Circle 7a81e1b4: USB audio accepts an asynchronous feedback value only between 7/8 and 3/2 of the nominal rate, as Linux snd-usb-audio does, and keeps the nominal rate otherwise. Without it a device whose first feedback reads 0 stops Circle on the m_nChunkSizeBytes assertion.

diff --git a/include/circle/usb/usbaudiostreaming.h b/include/circle/usb/usbaudiostreaming.h
index d4c7131..30d6e85 100644
--- a/include/circle/usb/usbaudiostreaming.h
+++ b/include/circle/usb/usbaudiostreaming.h
@@ -161,6 +161,7 @@ private:
 	volatile boolean m_bSyncEPActive;
 	DMA_BUFFER (u32, m_SyncEPBuffer, 1);
 	unsigned m_nSyncAccu;
+	u32 m_nFeedbackNominal;			// frames per packet at the nominal rate, Q16.16
 
 	u8 m_uchClockSourceID;
 	u8 m_uchSelectorUnitID;
diff --git a/lib/usb/usbaudiostreaming.cpp b/lib/usb/usbaudiostreaming.cpp
index f48056e..40bc0fb 100644
--- a/lib/usb/usbaudiostreaming.cpp
+++ b/lib/usb/usbaudiostreaming.cpp
@@ -127,6 +127,7 @@ CUSBAudioStreamingDevice::CUSBAudioStreamingDevice (CUSBFunction *pFunction)
 	m_nPacketsPerChunk (0),
 	m_bSyncEPActive (FALSE),
 	m_nSyncAccu (0),
+	m_nFeedbackNominal (0),
 	m_uchClockSourceID (USB_AUDIO_UNDEFINED_UNIT_ID),
 	m_uchSelectorUnitID (USB_AUDIO_UNDEFINED_UNIT_ID),
 	From ("uaudio")
@@ -720,6 +721,8 @@ boolean CUSBAudioStreamingDevice::Setup (unsigned nSampleRate)
 
 			m_nChunkSizeBytes = nSampleRate * nFrameSize / nUSBFrameRate;
 
+			m_nFeedbackNominal = (u32) (((u64) nSampleRate << 16) / nUSBFrameRate);
+
 			// round up to a multiple of frame size
 			m_nChunkSizeBytes += nFrameSize-1;
 			m_nChunkSizeBytes /= nFrameSize;
@@ -1066,6 +1069,18 @@ void CUSBAudioStreamingDevice::SyncCompletionHandler (CUSBRequest *pURB, void *p
 
 	assert (pThis->m_bSyncEPActive);
 
+	// Some devices send 0 or a value far from the nominal rate before their clock runs, and a
+	// chunk size derived from it would be 0 or overflow the TX buffers. As the Linux driver
+	// does, accept only values between 7/8 and 3/2 of the nominal rate.
+	if (bOK)
+	{
+		u32 nValue = bFormat10_14 ? (pThis->m_SyncEPBuffer[0] & 0xFFFFFF) << 2
+					  : pThis->m_SyncEPBuffer[0];
+		u32 nNominal = pThis->m_nFeedbackNominal;
+		bOK =    nValue >= nNominal - nNominal / 8
+		      && nValue <= nNominal + nNominal / 2;
+	}
+
 	if (bOK)
 	{
 		if (bFormat10_14)