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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:( I3 V, l9 w ~
/*/ E, c& [& j/ P4 K# B, J" ?
* Check memory range for valid RAM. A simple memory test determines1 T# s7 e1 S# ~$ r0 b9 n
* the actually available RAM size between addresses `base' and
|' } c( g) R5 S# y6 V! X* `base + maxsize'.; u$ \# a _( z3 y* h
*/$ @8 [' \, p4 a
long get_ram_size(long *base, long maxsize)2 e4 ^: `6 e [ m# R5 l
{
* N- Y( u3 r$ ?! h. L1 L# E volatile long *addr;5 L, P" j0 q7 X
long save[32];
0 K$ [/ i* U: @( M+ Y& Y+ @ long cnt;0 L d' y! i0 P: v
long val;. O+ p, y5 h+ b2 |$ M
long size;
% ~5 M# L j3 S- g# B int i = 0;$ H5 U1 \6 s2 `+ f
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for (cnt = (maxsize / sizeof (long)) >> 1; cnt > 0; cnt >>= 1) {. I: B, w' V$ c5 M1 h* W
addr = base + cnt; /* pointer arith! */
+ o, |3 N/ E& {. h3 w0 F sync ();
3 j! G' ^3 R; s$ R4 _ save[i++] = *addr; E3 x! {6 C8 x: b9 e0 ?* _
sync ();
( O' W" H2 U" R* ?8 M. ` *addr = ~cnt;
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% V, Z+ A" n" h- c- D addr = base;7 q; h/ o& d# t4 R
sync ();
5 U! G7 p4 b, {& ?4 g+ L save = *addr;" {1 K `9 q+ A/ u5 ]
sync ();! h5 {0 C" h5 z* d! v
*addr = 0;* w8 x9 k% @: T) }/ a1 H! [$ r- Q
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sync ();( r/ N: w# q \3 @
if ((val = *addr) != 0) {# u0 ]2 J& J% g, g3 D3 D
/* Restore the original data before leaving the function.( S* X1 k. z4 k9 p' i6 s6 x
*/
+ v8 g# }; t1 {# a# K& A sync ();
1 i1 Z. N/ K6 t- v! c: D *addr = save;
5 D" n% q; @3 m$ _ for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) {
2 z/ s3 S9 a7 {+ O addr = base + cnt;
9 N' L: p h$ o6 x& d( n4 X% H- [3 t sync ();
$ H/ c6 A* Y* u/ f8 U( X# P *addr = save[--i];
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return (0);
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for (cnt = 1; cnt < maxsize / sizeof (long); cnt <<= 1) {
* a( h; g$ E! E6 F addr = base + cnt; /* pointer arith! */* f0 e7 p1 X4 k0 s5 Z. u: T$ s: b
val = *addr;8 ?! n \% k5 k' ?) B
*addr = save[--i];
* a$ L' h! i( V$ E1 C) N if (val != ~cnt) {& H* P( J: t* u$ x
size = cnt * sizeof (long);
( L) J& p, l: M! h( }+ F( n4 Y /* Restore the original data before leaving the function.
) ^1 u2 ^; D- i. d- `9 ?4 [ */
. m3 ~1 p* r/ M7 L for (cnt <<= 1; cnt < maxsize / sizeof (long); cnt <<= 1) { v6 j7 T% ~+ J) k- u1 ~6 O
addr = base + cnt;
1 Q1 h7 L4 \; F- G *addr = save[--i];7 M* I& u C% Z, m$ T; i+ W
}
( f1 v* W% m/ y2 M return (size);) Z4 G! n" ?- u; L
}
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# a6 z3 w/ t- `1 V
O( { q9 ?0 S" L+ B3 Y return (maxsize);
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int dram_init(void)& H( ?1 m6 y* Y- A
{
- {4 w2 J: v# G( z/ } /* dram_init must store complete ramsize in gd->ram_size */' L$ v" `3 `; e. ]% |
gd->ram_size = get_ram_size(
5 N e8 e# Y, N$ ~$ P (void *)CONFIG_SYS_SDRAM_BASE,
( D7 \& C: k0 H( h8 {* V. j; z. F CONFIG_MAX_RAM_BANK_SIZE);* j9 l( _* f' [+ }; }; @( x/ D
return 0;5 W$ b" f! w6 v/ T8 G
}
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! M. C# I- n t3 k) V FFLASH是通过检查FLASH内部的ID识别容量,希望对您有帮助!' w) `9 w4 _4 E# f0 p
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