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/* error correcting code for nand flash */
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#include "u.h"
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#include "../port/lib.h"
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#include "mem.h"
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#include "dat.h"
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#include "fns.h"
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#include "io.h"
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#include "../port/error.h"
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#include "nandecc.h"
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#define CORRECTABLEMASK 0x545555
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static uchar ecctab[] = {
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0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
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0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
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0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
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0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
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0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
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0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
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0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
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0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
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0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
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0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
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0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
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0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
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0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
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0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
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0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
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0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
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0xa9, 0xfc, 0xf0, 0xa5, 0xcc, 0x99, 0x95, 0xc0,
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0xc0, 0x95, 0x99, 0xcc, 0xa5, 0xf0, 0xfc, 0xa9,
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0x3c, 0x69, 0x65, 0x30, 0x59, 0x0c, 0x00, 0x55,
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0x55, 0x00, 0x0c, 0x59, 0x30, 0x65, 0x69, 0x3c,
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0x30, 0x65, 0x69, 0x3c, 0x55, 0x00, 0x0c, 0x59,
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0x59, 0x0c, 0x00, 0x55, 0x3c, 0x69, 0x65, 0x30,
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0xa5, 0xf0, 0xfc, 0xa9, 0xc0, 0x95, 0x99, 0xcc,
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0xcc, 0x99, 0x95, 0xc0, 0xa9, 0xfc, 0xf0, 0xa5,
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0x0c, 0x59, 0x55, 0x00, 0x69, 0x3c, 0x30, 0x65,
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0x65, 0x30, 0x3c, 0x69, 0x00, 0x55, 0x59, 0x0c,
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0x99, 0xcc, 0xc0, 0x95, 0xfc, 0xa9, 0xa5, 0xf0,
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0xf0, 0xa5, 0xa9, 0xfc, 0x95, 0xc0, 0xcc, 0x99,
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0x95, 0xc0, 0xcc, 0x99, 0xf0, 0xa5, 0xa9, 0xfc,
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0xfc, 0xa9, 0xa5, 0xf0, 0x99, 0xcc, 0xc0, 0x95,
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0x00, 0x55, 0x59, 0x0c, 0x65, 0x30, 0x3c, 0x69,
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0x69, 0x3c, 0x30, 0x65, 0x0c, 0x59, 0x55, 0x00,
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};
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ulong
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nandecc(uchar *buf)
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{
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int cp, zeros, ones, im, lp, om, i;
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cp = 0xff;
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zeros = 0xff;
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ones = 0xff;
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for (i = 0; i < 256; i++) {
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int tabent = ecctab[buf[i]];
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cp ^= tabent;
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if (tabent & 1) {
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zeros ^= ~i;
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ones ^= i;
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}
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}
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lp = 0;
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for (im = 0x80, om = 0x8000; im; im >>= 1, om >>= 1) {
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if (ones & im)
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lp |= om;
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om >>= 1;
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if (zeros & im)
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lp |= om;
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}
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return (((cp & 0xff) | 3) << 16) | lp;
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}
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NandEccError
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nandecccorrect(uchar *buf, ulong calcecc, ulong *storedecc, int reportbad)
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{
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ulong xorecc, mask;
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int k;
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if (calcecc == *storedecc)
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return NandEccErrorGood;
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if (reportbad)
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print("nandecccorrect: calculated ecc %.8lux stored ecc %.8lux\n",
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calcecc, *storedecc);
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xorecc = calcecc ^ *storedecc;
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if (((xorecc ^ (xorecc >> 1)) & CORRECTABLEMASK) == CORRECTABLEMASK) {
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ulong imask;
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ushort out, omask;
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int line, col;
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for (imask = 0x800000, omask = 0x800, out = 0; imask;
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imask >>= 2, omask >>= 1)
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if (xorecc & imask)
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out |= omask;
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line = out & 0xff;
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col = out >> 9;
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if (reportbad)
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print("nandecccorrect: single bit error line %d col %d\n",
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line, col);
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buf[line] ^= (1 << col);
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*storedecc = calcecc;
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return NandEccErrorOneBit;
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}
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for (mask = 0x800000, k = 0; mask; mask >>= 1)
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if (mask & xorecc)
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k++;
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if (k == 1) {
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if (reportbad)
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print("nandecccorrect: single bit error in ecc\n");
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/* assume the stored ecc was wrong */
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*storedecc = calcecc;
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return NandEccErrorOneBitInEcc;
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}
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if (reportbad)
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print("nandecccorrect: 2 bit error\n");
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return NandEccErrorBad;
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}
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