1 /* error correcting code for nand flash */
2 #include "u.h"
3 #include "../port/lib.h"
4 #include "mem.h"
5 #include "dat.h"
6 #include "fns.h"
7 #include "io.h"
8 #include "../port/error.h"
9 #include "nandecc.h"
10
11 #define CORRECTABLEMASK 0x545555
12
13 static uchar ecctab[] = {
14 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
15 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
16 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
17 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
18 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
19 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
20 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
21 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
22 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
23 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
24 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
25 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
26 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
27 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
28 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
29 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
30 0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
31 0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
32 0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
33 0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
34 0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
35 0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
36 0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
37 0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
38 0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
39 0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
40 0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
41 0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
42 0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
43 0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
44 0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
45 0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
46 };
47
48 ulong
nandecc(uchar * buf)49 nandecc(uchar *buf)
50 {
51 int cp, zeros, ones, im, lp, om, i;
52
53 cp = 0xff;
54 zeros = 0xff;
55 ones = 0xff;
56 for (i = 0; i < 256; i++) {
57 int tabent = ecctab[buf[i]];
58
59 cp ^= tabent;
60 if (tabent & 1) {
61 zeros ^= ~i;
62 ones ^= i;
63 }
64 }
65 lp = 0;
66 for (im = 0x80, om = 0x8000; im; im >>= 1, om >>= 1) {
67 if (ones & im)
68 lp |= om;
69 om >>= 1;
70 if (zeros & im)
71 lp |= om;
72 }
73 return (((cp & 0xff) | 3) << 16) | lp;
74 }
75
76 NandEccError
nandecccorrect(uchar * buf,ulong calcecc,ulong * storedecc,int reportbad)77 nandecccorrect(uchar *buf, ulong calcecc, ulong *storedecc, int reportbad)
78 {
79 ulong xorecc, mask;
80 int k;
81
82 if (calcecc == *storedecc)
83 return NandEccErrorGood;
84 if (reportbad)
85 print("nandecccorrect: calculated ecc %.8lux stored ecc %.8lux\n",
86 calcecc, *storedecc);
87 xorecc = calcecc ^ *storedecc;
88 if (((xorecc ^ (xorecc >> 1)) & CORRECTABLEMASK) == CORRECTABLEMASK) {
89 ulong imask;
90 ushort out, omask;
91 int line, col;
92
93 for (imask = 0x800000, omask = 0x800, out = 0; imask;
94 imask >>= 2, omask >>= 1)
95 if (xorecc & imask)
96 out |= omask;
97 line = out & 0xff;
98 col = out >> 9;
99 if (reportbad)
100 print("nandecccorrect: single bit error line %d col %d\n",
101 line, col);
102 buf[line] ^= (1 << col);
103 *storedecc = calcecc;
104 return NandEccErrorOneBit;
105 }
106 for (mask = 0x800000, k = 0; mask; mask >>= 1)
107 if (mask & xorecc)
108 k++;
109 if (k == 1) {
110 if (reportbad)
111 print("nandecccorrect: single bit error in ecc\n");
112 /* assume the stored ecc was wrong */
113 *storedecc = calcecc;
114 return NandEccErrorOneBitInEcc;
115 }
116 if (reportbad)
117 print("nandecccorrect: 2 bit error\n");
118 return NandEccErrorBad;
119 }
120