Hi,
The paper "An I/O System for Mach 3.0" gives very short description of
the user-level device management:
Devices can be managed from user-level by vectoring all device
interrupts out to an application's thread. The kernel maps to user space
the device's registers, a shared page containing some control
information, and some memory for handling DMA to/from the device. When
an interrupt comes, a small interrupt routine saves any volatile
register state in the shared page for later use by the user code, and
then dismisses the interrupt, typically by disabling the interrupt
enable bit in the device, or by reading an "interrupt-acknowledge"
register. When the user thread runs it just invokes the driver's
interrupt routine as if it were handling the interrupt in kernel-mode.
After all necessary processing, the thread then re-enables interrupts in
the device.
I have several questions:
* I suppose we can map to the user space the device's registers, etc, by
using device_map, but I don't know how to do it in practice.
* Does the small interrupt routine in the kernel already exists?
* What is the programming interface provided by the kernel to the
user-level device driver? Is it still the same set of functions:
device_* in device.defs?
Zheng Da
