1394 Node-Targeted Asynchronous Transfers

To understand Windows 1394 asynchronous transfer operation, one must understand the different types of addressing modes that the Windows 1394 bus driver uses. Addressing modes determine how the bus driver interprets destination address information that is passed along with asynchronous transfer requests. For Windows 2000 and earlier platforms, there were two modes of addressing when using asynchronous transfers normal-mode and raw-mode. What these modes are and how they work is explained later. For XP and later platforms, there is a new addressing mode called virtual-mode addressing. Virtual-mode addressing is used for 1394 virtual devices. The virtual device mechanism for 1394 was introduced with the Windows XP 1394 bus driver stack. In order to fully understand 1394 asynchronous communication on Windows platforms, it is helpful to understand what 1394 virtual devices are and how they are used. In a moment, I will take a step to the side and cover virtual devices in some detail. As for asynchronous transfer addressing modes, none of these were documented in the Windows Device Driver Development Kit (DDK) help until about a year ago. Even now the documentation does not explain how one goes about implementing some of these modes. The following paragraphs will attempt to explain asynchronous addressing modes, and show some code that demonstrates how to go about implementing the different modes in a WDM device driver. First, let us look at 1394 virtual devices. If you do not care about 1394 virtual devices or if you are already familiar with them, you can just skip down to the section titled Asynchronous Transfers.


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