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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:
+ R4 }- `" }+ [- v5 A/*
; M% O1 p' j0 o( b0 t4 ]1 U/ M" d0 m* X* Check memory range for valid RAM. A simple memory test determines
' r* q3 n4 o3 l, V* the actually available RAM size between addresses `base' and
. d" B4 k8 a0 z$ R* `base + maxsize'.: v9 B% D f& } p. @
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long get_ram_size(long *base, long maxsize)& H% i& Z9 A T R
{
+ Z. b. `$ s1 b1 O0 t; _$ T volatile long *addr;+ n. |" S0 U+ ]0 H
long save[32];3 D z! E" G j$ c
long cnt;
/ V8 n/ d, Y6 r5 @$ B long val;
5 d" g" S. b' V) v long size;0 [ K7 l$ U4 d' H+ p! B
int i = 0;
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. O o9 [# H0 }7 K for (cnt = (maxsize / sizeof (long)) >> 1; cnt > 0; cnt >>= 1) {9 [8 f d' t$ v V% c5 t7 t: p
addr = base + cnt; /* pointer arith! */
* j, u6 `+ _0 b: {7 Z* @9 g sync ();; }/ @9 S+ ^& A4 {- f% s9 u
save[i++] = *addr;
, {( H( K2 Z8 W9 U& @) X sync ();
- L6 J8 p; |) e# |$ j" z& g *addr = ~cnt;( A3 O8 F$ b! a
}
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9 ]: D/ n. N- D! B5 q0 P2 h addr = base;7 e8 A$ J \; @" e! w* ~ c
sync ();
1 V8 J7 B* u; Z9 K save = *addr;
! R- h4 U8 e( O: W sync ();
5 M- Y8 _9 m2 c+ G. K+ E *addr = 0;
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) k0 u* E* c2 I" Q/ _ sync ();' |5 _+ G8 X& W
if ((val = *addr) != 0) {* Z5 S5 y9 m0 D8 K
/* Restore the original data before leaving the function.
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sync ();: m' t& \& d; D% r$ j
*addr = save; y! P* ]/ y7 e2 N& ~6 x
for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) {
! G; d( q% d$ I8 _- b- V addr = base + cnt;
/ {. V3 K2 q) a, s sync ();. Q3 N- _ V- ~" h3 K( w
*addr = save[--i];6 p0 y: T, R3 W4 \* @4 n4 j f
}
/ w( J! s6 x$ O8 E$ B( }& H return (0);2 ?) _5 K$ u) B: M
}
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8 y1 l) J0 X' I% v# y, t a for (cnt = 1; cnt < maxsize / sizeof (long); cnt <<= 1) {- t2 H. J9 N4 ~1 Y
addr = base + cnt; /* pointer arith! */9 }8 O" B+ |) ~* _; M! Q
val = *addr;. \* N$ B& p( C0 W6 X
*addr = save[--i];
: R+ z% a5 {# t8 k& ~; S, Z6 } if (val != ~cnt) {; h" w8 r( h- Y% U- g& _4 Z
size = cnt * sizeof (long);' Q# U; M+ K' a+ I& h5 @
/* Restore the original data before leaving the function.
( p# y/ I4 _ ] */
. I$ K4 }! |4 g% F" z for (cnt <<= 1; cnt < maxsize / sizeof (long); cnt <<= 1) {6 o; @$ O9 B* |
addr = base + cnt;
) A, H) U& S$ y8 t/ E: r$ [1 a *addr = save[--i];
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return (size);
; C; ?1 M t2 J# e% A }
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, \; S" l* ^/ B! e# a' q return (maxsize);8 l& a$ Y6 ~6 L6 t: H7 A! b
}
' a3 {! @1 ?! k- _# U/ k# aint dram_init(void)7 L; K2 P6 M, C
{
. ?% J$ B6 a E /* dram_init must store complete ramsize in gd->ram_size */
7 Q9 g% x6 }; e6 [6 d7 V gd->ram_size = get_ram_size(
3 s( v G" K4 _6 G4 c+ R' a1 o: | (void *)CONFIG_SYS_SDRAM_BASE,2 w9 |; d* z1 X2 T$ ~ \' z
CONFIG_MAX_RAM_BANK_SIZE);
+ G0 q/ E' F: T" | b. ~ return 0;) [+ |: G3 T3 H' p; @
}" E0 y3 O, c! \& K8 o- }
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`" B% M* b1 L! u; U- |. zFLASH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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