### Xilinx Processor IP Library

<hl>Software Drivers</hl>

Main Page | Data Structures | File List | Data Fields | Globals

# uartns550 v1_13_a

This driver supports the following features in the Xilinx 16450/16550 compatible UART.

- Dynamic data format (baud rate, data bits, stop bits, parity)
- Polled mode
- Interrupt driven mode
- Transmit and receive FIFOs (16 bytes each for the 16550)
- Access to the external modem control lines and the two discrete outputs

The only difference between the 16450 and the 16550 is the addition of transmit and receive FIFOs in the 16550.

Initialization & Configuration

The XUartNs550_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:

- XUartNs550_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.

- XUartNs550_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.

Baud Rate

The UART has an internal baud rate generator that is clocked at a specified input clock frequency. Not all baud rates can be generated from some clock frequencies. The requested baud rate is checked using the provided clock for the system, and checked against the acceptable error range. An error may be returned from some functions indicating the baud rate was in error because it could not be generated.

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 for any of the following conditions.

- Transmit FIFO is empty
- Data in the receive FIFO equal to the receive threshold
- Data in the receiver when FIFOs are disabled
- Any receive status error or break condition detected
- Data in the receive FIFO for 4 character times without receiver activity
- A change of a modem signal

The application can control which interrupts are enabled using the SetOptions function.

In order to use interrupts, it is necessary for the user to connect the driver interrupt handler, XUartNs550_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. A handler must be set for the driver such that the handler is called when interrupt events occur. The handler is called from interrupt context and is designed to allow application specific processing to be performed.

The functions, XUartNs550_Send() and XUartNs550_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.

Note:

The default configuration for the UART after initialization is:

- 19,200 bps or XPAR_DEFAULT_BAUD_RATE if defined
- 8 data bits
- 1 stop bit
- no parity
- FIFO's are enabled with a receive threshold of 8 bytes

     MODIFICATION HISTORY:

     Ver   Who  Date     Changes
     ----- ---- -------- -----------------------------------------------
     1.00a ecm  08/16/01 First release
     1.00b jhl  03/11/02 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.
     1.11a sv   03/20/07 Updated to use the new coding guidelines.
     1.11a sv   07/25/08 Corrected the definitions of XUN_MODEM_DCD_DELTA_MASK
     		      and XUN_MODEM_DCD_MASK.
     1.12a sdm  08/22/08 Removed support for static interrupt handlers from the MDD
    		      file
     1.12a sdm  12/15/08 Deprecated the CLOCK_HZ parameter in mdd and updated the
    		      Tcl to obtain the bus frequency during libgen
     1.13a sdm  07/10/09 a) Updated the driver Tcl to obtain the external clock
                            frequency from MHS, when C_HAS_EXTERNAL_XIN = 1.
                         b) Added receive line interrupt option to OptionsTable[]
                            in xuartns550_options.c

Copyright © 1995-2009 Xilinx, Inc. All rights reserved.