20060303a

1 files changed, 81 insertions, 0 deletions

diff --git a/libnandfs/correctauxilliary.c b/libnandfs/correctauxilliary.c
new file mode 100644
index 00000000..510aeac4
--- /dev/null
+++ b/libnandfs/correctauxilliary.c
@@ -0,0 +1,81 @@
+#include "lib9.h"
+#include "logfs.h"
+#include "nandfs.h"
+#include "local.h"
+
+static int
+hammingdistance(uchar a, uchar b)
+{
+	uchar c;
+	int i, k;
+	if (a == b)
+		return 0;
+	c =  a ^ b;
+	for (i = 0x80, k = 0; i; i >>= 1)
+		if (c & i)
+			k++;
+	return k;
+}
+
+static int
+allones(uchar *data, int len)
+{
+	while (len-- > 0)
+		if (*data++ != 0xff)
+			return 0;
+	return 1;
+}
+
+LogfsLowLevelReadResult
+_nandfscorrectauxiliary(NandfsAuxiliary *hdr)
+{
+	/*
+	 * correct single bit errors, detect more than 1, in
+	 * tag, signature
+	 * TODO: add nerase and path protection
+	 */
+	LogfsLowLevelReadResult e;
+	int x;
+	int min, minx;
+
+	e = LogfsLowLevelReadResultOk;
+	
+	min = 8;
+	minx = 0;
+	for (x = 0; x < _nandfsvalidtagscount; x++) {
+		int d = hammingdistance(hdr->tag, _nandfsvalidtags[x]);
+		if (d < min) {
+			min = d;
+			minx = x;
+			if (d == 0)
+				break;
+		}
+	}
+	if (min == 1) {
+		hdr->tag = _nandfsvalidtags[minx];
+		e = LogfsLowLevelReadResultSoftError;
+	}
+	else if (min > 1)
+		e = LogfsLowLevelReadResultHardError;
+	else {
+		if (hdr->tag != LogfsTnone) {
+			ulong tmp = getbig4(hdr->parth);
+			if (tmp != 0xfffffffff && _nandfshamming31_26correct(&tmp)) {
+				putbig4(hdr->parth, tmp);
+				if (e != LogfsLowLevelReadResultOk)	
+					e = LogfsLowLevelReadResultSoftError;
+			}
+			tmp = (getbig2(hdr->nerasemagicmsw) << 16) | getbig2(hdr->nerasemagiclsw);
+			if (tmp != 0xffffffff && _nandfshamming31_26correct(&tmp)) {
+				putbig2(hdr->nerasemagicmsw, tmp >> 16);
+				putbig2(hdr->nerasemagiclsw, tmp);
+				if (e != LogfsLowLevelReadResultOk)	
+					e = LogfsLowLevelReadResultSoftError;
+			}
+		}
+		else if (allones((uchar *)hdr, sizeof(*hdr)))
+			e = LogfsLowLevelReadResultAllOnes;
+	}
+			
+	return e;
+}