altos: Windows sends USB Out packets of 0 length. Ack them.

This was an untested case as no other operating system sents 0-length
out packets (they're not necessary). The correct response is to ACK
them by clearing the OUTPKT_RDY bit so that another packet can be sent.

Signed-off-by: Keith Packard <keithp@keithp.com>

diff --git a/src/ao_usb.c b/src/ao_usb.c
index b55130f2b73366dff311d0130133eb5b5b05ddc3..b4e3f1fe6aa3364bd7925458d6e58af28f4922e8 100644 (file)
--- a/src/ao_usb.c
+++ b/src/ao_usb.c
@@ -383,8 +383,11 @@ ao_usb_pollchar(void) __critical
                if ((USBCSOL & USBCSOL_OUTPKT_RDY) == 0)
                        return AO_READ_AGAIN;
                ao_usb_out_bytes = (USBCNTH << 8) | USBCNTL;
-               if (ao_usb_out_bytes == 0)
+               if (ao_usb_out_bytes == 0) {
+                       USBINDEX = AO_USB_OUT_EP;
+                       USBCSOL &= ~USBCSOL_OUTPKT_RDY;
                        return AO_READ_AGAIN;
+               }
        }
        --ao_usb_out_bytes;
        c = USBFIFO[AO_USB_OUT_EP << 1];