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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
- ^' H& ]8 Z9 l* the actually available RAM size between addresses `base' and. n' N& o& {- @5 F
* `base + maxsize'.
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long get_ram_size(long *base, long maxsize)
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volatile long *addr;
, `; y5 ?$ U3 J0 M& o5 K3 } long save[32];' y1 z# N, Z% U2 ]1 i3 b
long cnt;6 i7 n, p/ x J& i9 @# G( Q- t1 k
long val;* f H" s! r' r$ [/ L8 i1 p
long size;
, g5 R9 F6 ]" y& s5 ^ int i = 0;
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for (cnt = (maxsize / sizeof (long)) >> 1; cnt > 0; cnt >>= 1) {
9 v f: d( e! P: @ addr = base + cnt; /* pointer arith! */2 d: Z7 M% s& k) Z: \) i! R
sync ();
" Q4 g( S4 L. t1 d save[i++] = *addr;8 s, O: v" m! M
sync ();
2 h5 {+ A0 Q3 ?$ r) G. F8 m: h *addr = ~cnt;, g o" n4 `+ s
}
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addr = base;* T7 y0 c7 W7 W* U; O$ g9 s
sync ();4 B1 E$ s3 n5 k& C- E
save = *addr;
8 `7 L/ O7 }* P U sync ();# M7 c' S# T/ P7 N* h6 p$ I
*addr = 0;
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sync ();2 N# W9 V- D3 [. S! J8 E. _- [
if ((val = *addr) != 0) {3 b# r" l* E, ]/ N9 H
/* Restore the original data before leaving the function.- h2 n/ f* J1 h1 O! f( j g+ @
*/) C9 h) l/ u. P' D. ]
sync ();5 a0 T1 c2 J) y+ t
*addr = save;
/ Z7 x' A' _6 }3 [" F9 z4 X for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) {
1 h% Y0 Q6 _' ~. J. E% l addr = base + cnt;
0 D% L6 H' n! x& b/ T1 v sync ();
4 H0 H) Q: z+ y; n* {$ Z *addr = save[--i];
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6 V8 Z5 j% Z4 Z% k return (0);
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+ g2 E3 x* w# W) N7 Y( W3 ^ for (cnt = 1; cnt < maxsize / sizeof (long); cnt <<= 1) {. B2 V- r+ O' B" o
addr = base + cnt; /* pointer arith! */$ w; T% A- H4 N. B2 e# G0 v3 O
val = *addr;* |: ]8 Y/ w) R* U
*addr = save[--i];
; I- z! Z! C1 t" g& S if (val != ~cnt) {
5 e; L r3 s9 |* S8 l2 \1 y# ? size = cnt * sizeof (long);" P4 T; o3 n# n% ]
/* Restore the original data before leaving the function.5 D9 \& r/ p% h% Q) r) q
*/
7 _5 D# H( Y& k/ P for (cnt <<= 1; cnt < maxsize / sizeof (long); cnt <<= 1) {0 Z6 f4 J+ c! w: V0 o( Q/ ?
addr = base + cnt;' }0 H, t1 W1 ~4 ?
*addr = save[--i];$ M, x8 p4 \$ m8 o* T- {! O
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return (size);
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return (maxsize);
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4 g! S; ~; I, d# j4 rint dram_init(void)' k7 z/ T; C I& K$ @: B1 @( b; \4 [
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/* dram_init must store complete ramsize in gd->ram_size */, g+ p- x3 M4 j
gd->ram_size = get_ram_size(7 N' R# R$ V( d: v
(void *)CONFIG_SYS_SDRAM_BASE,
1 Q: W+ m! n: d& o8 e. N; F! e+ m# Q CONFIG_MAX_RAM_BANK_SIZE);
$ s* t- `" M% Z return 0;8 i1 I! I2 s8 P
}
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# N) o4 T; B( {3 f( p1 ~ CFLASH是通过检查FLASH内部的ID识别容量,希望对您有帮助!( P4 q! ]1 l v
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