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Handle receiving a ZLP in USB_Available #6886

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Handle receiving a ZLP in USB_Available #6886

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12 changes: 11 additions & 1 deletion hardware/arduino/avr/cores/arduino/USBCore.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -171,6 +171,11 @@ static inline u8 FifoFree()
return UEINTX & (1<<FIFOCON);
}

static inline u8 HasOUT()
{
return UEINTX & (1<<RXOUTI);
}

static inline void ReleaseRX()
{
UEINTX = 0x6B; // FIFOCON=0 NAKINI=1 RWAL=1 NAKOUTI=0 RXSTPI=1 RXOUTI=0 STALLEDI=1 TXINI=1
Expand Down Expand Up @@ -214,7 +219,12 @@ class LockEP
u8 USB_Available(u8 ep)
{
LockEP lock(ep);
return FifoByteCount();
u8 n = FifoByteCount();

if (!n && HasOUT())
ReleaseRX(); // handle ZLP

return n;
}

// Non Blocking receive
Expand Down