Improved electronic calibration

- Added automatic port detection mode
- Faster coefficient readout
- LibreCAL using asynchronous libusb API

Software/PC_Application/LibreVNA-GUI/Util/usbinbuffer.cpp

@@ -0,0 +1,109 @@
+#include "usbinbuffer.h"
+
+#include <mutex>
+
+#include <QDebug>
+
+using namespace std;
+
+USBInBuffer::USBInBuffer(libusb_device_handle *handle, unsigned char endpoint, int buffer_size) :
+    buffer_size(buffer_size),
+    received_size(0),
+    inCallback(false),
+    cancelling(false)
+{
+    buffer = new unsigned char[buffer_size];
+    memset(buffer, 0, buffer_size);
+    transfer = libusb_alloc_transfer(0);
+    libusb_fill_bulk_transfer(transfer, handle, endpoint, buffer, buffer_size, CallbackTrampoline, this, 0);
+    libusb_submit_transfer(transfer);
+}
+
+USBInBuffer::~USBInBuffer()
+{
+    if(transfer) {
+        cancelling = true;
+        libusb_cancel_transfer(transfer);
+        // wait for cancellation to complete
+        mutex mtx;
+        unique_lock<mutex> lck(mtx);
+        using namespace std::chrono_literals;
+        if(cv.wait_for(lck, 100ms) == cv_status::timeout) {
+            qWarning() << "Timed out waiting for mutex acquisition during disconnect";
+        }
+    }
+    delete[] buffer;
+}
+
+void USBInBuffer::removeBytes(int handled_bytes)
+{
+    if(!inCallback) {
+        throw runtime_error("Removing of bytes is only allowed from within receive callback");
+    }
+    if(handled_bytes >= received_size) {
+        received_size = 0;
+    } else {
+        // not removing all bytes, have to move remaining data to the beginning of the buffer
+        memmove(buffer, &buffer[handled_bytes], received_size - handled_bytes);
+        received_size -= handled_bytes;
+    }
+}
+
+int USBInBuffer::getReceived() const
+{
+    return received_size;
+}
+
+void USBInBuffer::Callback(libusb_transfer *transfer)
+{
+    if(cancelling || (transfer->status == LIBUSB_TRANSFER_CANCELLED)) {
+        // destructor called, do not resubmit
+        libusb_free_transfer(transfer);
+        this->transfer = nullptr;
+        cv.notify_all();
+        return;
+    }
+    switch(transfer->status) {
+    case LIBUSB_TRANSFER_COMPLETED:
+    case LIBUSB_TRANSFER_TIMED_OUT:
+        if(transfer->actual_length > 0) {
+            received_size += transfer->actual_length;
+            inCallback = true;
+            emit DataReceived();
+            inCallback = false;
+        }
+        break;
+    case LIBUSB_TRANSFER_NO_DEVICE:
+        qCritical() << "LIBUSB_TRANSFER_NO_DEVICE";
+        libusb_free_transfer(transfer);
+        return;
+    case LIBUSB_TRANSFER_ERROR:
+    case LIBUSB_TRANSFER_OVERFLOW:
+    case LIBUSB_TRANSFER_STALL:
+        qCritical() << "LIBUSB_ERROR" << transfer->status;
+        libusb_free_transfer(transfer);
+        this->transfer = nullptr;
+        emit TransferError();
+        return;
+        break;
+    case LIBUSB_TRANSFER_CANCELLED:
+        // already handled before switch-case
+        break;
+    }
+    // Resubmit the transfer
+    transfer->buffer = &buffer[received_size];
+    transfer->length = buffer_size - received_size;
+    transfer->length = (transfer->length / 512) * 512;
+    libusb_submit_transfer(transfer);
+}
+
+void USBInBuffer::CallbackTrampoline(libusb_transfer *transfer)
+{
+    auto usb = (USBInBuffer*) transfer->user_data;
+    usb->Callback(transfer);
+}
+
+uint8_t *USBInBuffer::getBuffer() const
+{
+    return buffer;
+}