Pi Firmware: Make second PSYNC read conditional on the sample width (skip in PSYNC x2 mode)

Change-Id: I12921e7c649281f8925cce3aa7d4e65f2fa627f6

src/defs.h

@@ -70,8 +70,12 @@
 #define BIT_ODD_SAMPLES       0x02000000  // bit 25, if set only use odd samples
 #define BIT_EVEN_SAMPLES      0x04000000  // bit 26, if set only use even samples
 
+#define BIT_PSYNC_DOUBLE_READ 0x08000000  // bit 27, indicates PSYNC needs to be read twice, once to find the edge
+                                          // then a second time to capture stable data. The v3 CPLD delays PSYNC a
+                                          // couple of cycles, so the read that sees the edge will always capture
+                                          // stable data. The second read is skipped in this case.
 
-                                             // bits 27-31 unused
+                                             // bits 28-31 unused
 
 // R0 return value bits
 #define RET_SW1               0x02

src/macros.S

@@ -9,6 +9,15 @@ wait\@:
         tst    r8, #PSYNC_MASK
         bne    wait\@
 
+        // Read a second time to capture stable data
+        // This is executed only if the sample_width is 0 (=3 bits)
+        // It could be done on CPLD version, but this was easier
+        tst    r3, #BIT_PSYNC_DOUBLE_READ
+        ldrne  r8, [r4]
+        eorne  r8, r3
+        tstne  r8, #PSYNC_MASK
+        bne    wait\@
+
         // toggle the polarity to look for the opposite edge next time
         eor    r8, r3
         eor    r3, #PSYNC_MASK
@@ -571,5 +580,3 @@ waithi\@:
         tstge  r5, #1          // 1 = auto repeat rate
         orreq  r0, #\ret       // Indicate the auto repeated press in the result
 .endm
-
-

src/rgb_to_fb.S

@@ -139,6 +139,10 @@ skip_swap:
         addne  r8, r8, #1
         str    r8, param_h_offset
 
+        // If the sample width is 0 (3 bits) do the second PSYNC read
+        // (maintains backwards compatibility with CPLDv1 and CPLDv2)
+        orreq  r3, r3, #BIT_PSYNC_DOUBLE_READ
+
         ldr    r8, param_palette_control
         cmp    r8, #2
         movgt  r8, #2