Add a configuration flag to disable dithering

README.md

@@ -101,7 +101,7 @@ Type code | Meaning of 'final' bit          | Index range | Packet contents
 --------- | ------------------------------- | ----------- | -------------------------------------
 0         | Interpolate to new video frame  | 0 … 24      | Up to 21 pixels, 24-bit RGB
 1         | Instantly apply new color LUT   | 0 … 24      | Up to 31 16-bit lookup table entries
-2         |                                 |             | (reserved)
+2         | (reserved)                      | 0           | Set configuration data
 3         |                                 |             | (reserved)
 
 In a type 0 packet, the USB packet contains up to 21 pixels of 24-bit RGB color data. The last packet (index 24) only needs to contain 8 valid pixels. Pixels 9-20 in these packets are ignored.
@@ -134,6 +134,13 @@ Byte Offset   | Description
 62            | LUT entry #30, low byte
 63            | LUT entry #30, high byte
 
+A type 2 packet sets optional device-wide configuration settings. Right now it's just used to disable dithering for debug or side-by-side comparison purposes. Other bytes in this packet are reserved.
+
+Byte Offset   | Description
+------------- | ------------
+0             | Control byte
+1             | Flags. Bit 0: Disable dithering
+
 
 Contact
 -------

firmware/fadecandy.cpp

@@ -419,5 +419,10 @@ extern "C" int main()
 
         updateDrawBuffer((millis() << 4) & 0xFFFF);
         leds.show();
+
+        // Optionally disable dithering by clearing our residual buffer every frame.
+        if (buffers.flags & CFLAG_NO_DITHERING) {
+            memset(residual, 0, sizeof residual);
+        }
     }
 }

firmware/fc_usb.cpp

@@ -32,6 +32,7 @@
 
 #define TYPE_FRAMEBUFFER    0x00
 #define TYPE_LUT            0x40
+#define TYPE_CONFIG         0x80
 
 
 
@@ -70,6 +71,11 @@ void fcBuffers::handleUSB()
                 }
                 break;
 
+            case TYPE_CONFIG:
+                flags = packet->buf[1];
+                usb_free(packet);
+                break;
+
             default:
                 usb_free(packet);
                 break;

firmware/fc_usb.h

@@ -89,6 +89,13 @@ struct fcColorLUT : public fcPacketBuffer<PACKETS_PER_LUT>
 };
 
 
+/*
+ * Configuration flag values
+ */
+
+#define CFLAG_NO_DITHERING      (1 << 0)
+
+
 /*
  * All USB-writable buffers
  */
@@ -104,6 +111,8 @@ struct fcBuffers
     fcColorLUT lutNew;                   // Partial LUT, not yet finalized
     uint16_t lutCurrent[LUT_SIZE + 1];   // Active LUT, linearized for efficiency, padded on the end.
 
+    uint8_t flags;              // Configuration flags
+
     fcBuffers()
     {
         fbPrev = &fb[0];