@@ -115,6 +115,7 @@ FLASHMEM bool ReceiveFileData(File& file, uint32_t len, uint32_t& checksum)
             SendU16(FailToken);
             CmdChannel->printf("Rec %lu of %lu bytes\n", bytenum, len);
             file.close();
+            DiscardCmdInput(len - bytenum, millis(), len - bytenum);
             return false;
         }
         file.write(byteIn = CmdChannel->read());
@@ -209,7 +210,11 @@ FLASHMEM void PostFileCommand()
 
     SendU16(AckToken);
 
-    if (!ReceiveFileData(fileStream, fileLength, checksum)) return;
+    if (!ReceiveFileData(fileStream, fileLength, checksum))
+    {
+        sourceFS->remove(FileNamePath); //GetFileStream made it, so a retry finds no "File already exists"
+        return;
+    }
 
     SendU16(AckToken);
 
@@ -628,7 +633,7 @@ FLASHMEM bool SendFileData(File& file, uint32_t len) {
 
     Printf_dbg("[SendFileData] Complete - Sent %lu bytes\n", bytenum);
     Printf_dbg("[SendFileData] Flushing output...\n");
-    CmdChannel->flush();
+    FlushCmdChannel(CmdChannel);
     Printf_dbg("[SendFileData] Flush complete\n");
     return true;
 }
 
@@ -292,7 +292,7 @@ FLASHMEM void ServiceSerial(Stream *ThisCmdChannel)
             if(StartMicros>MaxMicros) MaxMicros=StartMicros;
             if(StartMicros<MinMicros) MinMicros=StartMicros;
             CmdChannel->printf("Took %luuS to send %d Regs\n", StartMicros, RegsInPacket);
-            CmdChannel->flush();
+            FlushCmdChannel(CmdChannel);
             delay(10); //allow scope time to re-arm
          }
          CmdChannel->printf(" %d packets, %luuS Min to %luuS Max\n", NumPackets, MinMicros, MaxMicros);
@@ -851,6 +851,13 @@ FLASHMEM bool GetUInt(uint32_t *InVal, uint8_t NumBytes)
    return true;
 }
 
+FLASHMEM void FlushCmdChannel(Stream *Channel)
+{
+   // EthernetClient::flush() and USBSerialBase::flush() wait with no deadline for the peer
+   // to ACK; the bytes are already queued to go without them.
+   if (Channel == &Serial) Serial.send_now();
+}
+
 FLASHMEM void SendU16(uint16_t SendVal)
 {
    CmdChannel->write((uint8_t)(SendVal & 0xff));
@@ -984,6 +991,23 @@ FLASHMEM void  getFreeITCM()
    //CmdChannel->printf( "ITCM DWORD cnt = %u [#bytes=%u] \n", jj, jj*4);
 }
 
+// The WriteC64Spans command's deadline for the whole command, not only SerialAvailabeTimeout's per
+// byte, which leaves every byte's wait for the peer to spend with the C64 unserved.  2 bytes/mS is
+// under every channel's rate, the 115200 baud USB host port included.  Bytes is the command's length so far.
+FLASHMEM uint32_t SpansCeilingmS(uint32_t Bytes) { return SerialTimoutMillis * 10 + Bytes / 2; }
+
+// Throws away up to Owed bytes a failed sender can still send unprompted, so they are not parsed
+// as commands.  Ends early on quiet longer than a TCP retransmit, or 2 S past SpansCeilingmS(Bytes)
+// counted from Began.  A caller with no command deadline passes millis() and Owed, so the ceiling
+// runs from the failure; WriteC64Spans passes its command's start and length, so it runs from there.
+FLASHMEM void DiscardCmdInput(uint32_t Owed, uint32_t Began, uint32_t Bytes)
+{
+   const uint32_t CeilingmS = SpansCeilingmS(Bytes) + SerialTimoutMillis * 4;
+   uint32_t Quiet = millis();
+   while (Owed && millis() - Quiet < SerialTimoutMillis * 2 && millis() - Began < CeilingmS)
+      if (CmdChannel->available()) { CmdChannel->read(); Owed--; Quiet = millis(); }
+}
+
 #ifdef Dbg_SerSD
 // SD card info, then a copy of SdFat's TeensySdioDemo speed test (examples/TeensySdioDemo), then
 // what a MinimalBoot bank swap does (LoadBank in IOH_EasyFlash.c): a seek and one 8K read, timed in uS.
@@ -1209,7 +1233,6 @@ struct DMAStage
 FLASHMEM void WriteC64MemCommand() 
 {
    uint32_t DMAAddr, DMALength;
-   const uint32_t Began = millis();
 
    if (!GetUInt(&DMAAddr, 2))
    {
@@ -1231,7 +1254,7 @@ FLASHMEM void WriteC64MemCommand()
    {
       SendU16(FailToken);
       CmdChannel->printf("No memory to stage %lu bytes\n", DMALength);
-      DiscardCmdInput(DMALength, Began, DMALength);  // sent unprompted, and not to be read as commands
+      DiscardCmdInput(DMALength, millis(), DMALength);  // sent unprompted, and not to be read as commands
       return;
    }
 
@@ -1241,6 +1264,7 @@ FLASHMEM void WriteC64MemCommand()
       {
          SendU16(FailToken);
          CmdChannel->println("Error receiving data!");
+         DiscardCmdInput(DMALength - ByteNum, millis(), DMALength - ByteNum);
          return;
       }
       DMABuf[ByteNum] = CmdChannel->read();
@@ -1272,21 +1296,6 @@ FLASHMEM void WriteC64MemCommand()
    //Serial.printf("DMA Write: addr $%04x:$%04x (%lu Bytes)\n", DMAAddr, DMAAddr+DMALength-1, DMALength);
 }
 
-// One deadline for the whole command, not only SerialAvailabeTimeout's per byte, which leaves
-// every byte's wait for the peer to spend with the C64 unserved.  2 bytes/mS is under every
-// channel's rate, the 115200 baud USB host port included.  Bytes is the command's length so far.
-FLASHMEM uint32_t SpansCeilingmS(uint32_t Bytes) { return SerialTimoutMillis * 10 + Bytes / 2; }
-
-// Throws away up to Owed bytes a failed sender can still send unprompted, so they are not parsed
-// as commands.  Ends early on quiet longer than a TCP retransmit, or 2 S past the command's deadline.
-FLASHMEM void DiscardCmdInput(uint32_t Owed, uint32_t Began, uint32_t Bytes)
-{
-   const uint32_t CeilingmS = SpansCeilingmS(Bytes) + SerialTimoutMillis * 4;
-   uint32_t Quiet = millis();
-   while (Owed && millis() - Quiet < SerialTimoutMillis * 2 && millis() - Began < CeilingmS)
-      if (CmdChannel->available()) { CmdChannel->read(); Owed--; Quiet = millis(); }
-}
-
 // After is what the sender goes on to send without waiting for a reply.  On false a FailToken
 // has gone out.  Patient waits out a pause under the command's deadline alone, rather than
 // SerialAvailabeTimeout's per byte.
 
@@ -299,7 +299,7 @@ void loop()
 #ifdef DbgIOTraceLog
       PrintResetSnapshot();
 #endif
-      CmdChannel->flush();
+      FlushCmdChannel(CmdChannel);
       delay(50); 
       uint32_t NextInterval = 10000, beginWait = millis();
       bool LEDState = true, DefEEPReboot = false;