Change I2C speed depending on the kind of write

- Long writes are slow to prevent errors mid-sequence (flickering)
  * This is likely to have something to do with the PWM registers
- Short writes are fast to prevent noise during page setup
- Leaving zero pages and send page as short writes (seem to error just
  like the short register writes)

Author: haata

Scan/Devices/ISSILed/i2c.c

@@ -650,7 +650,6 @@ void i2c_isr( uint8_t ch )
 #if defined(_kinetis_)
 				*I2C_D = element;
 #elif defined(_sam_)
-				// while (! (status & TWI_SR_TXRDY));
 				if (!(status & TWI_SR_TXRDY)) return;
 				twi_dev->TWI_THR = element;
 #endif

Scan/Devices/ISSILed/led_scan.c

@@ -666,9 +666,6 @@ void LED_reset()
 		GPIO_Ctrl( hardware_shutdown_pin, GPIO_Type_DriveHigh, GPIO_Config_Pullup );
 	}
 
-	// Initialize I2C in slow mode
-	i2c_setup(0);
-
 	// Force PixelMap to be ready for the next frame
 	Pixel_FrameState = FrameState_Update;
 
@@ -818,12 +815,18 @@ inline void LED_setup()
 uint8_t LED_chipSend;
 void LED_linkedSend()
 {
+	// Initialize I2C in slow mode
+	i2c_setup(0);
+
 	// Check if we've updated all the ISSI chips for this frame
 	if ( LED_chipSend >= ISSI_Chips_define )
 	{
 		// Now ready to update the frame buffer
 		Pixel_FrameState = FrameState_Update;
 
+		// Initialize I2C in fast mode
+		i2c_setup(1);
+
 		// Finished sending the buffer, exit linked send
 		return;
 	}