Serial Port Driver Architecture (Windows Embedded CE 6.0)
1/6/2010
The serial port driver handles any I/O devices that behave like serial ports, including those based on 16450 and 16550 universal asynchronous receiver-transmitter (UART) chips and those that use direct memory access (DMA). Many hardware platforms have devices of this type, including ordinary 9-pin serial ports, infrared I/O ports, and PC Card serial devices, such as modems. If multiple types of serial ports exist on a hardware platform, you can either create several different serial drivers, one for each serial port type, or create several different lower layers and link them to a single upper layer. This creates one multipurpose serial driver. Creating separate drivers can simplify debugging and maintenance because each driver supports only one type of port. Creating a multipurpose driver, such as the sample serial port driver, is more complex but gives a small memory savings.
The COM_Open function in the serial port upper layer does not implement the fErrorChar, fNull, and fAbortOnChar members of the DCB structure. You must add support for this functionality in your lower layer, if it is appropriate for your serial port hardware.
Because the functionality of serial ports maps to the functionality provided by standard stream interface functions, the serial port driver uses the stream interface as its device interface.
Serial port devices make extensive use of I/O control codes to set and query various attributes of a serial port. For example, there are I/O control codes for setting and clearing the Data Terminal Ready (DTR) line, for purging any undelivered data and for getting the status of a modem device. Therefore, you should support as many serial I/O control codes as possible in your implementation of COM_IOControl.