Creates an I/O request.

Item CreateIOReq( const char *name, uint8 pri, Item dev, Item mp )

This convenience procedure creates an I/O request item.

When you create an I/O request, you must decide how the device will notify you when an I/O operation completes. There are two choices:

• Notification by signal
• Notification by message

With notification by signal, the device will send your task the SIGF_IODONE signal whenever an I/O operation completes. This is a low-overhead mechanism, which is also low on information. When you get the signal, all you know is that an I/O operation has completed. You do not know which operation has completed. This has to be determined by looking at the state of all outstanding I/O requests.

Notification by message involves slightly more overhead, but provides much more information. When you create the I/O request, you indicate a message port. Whenever an I/O operation completes, the device will send a message to that message port. The message will contain the following information:

• msg_Result Contains the io_Error value from the I/O request. This indicates the state of the I/O operation, whether it worked or failed.
• msg_DataPtr Contains the item number of the I/O request that completed.
• msg_DataSize Contains the value of the ioi_User field taken from the IOInfo structure used when initiating the I/O operation.

• name The name of the I/O request (see “Notes”).

• pri The priority of the I/O request. For some device drivers, this value determines the order in which I/O requests are processed. When in doubt about what value to use, use 0.

• dev The item number of the device to which to send the I/O request.

• mp If a task wants to receive a message when an I/O request is finished, this argument must be the item number of the message port to receive the message. If the task wants to receive a signal when an I/O request is finished instead of a message, this argument must be 0.

The procedure returns the item number of the new I/O request or one of the following error codes if an error occurs:

• BADITEM The mp argument was not zero but did not specify a valid message port.

• ER_Kr_ItemNotOpen The device specified by the dev argument is not open.

• NOMEM There was not enough memory to complete the operation.

Convenience call implemented in clib.lib V20.

• io.h ANSI C Prototype

• clib.lib ARM Link Library

When you no longer need an I/O request, use DeleteIOReq() to delete it.

You can use FindNamedItem() to find a I/O request by name. When creating I/O requests, you should assign unique names whenever possible.

The kernel may change the priority of an I/O request to help optimize throughput.

DeleteIOReq()