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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, W8 N& j9 @1 w) S C+ Y0 q/*
1 \4 L' q- C$ w' b* Check memory range for valid RAM. A simple memory test determines: }* n% }% ]) b; b2 I. J
* the actually available RAM size between addresses `base' and( M- O4 P7 { ?
* `base + maxsize'.: T ^( a7 s9 E- M. R h
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long get_ram_size(long *base, long maxsize); A7 U$ q4 O, U/ D- R1 ~% S$ A) r
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volatile long *addr;% r5 ^; ?4 B7 b' w3 i1 c
long save[32];
$ b3 Z- X" X; H5 S! a long cnt;4 y! m6 {0 Q0 T# x, D7 T, d5 S
long val;
7 S, K' G, `! q% E long size;
$ T$ x9 F5 F# R6 W7 D6 G8 _ int i = 0;" l9 |4 U- b9 X2 x) F3 {: u
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for (cnt = (maxsize / sizeof (long)) >> 1; cnt > 0; cnt >>= 1) {2 t5 k" G9 B% o1 t& G
addr = base + cnt; /* pointer arith! */
0 ], F2 i ]& f8 z3 |# f+ Q' } sync ();4 Z! W5 E# c" T1 {( w; f1 w
save[i++] = *addr;
; p* E5 w- y1 E) @7 C2 u, G sync ();
0 h1 z2 e" C0 c7 p% E) k% }) | *addr = ~cnt;7 L6 U- l6 F7 `8 \, l- a
}
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addr = base;
3 F/ T6 F9 f! I' \9 | sync ();
' _9 \6 {. y: f) {+ z4 j save = *addr;
! N. L" T! l" u ?$ I: w- | sync ();
. j8 C9 D" U: J X0 q% ]( o *addr = 0;
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/ M; X6 i- B0 C6 T sync ();0 Q' |: s+ z# n! _: g$ \2 o
if ((val = *addr) != 0) {
* n. E1 }* d( ?4 T /* Restore the original data before leaving the function.
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sync ();
5 P; @# j- m3 U) X& c *addr = save;& }0 ~+ U# a2 }( f
for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) {! ]7 Z: z: [+ }8 F# {
addr = base + cnt;
& V2 B3 D: s5 |3 O0 O/ }9 S sync ();
6 x3 e# M: ^ u/ F6 U *addr = save[--i];
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return (0);# e5 T3 ?5 ? v0 @6 N
}! n$ m, q8 f: V/ _5 q; W
' @0 _5 V7 a; }0 ^7 j- A for (cnt = 1; cnt < maxsize / sizeof (long); cnt <<= 1) {
) v4 ^; {( j3 m6 {1 t: \ addr = base + cnt; /* pointer arith! */
* N- t* M7 H/ Z) Q val = *addr;
4 C5 k& R2 V$ X *addr = save[--i];; K, u( D6 j" }% b8 b& t$ z; l
if (val != ~cnt) {5 V9 V" r) P, {
size = cnt * sizeof (long);
" {3 u4 D6 r! }6 v3 b /* Restore the original data before leaving the function.- N( i+ E2 r% e0 E" s0 [7 l4 o
*/) v# z9 V$ r) G! F7 D# H
for (cnt <<= 1; cnt < maxsize / sizeof (long); cnt <<= 1) {. t4 M5 `% x' Y" g/ F( n
addr = base + cnt;
" c: ~/ o. g; V: w2 c" t( e g0 o *addr = save[--i];! ~4 Y% J: r: R0 ^0 Q) L! B
}3 d. v' l) i$ N3 ?8 b
return (size);
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return (maxsize);' z: \9 F$ I, b/ X( v. G. R
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int dram_init(void)
2 K! t" X/ j' `3 e- Z+ y7 T% p8 N{
4 D& q/ z8 Y9 e /* dram_init must store complete ramsize in gd->ram_size */
, j$ n8 J2 [# w; _/ ^" Q gd->ram_size = get_ram_size(
/ K- J$ Y+ i% G3 Z( |/ k3 U0 O (void *)CONFIG_SYS_SDRAM_BASE,
6 U' S S6 L8 m; d8 ?& H4 t% d/ P CONFIG_MAX_RAM_BANK_SIZE);
8 ^0 ?' M7 W* l, Q return 0;0 ]6 H3 i- F9 W& P: j* U
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: ~; R) m- o! c( H4 a% ?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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