Merge pull request #10 from pweingar/issue_8

Issue #8

src/dev/channel.c

@@ -417,17 +417,18 @@ short chan_flush(short channel) {
     }
 }
 
-//
-// Attempt to set the position of the channel cursor (if supported)
-//
-// Inputs:
-//  channel = the number of the channel
-//  position = the position of the cursor
-//  base = whether the position is absolute or relative to the current position
-//
-// Returns:
-//  0 = success, a negative number is an error.
-//
+/*
+ * Attempt to set the position of the channel cursor (if supported)
+ *
+ * Inputs:
+ *  channel = the number of the channel
+ *  position = the position of the cursor
+ *  base = whether the position is from the beginning of the channel, relative to the current position,
+ *         or relative to the end of the channel
+ *
+ * Returns:
+ *  0 = success, a negative number is an error.
+ */
 short chan_seek(short channel, long position, short base) {
     p_channel chan;
     p_dev_chan cdev;

src/dev/channel.h

@@ -36,8 +36,9 @@
 #define CDEV_STAT_READABLE  0x04    // The channel has data to read (read will not block)
 #define CDEV_STAT_WRITABLE  0x08    // The channel can accept data (write will not block)
 
-#define CDEV_SEEK_ABSOLUTE  0
-#define CDEV_SEEK_RELATIVE  1
+#define CDEV_SEEK_START     0       /* Seek from the start of the file */
+#define CDEV_SEEK_RELATIVE  1       /* Seek from the current position */
+#define CDEV_SEEK_END       2       /* Seek from teh end of the file */
 
 /*
  * Structure defining a channel
@@ -242,7 +243,8 @@ extern short chan_flush(short channel);
  * Inputs:
  *  channel = the number of the channel
  *  position = the position of the cursor
- *  base = whether the position is absolute or relative to the current position
+ *  base = whether the position is from the beginning of the channel, relative to the current position,
+ *         or relative to the end of the channel
  *
  * Returns:
  *  0 = success, a negative number is an error.

src/dev/fsys.c

@@ -653,13 +653,21 @@ short fchan_seek(t_channel * chan, long position, short base) {
 
     file = fchan_to_file(chan);
     if (file) {
-        if (base == CDEV_SEEK_ABSOLUTE) {
+        if (base == CDEV_SEEK_START) {
+			/* Position relative to the start of the file */
             result = f_lseek(file, position);
             return fatfs_to_foenix(result);
+
         } else if (base == CDEV_SEEK_RELATIVE) {
+			/* Position relative to the current position */
             long current = f_tell(file);
             result = f_lseek(file, current + position);
             return fatfs_to_foenix(result);
+
+        } else if (base == CDEV_SEEK_END) {
+			/* Position relative to the end of the file */
+            result = f_lseek(file, f_size(file) + position);
+            return fatfs_to_foenix(result);
         }
     }
 
@@ -1044,7 +1052,7 @@ short fsys_elf_loader(short chan, long destination, long * start) {
 		}
 		progIndex++;
 	}
-	
+
     *start = header.entry;
 	return 0;
 }