Fix a few issues with EDID established timings

Detail:
  c/ScrModes:
  - Added established timings for 720x400 @ 70Hz to be used in place of the auto-generated timings. For a BenQ FP737s-D, these match the expected timings listed in the manual, and they actually result in a picture displaying (auto-generated timings did not).
  - Split the guts of generate_dmt_mode out into a separate function so it can easily be used for adding the 720x400 @ 70Hz ModeDefinition
  - Fix established timing handling to only call generate_dmt_mode if the DMT defines timings for a given mode (old logic meant that only 720x400 @ 70Hz was falling through to the auto-generate case)
  - Fix established timing auto-generation to cope with the possibility of timings_byte being non-zero
Admin:
  Tested on iMx6 on a variety of monitors
  720x400 @ 70Hz now displays correctly on a FP737s-D
  640x480 @ 67Hz now works too (albeit with a warning about being a non-preset mode, this one is listed in the EDID but not in the manual)


Version 0.50. Tagged as 'ScrModes-0_50'

VersionNum

-/* (0.49)
+/* (0.50)
  *
  * This file is automatically maintained by srccommit, do not edit manually.
  * Last processed by srccommit version: 1.1.
  *
  */
-#define Module_MajorVersion_CMHG        0.49
+#define Module_MajorVersion_CMHG        0.50
 #define Module_MinorVersion_CMHG        
-#define Module_Date_CMHG                29 Nov 2015
+#define Module_Date_CMHG                15 Dec 2015
 
-#define Module_MajorVersion             "0.49"
-#define Module_Version                  49
+#define Module_MajorVersion             "0.50"
+#define Module_Version                  50
 #define Module_MinorVersion             ""
-#define Module_Date                     "29 Nov 2015"
+#define Module_Date                     "15 Dec 2015"
 
-#define Module_ApplicationDate          "29-Nov-15"
+#define Module_ApplicationDate          "15-Dec-15"
 
 #define Module_ComponentName            "ScrModes"
 #define Module_ComponentPath            "castle/RiscOS/Sources/Video/UserI/ScrModes"
 
-#define Module_FullVersion              "0.49"
-#define Module_HelpVersion              "0.49 (29 Nov 2015)"
-#define Module_LibraryVersionInfo       "0:49"
+#define Module_FullVersion              "0.50"
+#define Module_HelpVersion              "0.50 (15 Dec 2015)"
+#define Module_LibraryVersionInfo       "0:50"

c/ScrModes

@@ -456,6 +456,23 @@ static const char established_timings3[] = {
     /* N.B. 7th byte not checked */
 };
 
+/*
+ * Established timings for 720x400 @ 70Hz
+ * Derived from:
+ *
+ * http://www.javiervalcarce.eu/html/vga-signal-format-timming-specs-en.html
+ * http://www.epanorama.net/documents/pc/vga_timing.html
+ *
+ */
+
+static const ModeDefinition established_timing_7 =
+{
+    /* 720 x 400 @ 70Hz */
+    "720 x 400",    720,  400, 108,  54, 0,  720, 0, 18,
+                                 2,  34, 0,  400, 0, 13,
+                   28322, -1,   NP,   0, 70, 0
+};
+
 /* List of standard timings - ie modes who have a defined 2-byte code in the DMT document.
  *
  * NB The third parameter is DMT NUMBER, not ARRAY NUMBER. This is usually
@@ -1636,6 +1653,32 @@ static int add_proposed_mode(MonitorDescriptionRef monitor_definition, ModeDescr
 }
 
 
+/* Copy a builtin mode and add it to the monitor description
+ */
+static _kernel_oserror *add_builtin_mode(MonitorDescriptionRef monitor, const ModeDefinition *mode, uint8_t priority)
+{
+    ModeDescriptionRef mode_desc = (ModeDescriptionRef) malloc (sizeof(ModeDescription));
+    if (mode_desc == NULL) {
+        return error (ERR_NOSPACE, 0, 0, 0);
+    }
+
+    mode_desc->definition = *mode;
+    compute_modedescription(mode_desc);
+    mode_desc->frame_hz = mode->freq;
+    mode_desc->priority = priority;
+
+    if (add_proposed_mode(monitor, mode_desc) == 0) {
+      free(mode_desc);
+      return NULL;
+    }
+
+#if DODEBUG
+    display_mode_parameters(mode_desc);
+#endif
+
+    return NULL;
+}
+
 /* generate_dmt_mode creates a mode using standardised timing parameters.
  * These come from the Display Monitor Timing Document (VESA).
  * They are part of EDID 1.0 to 1.3 and should be used where a DMT
@@ -1649,24 +1692,12 @@ static _kernel_oserror *generate_dmt_mode(char dmt, MonitorDescriptionRef monito
     if (dmt > 0)
     {
         dmt--; /* Convert DMT back to array number */
-        ModeDescriptionRef mode_desc = (ModeDescriptionRef) malloc (sizeof(ModeDescription));
-        if (mode_desc == NULL) {
-            return error (ERR_NOSPACE, 0, 0, 0);
-        }
-
-        mode_desc->definition = display_monitor_timings[dmt];
-        compute_modedescription(mode_desc);
-        mode_desc->frame_hz = display_monitor_timings[dmt].freq;
-        mode_desc->priority = priority;
-
-        if (add_proposed_mode(monitor, mode_desc) == 0) {
-          free(mode_desc);
-        }
 
         #if DODEBUG
         printf("Established Modes Display Monitor Timing :\n");
-        display_mode_parameters(mode_desc);
         #endif
+
+        return add_builtin_mode(monitor, &display_monitor_timings[dmt], priority);
     }
 #if DODEBUG
     else
@@ -3121,9 +3152,12 @@ static _kernel_oserror *parseedid(char *ediddata, const char *file)
         {
             if ((edidblockref->established_timings[timings_byte] & (1<<(timings_bit%8))) == (1<<(timings_bit%8)))
             {
-              int dmt_mode = (timings_byte * 8)+(7 - timings_bit);
+#if DODEBUG
+              printf("Timings bitfield byte %d bit %d:\n", timings_byte, timings_bit);
+#endif
+              int dmt_mode = established_timings[(timings_byte * 8)+(7 - timings_bit)];
               if (dmt_mode > 0) {
-                  generate_dmt_mode(established_timings[dmt_mode], new_monitor, 6);
+                  generate_dmt_mode(dmt_mode, new_monitor, 6);
               }
               else {
                   // There are 3 cases who do not have defined DMT codes.
@@ -3131,12 +3165,11 @@ static _kernel_oserror *parseedid(char *ediddata, const char *file)
                   int xres = 0;
                   int yres = 0;
                   int freq = 0;
-                  switch (timings_bit)
+                  switch (timings_bit | (timings_byte << 3))
                   {
-                    case 7: // 720 X 400 @ 40Hz
-                      xres = 720;
-                      yres = 400;
-                      freq = 70;
+                    case 7: // 720 X 400 @ 70Hz
+                      /* Use some fixed timings for better compatibility */
+                      add_builtin_mode(new_monitor, &established_timing_7, 6);
                       break;
                     case 6: // 720 X 400 @ 88Hz
                       xres = 720;