Fix USB streaming transfers stuttering at high speeds

Author: rjonaitis

src/comms/USB/USBDMAEmulation.cpp

@@ -12,7 +12,6 @@ static constexpr int maxAsyncTransfers = 16;
 USBDMAEmulation::USBDMAEmulation(std::shared_ptr<IUSB> port, uint8_t endpoint, DataTransferDirection dir)
     : port(port)
     , counters{}
-    , lastRequestIndex(0)
     , endpoint(endpoint)
     , dir(dir)
     , continuous(false)
@@ -99,7 +98,6 @@ OpStatus USBDMAEmulation::Enable(bool enable)
     }
 
     counters.transfersCompleted = 0;
-    lastRequestIndex = 0;
 
     // for USB nothing is needed to be done to just enable DMA
     isEnabled = true;
@@ -121,7 +119,7 @@ OpStatus USBDMAEmulation::EnableContinuous(bool enable, uint32_t maxTransferSize
         return OpStatus::Success;
     // For continuous transferring, preemptively request data to be transferred
     std::unique_lock lck{ queuesMutex };
-    lastRequestIndex = 0;
+    int lastRequestIndex = 0;
     port->FlushEndpoint();
     while (!transfers.empty())
     {
@@ -144,7 +142,7 @@ void USBDMAEmulation::UpdateProducerStates()
     {
         AsyncXfer* async = pendingXfers.front();
         assert(async);
-        int timeout_ms = 100; // just checking if the transfer is complete, not waiting.
+        const int timeout_ms = 0; // just check if transfer is completed. Do not wait.
         OpStatus status = port->WaitForXfer(async->xfer, timeout_ms);
         if (status != OpStatus::Success)
             break;
@@ -154,8 +152,6 @@ void USBDMAEmulation::UpdateProducerStates()
         ++counters.transfersCompleted;
         counters.transfersCompleted &= 0xFFFF;
     }
-    if (!continuous)
-        return;
 }
 
 USBDMAEmulation::State USBDMAEmulation::GetCounters()
@@ -172,20 +168,16 @@ OpStatus USBDMAEmulation::SubmitRequest(uint64_t index, uint32_t bytesCount, Dat
     assert(bytesCount > 0);
     assert(index < mappings.size());
 
-    int count = 1;
     std::unique_lock lck{ queuesMutex };
-    count = std::min(size_t(count), transfers.size());
-    if (!transfers.empty() && count > 0)
+    if (!transfers.empty())
     {
         AsyncXfer* async = transfers.front();
         async->requestedSize = bytesCount;
         OpStatus status = port->BeginDataXfer(async->xfer, mappings[index].buffer, async->requestedSize, endpoint);
-        lastRequestIndex = index; //(lastRequestIndex + 1) % mappings.size();
         if (status != OpStatus::Success)
             return OpStatus::Error;
         transfers.pop();
         pendingXfers.push(async);
-        --count;
         return OpStatus::Success;
     }
     return OpStatus::Error;

src/comms/USB/USBDMAEmulation.h

@@ -56,7 +56,6 @@ class USBDMAEmulation : public IDMA
     std::string name;
     std::shared_ptr<IUSB> port;
     State counters;
-    uint16_t lastRequestIndex;
     uint8_t endpoint;
     DataTransferDirection dir;
     bool continuous;

src/comms/USB/UnixUsb.cpp

@@ -16,6 +16,7 @@
 #endif
 
 #include "limesuiteng/Logger.h"
+#include "threadHelper.h"
 
 using namespace std::literals::string_literals;
 
@@ -47,7 +48,6 @@ static int SessionRefCountIncrement()
         int returnCode = libusb_init(&gContextLibUsb); // Initialize the library for the session we just declared
         if (returnCode < 0)
             lime::error("UnixUsb::libusb_init Error %i", returnCode); // There was an error
-
 #if LIBUSBX_API_VERSION < 0x01000106
         libusb_set_debug(gContextLibUsb, 3); // Set verbosity level to 3, as suggested in the documentation
 #else
@@ -56,7 +56,14 @@ static int SessionRefCountIncrement()
             LIBUSB_LOG_LEVEL_INFO); // Set verbosity level to info, as suggested in the documentation
 #endif
         if (gContextLibUsb)
+        {
             gUSBProcessingThread = std::thread(HandleLibusbEvents, gContextLibUsb);
+            SetOSThreadPriority(ThreadPriority::HIGHEST, ThreadPolicy::REALTIME, &gUSBProcessingThread);
+#ifdef __linux__
+            char threadName[16] = "limeUSB"; // limited to 16 chars, including null byte.
+            pthread_setname_np(gUSBProcessingThread.native_handle(), threadName);
+#endif
+        }
     }
     return activeUSBconnections;
 }

src/streaming/TRXLooper.cpp

@@ -812,11 +812,11 @@ void TRXLooper::ReceivePacketsLoop()
                         fpgaTicks,
                         static_cast<int64_t>((diff.GetSeconds() + diff.GetFracSeconds()) * 1e9));
                 }
-                lime::debug("Loss: pkt:%li exp: %016lx, got: %016lx, diff: %li, timeDiff:%lins",
+                lime::debug("Loss: pkt:%li exp: %016lx, got: %016lx, diff: %+li, timeDiff:%+lins",
                     stats.packets + i,
                     expectedTimestamp.GetTicks(),
                     hwts.GetTicks(),
-                    expectedTimestamp.GetTicks() - hwts.GetTicks(),
+                    hwts.GetTicks() - expectedTimestamp.GetTicks(),
                     static_cast<int64_t>((diff.GetSeconds() + diff.GetFracSeconds()) * 1e9));
                 ++stats.loss;
                 loss.add(1);