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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& ^* ?% r2 V: W# J A/ i" @. r
* the actually available RAM size between addresses `base' and
# H$ y4 X5 e: E* `base + maxsize'., `2 [0 ~- V0 ~6 h, `
*/, ?6 |# U7 N# i8 z" v8 g
long get_ram_size(long *base, long maxsize)
; u! a" I+ R: D; z{
: {% B' A Q8 D7 @8 V; L volatile long *addr;
6 \! U3 ?& B9 V2 n4 ?; w! I long save[32];
1 _ S# E4 r* n! [ long cnt;3 A: L! w: A5 Z6 [: e4 R, _; ?# p1 x% r
long val;# R3 K0 W4 S9 }" K9 v+ x$ e- c) B# L
long size;/ K4 T4 T9 g6 x; |
int i = 0;& s9 K: R: C) W$ k
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for (cnt = (maxsize / sizeof (long)) >> 1; cnt > 0; cnt >>= 1) {; a/ Z0 e5 m5 @
addr = base + cnt; /* pointer arith! */0 u% a. x) [ d! O0 i
sync ();
! K% w! T+ l# n1 q' I. z- G save[i++] = *addr;
0 L c% s" k$ E. A7 _: @6 t sync ();
' _/ A1 H% J+ P6 {. U8 p *addr = ~cnt;5 K9 o1 L- \" ] V8 r
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addr = base;4 l; r" o$ {. Q, `6 P. m5 B7 p
sync ();
A' y, ^' M; k' l! U$ `8 W/ U+ x save = *addr;
F! B5 } B; p sync ();) l- l# y& T% K6 d
*addr = 0;
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- d7 j9 C1 v, [1 f$ @ sync ();. c# ]. |: _) r
if ((val = *addr) != 0) {
$ w; p+ b% t7 o+ ]* w/ N. O5 V /* Restore the original data before leaving the function.8 Z' A$ q/ {2 e1 G& k
*/9 i' y/ F' j4 X/ ]/ }" z; O/ s4 p0 [
sync ();
+ u. K4 Q( ?9 z" T: i0 U *addr = save;
! a: ^9 e$ O2 Z# L for (cnt = 1; cnt < maxsize / sizeof(long); cnt <<= 1) {
' r* {6 Z# j- Q2 O* \" X addr = base + cnt;
, G% |. g( s, o5 E9 f sync ();& _* h2 {$ X, t, D/ J j( e4 f1 f
*addr = save[--i];
: ]; U) x# t" o Y! f3 {7 @' c" z. [ }
) M3 d: S% X# Q6 x. R" b return (0);
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for (cnt = 1; cnt < maxsize / sizeof (long); cnt <<= 1) {
4 r2 D5 ]$ @% D addr = base + cnt; /* pointer arith! */+ Z- Z$ i2 g% K* g; F
val = *addr;
3 s2 n4 _& H% U! V *addr = save[--i];" l3 n8 P& s# ^
if (val != ~cnt) {- h+ m- k* [) S g5 {- P8 G) v# `
size = cnt * sizeof (long);
1 Q# z) C- }6 T8 ?7 ~) C /* Restore the original data before leaving the function.
' J- Y6 L* H$ L" |$ { */
8 u% Y- h% d% n h for (cnt <<= 1; cnt < maxsize / sizeof (long); cnt <<= 1) {1 ^8 x6 j2 ?7 @& Y: O8 V
addr = base + cnt;6 H, R. V1 O) z# k- P& Q. @' F9 l
*addr = save[--i];
6 L* _& f$ c5 }/ V }
+ [$ f# O. n( ]/ B* p5 ?; F return (size);
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}
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2 D0 R2 i# l" g3 F/ X: p return (maxsize);$ m7 U9 h! ]+ a! U5 v5 E, C* o
}
8 L) I/ h+ A G1 L) c1 e% d/ pint dram_init(void)1 o& Z; C, W9 t8 w7 H% q
{
4 ]2 {& n8 m+ Y3 U9 A: V: D /* dram_init must store complete ramsize in gd->ram_size */
' ^2 a5 r I, R9 ~+ W gd->ram_size = get_ram_size(% _$ y+ x! @* R' m& m5 q
(void *)CONFIG_SYS_SDRAM_BASE,. A5 \3 g; Z" E, r, {
CONFIG_MAX_RAM_BANK_SIZE);4 I+ l" l! I- Z, ]* L& M1 `1 j ^
return 0;: H% T8 B2 N- o. ^0 H5 i
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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!
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