z /* Restore the original data before leaving the function.
4 }& ?* p5 I* M+ Q */
2 M! z5 M2 j2 w( \ for (cnt <<= 1; cnt < maxsize / sizeof (long); cnt <<= 1) {
A3 r5 \# i7 p2 \6 c' K6 X addr = base + cnt;
# c6 G! O6 Y7 D) ^% g/ s *addr = save[--i];2 ]# d- E& z3 |
}
: I: `1 H) e, w% _ j6 ~ return (size); R1 |% B0 p* k2 |
}
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k$ F: e3 z2 P6 E' H# L" U: _. E) V return (maxsize);
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int dram_init(void)/ f7 a5 r7 ~7 @
{) P9 @" w4 w' \( E: l
/* dram_init must store complete ramsize in gd->ram_size */
4 n; m% Y4 }5 B% P( Y6 H; m gd->ram_size = get_ram_size(1 W! L* g/ d7 t) e3 F# f
(void *)CONFIG_SYS_SDRAM_BASE,) r% V6 ]4 d: B- T
CONFIG_MAX_RAM_BANK_SIZE);' I" R8 B* e- h- a& R( u
return 0;
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0 b6 V! w2 C- z8 ~ ^. }( ?FLASH是通过检查FLASH内部的ID识别容量,希望对您有帮助!
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