Fix LPC17XX and LPC40XX USB data throttling

Only clear the USB read buffer when endpointRead is called. This
allows data to be read with endpointReadResult without also allowing
USB to transfer more data. Instead additional data is transferred explicitly
with a call to endpointRead.

Author: c1728p9

features/unsupported/USBDevice/targets/TARGET_NXP/USBHAL_LPC17.cpp

@@ -275,11 +275,6 @@ uint32_t USBHAL::endpointReadcore(uint8_t endpoint, uint8_t *buffer) {
 
     LPC_USB->USBCtrl = 0;
 
-    if ((endpoint >> 1) % 3 || (endpoint >> 1) == 0) {
-        SIEselectEndpoint(endpoint);
-        SIEclearBuffer();
-    }
-
     return size;
 }
 
@@ -431,7 +426,7 @@ void USBHAL::EP0setup(uint8_t *buffer) {
 }
 
 void USBHAL::EP0read(void) {
-    // Not required
+    endpointRead(EP0OUT, MAX_PACKET_SIZE_EP0);
 }
 
 void USBHAL::EP0readStage(void) {
@@ -456,6 +451,11 @@ void USBHAL::EP0stall(void) {
 }
 
 EP_STATUS USBHAL::endpointRead(uint8_t endpoint, uint32_t maximumSize) {
+    // Don't clear isochronous endpoints
+    if ((endpoint >> 1) % 3 || (endpoint >> 1) == 0) {
+        SIEselectEndpoint(endpoint);
+        SIEclearBuffer();
+    }
     return EP_PENDING;
 }
 

features/unsupported/USBDevice/targets/TARGET_NXP/USBHAL_LPC40.cpp

@@ -276,11 +276,6 @@ uint32_t USBHAL::endpointReadcore(uint8_t endpoint, uint8_t *buffer) {
 
     LPC_USB->Ctrl = 0;
 
-    if ((endpoint >> 1) % 3 || (endpoint >> 1) == 0) {
-        SIEselectEndpoint(endpoint);
-        SIEclearBuffer();
-    }
-
     return size;
 }
 
@@ -436,7 +431,7 @@ void USBHAL::EP0setup(uint8_t *buffer) {
 }
 
 void USBHAL::EP0read(void) {
-    // Not required
+    endpointRead(EP0OUT, MAX_PACKET_SIZE_EP0);
 }
 
 void USBHAL::EP0readStage(void) {
@@ -461,6 +456,11 @@ void USBHAL::EP0stall(void) {
 }
 
 EP_STATUS USBHAL::endpointRead(uint8_t endpoint, uint32_t maximumSize) {
+    // Don't clear isochronous endpoints
+    if ((endpoint >> 1) % 3 || (endpoint >> 1) == 0) {
+        SIEselectEndpoint(endpoint);
+        SIEclearBuffer();
+    }
     return EP_PENDING;
 }