diff options
Diffstat (limited to 'LUFA/Drivers/USB/Class/Device/CDC.h')
| -rw-r--r-- | LUFA/Drivers/USB/Class/Device/CDC.h | 14 |
1 files changed, 9 insertions, 5 deletions
diff --git a/LUFA/Drivers/USB/Class/Device/CDC.h b/LUFA/Drivers/USB/Class/Device/CDC.h index 9e92d5f6c..3ada8f7af 100644 --- a/LUFA/Drivers/USB/Class/Device/CDC.h +++ b/LUFA/Drivers/USB/Class/Device/CDC.h @@ -233,7 +233,10 @@ uint8_t CDC_Device_SendByte(USB_ClassInfo_CDC_Device_t* const CDCInterfaceInfo, const uint8_t Data) ATTR_NON_NULL_PTR_ARG(1); - /** Determines the number of bytes received by the CDC interface from the host, waiting to be read. + /** Determines the number of bytes received by the CDC interface from the host, waiting to be read. This indicates the number + * of bytes in the OUT endpoint bank only, and thus the number of calls to \ref CDC_Device_ReceiveByte() which are guaranteed to + * succeed immediately. If multiple bytes are to be received, they should be buffered by the user application, as the endpoint + * bank will not be released back to the USB controller until all bytes are read. * * \pre This function must only be called when the Device state machine is in the DEVICE_STATE_Configured state or * the call will fail. @@ -245,17 +248,18 @@ uint16_t CDC_Device_BytesReceived(USB_ClassInfo_CDC_Device_t* const CDCInterfaceInfo) ATTR_NON_NULL_PTR_ARG(1); /** Reads a byte of data from the host. If no data is waiting to be read of if a USB host is not connected, the function - * returns 0. The \ref CDC_Device_BytesReceived() function should be queried before data is received to ensure that no data - * underflow occurs. + * returns a negative value. The \ref CDC_Device_BytesReceived() function may be queried in advance to determine how many + * bytes are currently buffered in the CDC interface's data receive endpoint bank, and thus how many repeated calls to this + * function which are guaranteed to succeed. * * \pre This function must only be called when the Device state machine is in the DEVICE_STATE_Configured state or * the call will fail. * * \param[in,out] CDCInterfaceInfo Pointer to a structure containing a CDC Class configuration and state. * - * \return Next received byte from the host, or 0 if no data received. + * \return Next received byte from the host, or a negative value if no data received. */ - uint8_t CDC_Device_ReceiveByte(USB_ClassInfo_CDC_Device_t* const CDCInterfaceInfo) ATTR_NON_NULL_PTR_ARG(1); + int16_t CDC_Device_ReceiveByte(USB_ClassInfo_CDC_Device_t* const CDCInterfaceInfo) ATTR_NON_NULL_PTR_ARG(1); /** Flushes any data waiting to be sent, ensuring that the send buffer is cleared. * |