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# uartlite v1_14_a

This component contains the implementation of the XUartLite component which is the driver for the Xilinx UART Lite device. This UART is a minimal hardware implementation with minimal features. Most of the features, including baud rate, parity, and number of data bits are only configurable when the hardware device is built, rather than at run time by software.

The device has 16 byte transmit and receive FIFOs and supports interrupts. The device does not have any way to disable the receiver such that the receive FIFO may contain unwanted data. The FIFOs are not flushed when the driver is initialized, but a function is provided to allow the user to reset the FIFOs if desired.

The driver defaults to no interrupts at initialization such that interrupts must be enabled if desired. An interrupt is generated when the transmit FIFO transitions from having data to being empty or when any data is contained in the receive FIFO.

In order to use interrupts, it's necessary for the user to connect the driver interrupt handler, XUartLite_InterruptHandler, to the interrupt system of the application. This function does not save and restore the processor context such that the user must provide it. Send and receive handlers may be set for the driver such that the handlers are called when transmit and receive interrupts occur. The handlers are called from interrupt context and are designed to allow application specific processing to be performed.

The functions, XUartLite_Send and XUartLite_Recv, are provided in the driver to allow data to be sent and received. They are designed to be used in polled or interrupt modes.

The driver provides a status for each received byte indicating any parity frame or overrun error. The driver provides statistics which allow visibility into these errors.

Initialization & Configuration

The XUartLite_Config structure is used by the driver to configure itself. This configuration structure is typically created by the tool-chain based on HW build properties.

To support multiple runtime loading and initialization strategies employed by various operating systems, the driver instance can be initialized in one of the following ways:

- XUartLite_Initialize(InstancePtr, DeviceId) - The driver looks up its own configuration structure created by the tool-chain based on an ID provided by the tool-chain.

- XUartLite_CfgInitialize(InstancePtr, CfgPtr, EffectiveAddr) - Uses a configuration structure provided by the caller. If running in a system with address translation, the provided virtual memory base address replaces the physical address present in the configuration structure.

RTOS Independence

This driver is intended to be RTOS and processor independent. It works with physical addresses only. Any needs for dynamic memory management, threads or thread mutual exclusion, virtual memory, or cache control must be satisfied by the layer above this driver.

Note:

The driver is partitioned such that a minimal implementation may be used. More features require additional files to be linked in.

     MODIFICATION HISTORY:

     Ver   Who  Date     Changes
     ----- ---- -------- -----------------------------------------------
     1.00a ecm  08/31/01 First release
     1.00b jhl  02/21/02 Repartitioned the driver for smaller files
     1.01a jvb  12/14/05 I separated dependency on the static config table and
                         xparameters.h from the driver initialization by moving
                         _Initialize and _LookupConfig to _sinit.c. I also added
                         the new _CfgInitialize routine.
     1.02a rpm  02/14/07 Added check for outstanding transmission before
                         calling the send callback (avoids extraneous
                         callback invocations) in interrupt service routine.
     1.12a mta  03/31/07 Updated to new coding conventions
     1.13a sv   01/21/08 Updated driver to support access through DCR bus
     1.14a sdm  08/22/08 Removed support for static interrupt handlers from the MDD
    		      file
     1.14a sdm  09/26/08 Updated code to avoid race condition in
    		      XUartLite_SendBuffer

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