diff --git a/cdcacm.cpp b/cdcacm.cpp
index 08f9ac7b..87fb421b 100644
--- a/cdcacm.cpp
+++ b/cdcacm.cpp
@@ -278,39 +278,84 @@ uint8_t ACM::Poll() {
 }
 
 uint8_t ACM::RcvData(uint16_t *bytes_rcvd, uint8_t *dataptr) {
-        return pUsb->inTransfer(bAddress, epInfo[epDataInIndex].epAddr, bytes_rcvd, dataptr);
+        uint8_t rv;
+        rv = pUsb->inTransfer(bAddress, epInfo[epDataInIndex].epAddr, bytes_rcvd, dataptr);
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
 }
 
 uint8_t ACM::SndData(uint16_t nbytes, uint8_t *dataptr) {
-        return pUsb->outTransfer(bAddress, epInfo[epDataOutIndex].epAddr, nbytes, dataptr);
+        uint8_t rv;
+        rv = pUsb->outTransfer(bAddress, epInfo[epDataOutIndex].epAddr, nbytes, dataptr);
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
 }
 
 uint8_t ACM::SetCommFeature(uint16_t fid, uint8_t nbytes, uint8_t *dataptr) {
-        return ( pUsb->ctrlReq(bAddress, 0, bmREQ_CDCOUT, CDC_SET_COMM_FEATURE, (fid & 0xff), (fid >> 8), bControlIface, nbytes, nbytes, dataptr, NULL));
+        uint8_t rv;
+        rv = ( pUsb->ctrlReq(bAddress, 0, bmREQ_CDCOUT, CDC_SET_COMM_FEATURE, (fid & 0xff), (fid >> 8), bControlIface, nbytes, nbytes, dataptr, NULL));
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
 }
 
 uint8_t ACM::GetCommFeature(uint16_t fid, uint8_t nbytes, uint8_t *dataptr) {
-        return ( pUsb->ctrlReq(bAddress, 0, bmREQ_CDCIN, CDC_GET_COMM_FEATURE, (fid & 0xff), (fid >> 8), bControlIface, nbytes, nbytes, dataptr, NULL));
+        uint8_t rv;
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
+        rv = ( pUsb->ctrlReq(bAddress, 0, bmREQ_CDCIN, CDC_GET_COMM_FEATURE, (fid & 0xff), (fid >> 8), bControlIface, nbytes, nbytes, dataptr, NULL));
 }
 
 uint8_t ACM::ClearCommFeature(uint16_t fid) {
-        return ( pUsb->ctrlReq(bAddress, 0, bmREQ_CDCOUT, CDC_CLEAR_COMM_FEATURE, (fid & 0xff), (fid >> 8), bControlIface, 0, 0, NULL, NULL));
+        uint8_t rv;
+        rv = ( pUsb->ctrlReq(bAddress, 0, bmREQ_CDCOUT, CDC_CLEAR_COMM_FEATURE, (fid & 0xff), (fid >> 8), bControlIface, 0, 0, NULL, NULL));
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
 }
 
 uint8_t ACM::SetLineCoding(const LINE_CODING *dataptr) {
-        return ( pUsb->ctrlReq(bAddress, 0, bmREQ_CDCOUT, CDC_SET_LINE_CODING, 0x00, 0x00, bControlIface, sizeof (LINE_CODING), sizeof (LINE_CODING), (uint8_t*)dataptr, NULL));
+        uint8_t rv;
+        rv = ( pUsb->ctrlReq(bAddress, 0, bmREQ_CDCOUT, CDC_SET_LINE_CODING, 0x00, 0x00, bControlIface, sizeof (LINE_CODING), sizeof (LINE_CODING), (uint8_t*)dataptr, NULL));
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
 }
 
 uint8_t ACM::GetLineCoding(LINE_CODING *dataptr) {
-        return ( pUsb->ctrlReq(bAddress, 0, bmREQ_CDCIN, CDC_GET_LINE_CODING, 0x00, 0x00, bControlIface, sizeof (LINE_CODING), sizeof (LINE_CODING), (uint8_t*)dataptr, NULL));
+        uint8_t rv;
+        rv = ( pUsb->ctrlReq(bAddress, 0, bmREQ_CDCIN, CDC_GET_LINE_CODING, 0x00, 0x00, bControlIface, sizeof (LINE_CODING), sizeof (LINE_CODING), (uint8_t*)dataptr, NULL));
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
 }
 
 uint8_t ACM::SetControlLineState(uint8_t state) {
-        return ( pUsb->ctrlReq(bAddress, 0, bmREQ_CDCOUT, CDC_SET_CONTROL_LINE_STATE, state, 0, bControlIface, 0, 0, NULL, NULL));
+        uint8_t rv;
+        rv = ( pUsb->ctrlReq(bAddress, 0, bmREQ_CDCOUT, CDC_SET_CONTROL_LINE_STATE, state, 0, bControlIface, 0, 0, NULL, NULL));
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
 }
 
 uint8_t ACM::SendBreak(uint16_t duration) {
-        return ( pUsb->ctrlReq(bAddress, 0, bmREQ_CDCOUT, CDC_SEND_BREAK, (duration & 0xff), (duration >> 8), bControlIface, 0, 0, NULL, NULL));
+        uint8_t rv;
+        rv = ( pUsb->ctrlReq(bAddress, 0, bmREQ_CDCOUT, CDC_SEND_BREAK, (duration & 0xff), (duration >> 8), bControlIface, 0, 0, NULL, NULL));
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
 }
 
 void ACM::PrintEndpointDescriptor(const USB_ENDPOINT_DESCRIPTOR* ep_ptr) {
diff --git a/cdcftdi.cpp b/cdcftdi.cpp
index f0f5d0d1..ccc46e36 100644
--- a/cdcftdi.cpp
+++ b/cdcftdi.cpp
@@ -182,7 +182,7 @@ uint8_t FTDI::Init(uint8_t parent, uint8_t port, bool lowspeed) {
 
         USBTRACE("FTDI configured\r\n");
 
-        bPollEnable = true;
+        ready = true;
         return 0;
 
 FailGetDevDescr:
@@ -254,6 +254,7 @@ uint8_t FTDI::Release() {
         bNumEP = 1;
         qNextPollTime = 0;
         bPollEnable = false;
+        ready = false;
         return pAsync->OnRelease(this);
 }
 
@@ -275,7 +276,7 @@ uint8_t FTDI::Poll() {
 uint8_t FTDI::SetBaudRate(uint32_t baud) {
         uint16_t baud_value, baud_index = 0;
         uint32_t divisor3;
-
+        uint8_t rv = 0;
         divisor3 = 48000000 / 2 / baud; // divisor shifted 3 bits to the left
 
         if(wFTDIType == FT232AM) {
@@ -306,27 +307,56 @@ uint8_t FTDI::SetBaudRate(uint32_t baud) {
         }
         USBTRACE2("baud_value:", baud_value);
         USBTRACE2("baud_index:", baud_index);
-        return pUsb->ctrlReq(bAddress, 0, bmREQ_FTDI_OUT, FTDI_SIO_SET_BAUD_RATE, baud_value & 0xff, baud_value >> 8, baud_index, 0, 0, NULL, NULL);
+        rv = pUsb->ctrlReq(bAddress, 0, bmREQ_FTDI_OUT, FTDI_SIO_SET_BAUD_RATE, baud_value & 0xff, baud_value >> 8, baud_index, 0, 0, NULL, NULL);
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
 }
 
 uint8_t FTDI::SetModemControl(uint16_t signal) {
-        return pUsb->ctrlReq(bAddress, 0, bmREQ_FTDI_OUT, FTDI_SIO_MODEM_CTRL, signal & 0xff, signal >> 8, 0, 0, 0, NULL, NULL);
+        uint8_t rv;
+        rv = pUsb->ctrlReq(bAddress, 0, bmREQ_FTDI_OUT, FTDI_SIO_MODEM_CTRL, signal & 0xff, signal >> 8, 0, 0, 0, NULL, NULL);
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
 }
 
 uint8_t FTDI::SetFlowControl(uint8_t protocol, uint8_t xon, uint8_t xoff) {
-        return pUsb->ctrlReq(bAddress, 0, bmREQ_FTDI_OUT, FTDI_SIO_SET_FLOW_CTRL, xon, xoff, protocol << 8, 0, 0, NULL, NULL);
+        uint8_t rv;
+        rv = pUsb->ctrlReq(bAddress, 0, bmREQ_FTDI_OUT, FTDI_SIO_SET_FLOW_CTRL, xon, xoff, protocol << 8, 0, 0, NULL, NULL);
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
 }
 
 uint8_t FTDI::SetData(uint16_t databm) {
-        return pUsb->ctrlReq(bAddress, 0, bmREQ_FTDI_OUT, FTDI_SIO_SET_DATA, databm & 0xff, databm >> 8, 0, 0, 0, NULL, NULL);
+        uint8_t rv;
+        rv = pUsb->ctrlReq(bAddress, 0, bmREQ_FTDI_OUT, FTDI_SIO_SET_DATA, databm & 0xff, databm >> 8, 0, 0, 0, NULL, NULL);
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
 }
 
 uint8_t FTDI::RcvData(uint16_t *bytes_rcvd, uint8_t *dataptr) {
-        return pUsb->inTransfer(bAddress, epInfo[epDataInIndex].epAddr, bytes_rcvd, dataptr);
+        uint8_t rv;
+        rv = pUsb->inTransfer(bAddress, epInfo[epDataInIndex].epAddr, bytes_rcvd, dataptr);
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
 }
 
 uint8_t FTDI::SndData(uint16_t nbytes, uint8_t *dataptr) {
-        return pUsb->outTransfer(bAddress, epInfo[epDataOutIndex].epAddr, nbytes, dataptr);
+        uint8_t rv;
+        rv = pUsb->outTransfer(bAddress, epInfo[epDataOutIndex].epAddr, nbytes, dataptr);
+        if(rv && rv != hrNAK) {
+                Release();
+        }
+        return rv;
 }
 
 void FTDI::PrintEndpointDescriptor(const USB_ENDPOINT_DESCRIPTOR* ep_ptr) {
diff --git a/cdcftdi.h b/cdcftdi.h
index f6ee7e8c..435891da 100644
--- a/cdcftdi.h
+++ b/cdcftdi.h
@@ -105,7 +105,8 @@ class FTDI : public USBDeviceConfig, public UsbConfigXtracter {
         uint8_t bNumIface; // number of interfaces in the configuration
         uint8_t bNumEP; // total number of EP in the configuration
         uint32_t qNextPollTime; // next poll time
-        bool bPollEnable; // poll enable flag
+        volatile bool bPollEnable; // poll enable flag
+        volatile bool ready; //device ready indicator
         uint16_t wFTDIType; // Type of FTDI chip
         uint16_t wIdProduct; // expected PID
 
@@ -141,10 +142,9 @@ public:
                 return (vid == FTDI_VID && pid == FTDI_PID);
         }
         virtual bool isReady() {
-                return bPollEnable;
+                return ready;
         };
 
-
 };
 
 #endif // __CDCFTDI_H__