stmhal: Fix USB CDC not flushing packets when an exact multiple of 64.

dpgeorge · dpgeorge · commit 09bbe7215a70 · 2014-05-10T18:56:16.000+01:00
Need to send a zero-sized packet after sending an exact multiple of 64 bytes (not just after sending 64 bytes exactly). Addresses issue adafruit#494, part 2.
diff --git a/stmhal/usbd_cdc_interface.c b/stmhal/usbd_cdc_interface.c
@@ -313,7 +313,7 @@ void USBD_CDC_HAL_TIM_PeriodElapsedCallback(void) {
             // the host waits for all data to arrive (ie, waits for a packet < max packet size).
             // To flush a packet of exactly max packet size, we need to send a zero-size packet.
             // See eg http://www.cypress.com/?id=4&rID=92719
-            UserTxNeedEmptyPacket = (buffsize == CDC_DATA_FS_MAX_PACKET_SIZE && UserTxBufPtrOutShadow == UserTxBufPtrIn);
+            UserTxNeedEmptyPacket = (buffsize > 0 && buffsize % CDC_DATA_FS_MAX_PACKET_SIZE == 0 && UserTxBufPtrOutShadow == UserTxBufPtrIn);
         }
     }
 }

Original file line number	Diff line number	Diff line change
`@@ -313,7 +313,7 @@ void USBD_CDC_HAL_TIM_PeriodElapsedCallback(void) {`
`313`	`313`	`// the host waits for all data to arrive (ie, waits for a packet < max packet size).`
`314`	`314`	`// To flush a packet of exactly max packet size, we need to send a zero-size packet.`
`315`	`315`	`// See eg http://www.cypress.com/?id=4&rID=92719`
`316`		`- UserTxNeedEmptyPacket = (buffsize == CDC_DATA_FS_MAX_PACKET_SIZE && UserTxBufPtrOutShadow == UserTxBufPtrIn);`
	`316`	`+ UserTxNeedEmptyPacket = (buffsize > 0 && buffsize % CDC_DATA_FS_MAX_PACKET_SIZE == 0 && UserTxBufPtrOutShadow == UserTxBufPtrIn);`
`317`	`317`	`}`
`318`	`318`	`}`
`319`	`319`	`}`