问题
When using VxWorks, we are trying to access a memory mapped I/O device from a Real-Time Process.
Since RTPs have memory protection, how can I access my I/O device from one?
回答1:
There are two methods you can use to access your I/O mapped device from an RTP.
I/O Subsystem (preferred)
You essentially create a small device driver. This driver can be integrated into the I/O Subsystem of VxWorks. Once integrated, the driver is available to the RTP by simply using standard I/O operations: open, close, read, write, ioctl.
Note that "creating a device driver" doesn't have to be complicated. It could be as simple as just defining a wrapper for the ioctl function. See ioLib for more details.
Map Memory Directly (not recommended)
You can create a shared memory region via the sdOpen call. When creating the shared memory, you can specify what the physical address should be. Specify the address to be your device's I/O mapped region, and you can access the device directly.
The problem is that a shared memory region is a public object that is available to any space, and poking directly at hardware goes against the philosophy behind RTPs.
来源：https://stackoverflow.com/questions/113001/how-do-i-access-my-memory-mapped-i-o-device-fpga-from-a-rtp-in-vxworks