From: Bert van Hall <bert.vanhall@avionic-design.de>
Date: Tue, 22 Jul 2014 08:33:50 +0000 (+0200)
Subject: Fix XMEGA USB prescaler calculation
X-Git-Tag: LUFA-140928~28^2
X-Git-Url: http://git.linex4red.de/pub/lufa.git/commitdiff_plain/c499a0b7550ba26e4b26e11ae13935f094f22ddc?hp=--cc

Fix XMEGA USB prescaler calculation

The USB prescaler calculation for the CLK.USBCTRL register is changed to
give valid results and set the prescaler correctly.

Signed-off-by: Bert van Hall <bert.vanhall@avionic-design.de>
---

c499a0b7550ba26e4b26e11ae13935f094f22ddc
diff --git a/LUFA/Drivers/USB/Core/XMEGA/USBController_XMEGA.c b/LUFA/Drivers/USB/Core/XMEGA/USBController_XMEGA.c
index f8b0fc6af..b5de862f1 100644
--- a/LUFA/Drivers/USB/Core/XMEGA/USBController_XMEGA.c
+++ b/LUFA/Drivers/USB/Core/XMEGA/USBController_XMEGA.c
@@ -109,15 +109,25 @@ void USB_Disable(void)
 
 void USB_ResetInterface(void)
 {
+	uint8_t PrescalerNeeded;
+	uint8_t nbit = 0;
+
 	#if defined(USB_DEVICE_OPT_FULLSPEED)
 	if (USB_Options & USB_DEVICE_OPT_LOWSPEED)
-	  CLK.USBCTRL = (((F_USB / 6000000) - 1) << CLK_USBPSDIV_gp);
+	  PrescalerNeeded = F_USB / 6000000;
 	else
-	  CLK.USBCTRL = (((F_USB / 48000000) - 1) << CLK_USBPSDIV_gp);
+	  PrescalerNeeded = F_USB / 48000000;
 	#else
-	CLK.USBCTRL = (((F_USB / 6000000) - 1) << CLK_USBPSDIV_gp);
+	PrescalerNeeded = F_USB / 6000000;
 	#endif
 
+	while (PrescalerNeeded && nbit < 7) {
+		PrescalerNeeded >>= 1;
+		nbit++;
+	}
+
+	CLK.USBCTRL = (nbit - 1) << CLK_USBPSDIV_gp;
+
 	if (USB_Options & USB_OPT_PLLCLKSRC)
 	  CLK.USBCTRL |= (CLK_USBSRC_PLL_gc   | CLK_USBSEN_bm);
 	else