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Darwin 0.2 Driver Kit

			NRW DMA - driver usage
			
DMA procedure, block mode devices
{
	shut down possible DMA in progress, dequeue descriptors (not 
		normally done);
	/*
	 * enable interrupts at device/channel level. Output devices
	 * should rely on device-level I/O complete interrupts; input
	 * devices can use DMA descriptor interrupts.
	 */
	enable device error and all channel interrupts;
	if output operation 
		enable device I/O complete interrupts;
	enqueue the dma frame, enabling descriptor interrupt for input only;
	assert reset_chan and chan_{input,output};
	enable interrupt notification at kernel level;
	assert load_desc;
	assert enable_chan;
	enable device-specific logic;
	wait for interrupt or timeout;
	if any errors (timeout, channel errors, device-specific errors) {
		error recovery;
	}
	else if input operation {
		if descriptor interrupt {
			/* I/O Complete */
			clear descriptor interrupt bit;
			dequeue DMA frame;
		}
		else {
			spurious interrupt (error);
		}
	}
	else {
		if Device I/O complete interrupt {
			/* I/O Complete */
			clear device interrupt bit;
			dequeue DMA frame;
		}
		else {
			spurious interrupt (error);
		}
	}
}

DMA procedure, Streaming mode devices
{
	/*
	 * initialize channel for normal operation.
	 */
	assert reset_chan and chan_{input,output};
	enable device error and all channel interrupts;
	
	/*
	 * Main loop, run forever.
	 */
	while(1) {
		wait for interrupt or new command;
		if(new command) {
			enqueue the DMA frame, enabling descriptor interrupt
				and interrupt notification;
			if descriptor list empty {
				assert load_desc;
				assert enable_chan;
			}
			if device logic idle
				enable device-specific logic;
		}
		else {
			/*
			 * Interrupt. 
			 */
			if any errors (timeout, channel errors, 
			    device-specific errors) {
				error recovery;
			}
			else if descriptor interrupt {
			
				/*
				 * Dequeue all completed frames.
				 */
				clear descriptor interrupt bit;
				do {
					dequeue_frame(completed only, enable
						interrupts if no more);
					I/O complete for that frame;
				} while(descriptors available);
			}
			else {
				spurious interrupt;
			}
		}
	}
}

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