Magtek MAGTEK User Manual download pdf (Page 56)

MagTek Communications Protocol, Driver Reference Manual

NOTIFICATIONS

MCP devices can send unsolicited messages – notifications, in case an external event occurred

(e.g. user swiped a card, pushed a button, etc.) or a device application has changed its state (e.g.

printer out of paper, command completed, etc.). Unlike command responses, notifications can be

issued by the device application at any time.

Notifications contain the identification of the device application that issued them (application

ID), the command ID, and a result code. It may also contain additional data about the event that

occurred.

The host application waits for notifications by calling McpWait. The MCP driver can block the

application until a notification arrives from the device. When the driver receives a notification

from the device, it completes the pending McpWait request providing the notification

information received from the device.

If a notification comes while the host application is not waiting for it, the MCP driver buffers the

notification until the application calls McpWait. The driver does not impose a limit on the

number of the notifications that can wait at the same time.

The McpWait function uses a timeout (dwTimeout) value to indicate how it is to return to the

host application.

Value Meaning

-1 Return with the next buffered notification or wait indefinitely for the next

notification to arrive if there are no notification buffered.

=0 Return immediately with the next buffered notification or an error if no

notifications are currently buffered. Do not wait for a notification to arrive if

no notifications are queued.

>0 Return with the next buffered notification or wait the specified number of

milliseconds for the next notification to arrive. Returns with an error if no

notifications arrive within the allotted time.

The function also can wait/check for new notifications, discard all previous notifications, or

accept notifications that happened before the time of issuing the McpWait call. The device does

not expect a response or any specific action from the host application in response to a

notification message.

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Magtek MAGTEK User Manual Page 56