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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:' r, `" T2 @7 n% A
/*7 I2 B. |' C3 p. W6 S
* Check memory range for valid RAM. A simple memory test determines
?. ^1 Z4 W8 U; J5 ~# W; w* the actually available RAM size between addresses `base' and4 P8 q' F4 g5 v
* `base + maxsize'.6 j. H2 F8 V& b1 ^% Q, E# ~9 J3 B
*/
& k/ V8 _% A8 I' f7 a6 Tlong get_ram_size(long *base, long maxsize): p4 P- Y6 L/ j3 G
{
3 k+ w; C* C8 S) g) \& g* N; Q volatile long *addr;
) ~( I( Q! z9 I, C# u long save[32];
. k B7 `: L s0 l1 C long cnt;
3 g* d2 J9 w. Y( y0 [+ O; D long val;
7 Y8 C% p8 y) \9 H3 T: M3 l2 ]' R long size;& t o: `' l4 U- h
int i = 0;
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for (cnt = (maxsize / sizeof (long)) >> 1; cnt > 0; cnt >>= 1) {
! _" |, K) x! v) B$ J% H addr = base + cnt; /* pointer arith! */
# \! i! W8 P2 U0 u4 \0 k6 `+ ` sync ();9 J! N0 ^' ]5 R' p% u
save[i++] = *addr;% ~7 F B) }' q1 D$ m; c# }: C
sync ();; g+ z* X7 n n$ _: n/ l
*addr = ~cnt;
! _% e6 Q5 @' R' \7 v }
* V' T1 q C# D7 B* i6 {
/ ~- a6 A6 C ?* H. `3 x addr = base;
; E/ X: q6 Q8 }3 t: u6 N6 S6 b! b sync ();( i2 M" C! ~# B4 B* H3 x3 X( m- ~
save = *addr;* [2 R5 {- C: W9 P+ h
sync ();
5 z, Y% u+ i) T' ~7 k c) T *addr = 0;% l8 X' M) a& Q) ~& v7 I& d8 S
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sync ();
% ?7 S J5 }# k8 z& b+ h if ((val = *addr) != 0) {0 L6 A# k @, [. x
/* Restore the original data before leaving the function.
- L1 \$ ~! W' j. n0 r */4 W9 v) ~6 @( z. t' p
sync ();, E. R3 z$ n, P/ m4 R; k/ s3 |
*addr = save;% W2 H, y' R( `3 F: z# Q' Q6 G
for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) {9 `# O( n4 O3 S- P* _
addr = base + cnt;
: j6 g& d0 x* e* `9 i1 v8 ` sync ();1 R" q8 E( o* Q" }! Y
*addr = save[--i];$ Y' G1 J! W% o( K b. Y# ]
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return (0);; c8 m" r# D7 x5 [8 |* ~
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) m4 Z4 X, y) B2 Z) }
for (cnt = 1; cnt < maxsize / sizeof (long); cnt <<= 1) {6 x& k0 P, O( B; w: W, i% D* ^5 F
addr = base + cnt; /* pointer arith! */2 V1 w( G5 K3 d, C
val = *addr;
+ c, h7 I4 u5 y" u *addr = save[--i];* w, N' C& Z# q% e, y) b' l
if (val != ~cnt) {
: J5 K1 D5 \, s' k size = cnt * sizeof (long);9 N2 ?+ A2 g7 Q R4 @* ^5 e0 W
/* Restore the original data before leaving the function.# G! Y$ }! p$ c
*/5 ~' I# r2 F1 f0 k/ g; V! h
for (cnt <<= 1; cnt < maxsize / sizeof (long); cnt <<= 1) {
8 x* M# R& z# R addr = base + cnt;2 O( Y2 Q7 l! e! ]( O
*addr = save[--i];
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return (size);
0 G; J% r4 D3 w1 w }
2 Q5 j. K. ]$ F5 o2 F }
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% U0 H% [) t# w2 k3 M return (maxsize);
, i9 h* d4 P+ j; H7 `; `. x}
" _, ]8 k u& ]& ?9 h7 ^6 ~& xint dram_init(void)
/ t/ y+ S# Z" X* C) K; W{
1 M! O x+ ~' |0 N: Q- Q9 \ /* dram_init must store complete ramsize in gd->ram_size */
( }8 ]: ~# e0 y* E6 ]# y8 U- | gd->ram_size = get_ram_size(
" ^0 W" H6 k |2 s8 T (void *)CONFIG_SYS_SDRAM_BASE,
& |: E$ u" L! D9 L* W) T6 i CONFIG_MAX_RAM_BANK_SIZE);6 l, M# H1 U) A: G' e& A
return 0;
+ c2 u! X4 `1 k% B, M% R}
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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!7 V' u; E/ d' r% H* J) z% x$ i3 a
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