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##

# 1.1.9.4.3 DRV_USART_Open Function

## C

    DRV_HANDLE DRV_USART_Open
    (
        const SYS_MODULE_INDEX index,
        const DRV_IO_INTENT ioIntent
    )

## Summary

Opens the specified USART driver instance and returns a handle to it.

## Description

This routine opens the specified USART driver instance and provides a handle that must be provided to all other client-level operations to identify the caller and the instance of the driver. The ioIntent parameter defines how the client interacts with this driver instance.

Specifying a DRV_IO_INTENT_EXCLUSIVE will cause the driver to provide exclusive access to this client. The driver cannot be opened by any other client.

## Precondition

Function DRV_USART_Initialize must have been called before calling this function.

## Parameters

Param | Description
--- | ---
index | Identifier for the object instance to be opened
intent | Zero or more of the values from the enumeration DRV_IO_INTENT "ORed" together to indicate the intended use of the driver. See function description for details.

## Returns

If successful, the routine returns a valid open-instance handle (a number identifying both the caller and the module instance).

If an error occurs, the return value is DRV_HANDLE_INVALID. Error can occur

- if the number of client objects allocated via DRV_USART_CLIENTS_NUMBER is insufficient.
- if the client is trying to open the driver but driver has been opened exclusively by another client.
- if the driver peripheral instance being opened is not initialized or is invalid.
- if the client is trying to open the driver exclusively, but has already been opened in a non exclusive mode by another client.
- if the driver is not ready to be opened, typically when the initialize routine has not completed execution.

## Example

    DRV_HANDLE handle;

    handle = DRV_USART_Open(DRV_USART_INDEX_0, DRV_IO_INTENT_EXCLUSIVE);
    if (handle == DRV_HANDLE_INVALID)
    {
        // Unable to open the driver
        // May be the driver is not initialized or the initialization
        // is not complete.
    }

## Remarks

The handle returned is valid until the DRV_USART_Close routine is called. This routine will NEVER block waiting for hardware. If the requested intent flags are not supported, the routine will return DRV_HANDLE_INVALID. This function is thread safe in a RTOS application.