UARTDRV - UART Driver#

Universal Asynchronous Receiver/Transmitter Driver.

The source files for the UART driver library, uartdrv.c and uartdrv.h, are in the emdrv/uartdrv folder.

Introduction#

The UART driver supports the UART capabilities of the USART, UART, and LEUART peripherals. The driver is fully reentrant and supports multiple driver instances. The driver does not buffer or queue data. However, it queues UART transmit and receive operations. Both blocking and non-blocking transfer functions are available. Non-blocking transfer functions report transfer completion with callback functions. Transfers are done using DMA. Simple direct/forced transmit and receive functions are also available. Note that these functions are blocking and not suitable for low energy applications because they use CPU polling.

UART hardware flow control (CTS/RTS) is fully supported by the driver. UART software flow control (XON/XOFF) is partially supported by the driver. For more information about flow control support, see Flow Control Support.

Note

• Transfer completion callback functions are called from within the DMA interrupt handler with interrupts disabled.

Configuration Options#

Some properties of the UARTDRV driver are compile-time configurable. These properties are set in a uartdrv_config.h file. A template for this file, containing default values, is in the emdrv/config folder. To configure UARTDRV for your application, provide a custom configuration file, or override the defines on the compiler command line. These are the available configuration parameters with default values defined.

  // Set to 1 to enable hardware flow control.
#define EMDRV_UARTDRV_FLOW_CONTROL_ENABLE       1

  // Maximum number of driver instances.
#define EMDRV_UARTDRV_MAX_DRIVER_INSTANCES      4

  // UART software flow control code: request peer to start Tx.
#define UARTDRV_FC_SW_XON                       0x11

  // UART software flow control code: request peer to stop Tx.
#define UARTDRV_FC_SW_XOFF                      0x13

The properties of each UART driver instance are set at run-time via the UARTDRV_InitUart_t data structure input parameter to the UARTDRV_InitUart() function for UART and USART peripherals, and the UARTDRV_InitLeuart_t data structure input parameter to the UARTDRV_InitLeuart() function for LEUART peripherals.

The API#

This section contains brief descriptions of the functions in the API. For more information on input and output parameters and return values, click on the hyperlinked function names. Most functions return an error code, ECODE_EMDRV_UARTDRV_OK is returned on success, see ecode.h and uartdrv.h for other error codes.

The application code must include uartdrv.h header file.

UARTDRV_InitUart(), UARTDRV_InitLeuart() and UARTDRV_DeInit()
These functions initialize and deinitialize the UARTDRV driver. Typically, UARTDRV_InitUart() (for UART/USART) or UARTDRV_InitLeuart() (for LEUART) are called once in the startup code.

UARTDRV_GetReceiveStatus() and UARTDRV_GetTransmitStatus()
Query the status of a current transmit or receive operations. Reports number of items (frames) transmitted and remaining.

UARTDRV_GetReceiveDepth() and UARTDRV_GetTransmitDepth()
Get the number of queued receive or transmit operations.

UARTDRV_Transmit(), UARTDRV_Receive()
UARTDRV_TransmitB(), UARTDRV_ReceiveB()
UARTDRV_ForceTransmit() and UARTDRV_ForceReceive()
Blocking and non-blocking transfer functions are included. The blocking versions have an uppercase B (for Blocking) at the end of their function name. Blocking functions do not return before the transfer is complete. The non-blocking functions signal a transfer completion with a callback function. UARTDRV_ForceTransmit() and UARTDRV_ForceReceive() are also blocking. These two functions access the UART peripheral directly without using DMA or interrupts. UARTDRV_ForceTransmit() does not respect flow control. UARTDRV_ForceReceive() forces RTS low.

UARTDRV_Abort()
Abort current transmit or receive operations and remove all queued operations.

UARTDRV_FlowControlSet(), UARTDRV_FlowControlGetSelfStatus(), UARTDRV_FlowControlSetPeerStatus() and UARTDRV_FlowControlGetPeerStatus()
Set and get flow control status of self or peer device. Note that the return value from these two functions depends on the flow control mode set by UARTDRV_FlowControlSet(), UARTDRV_InitUart(), or UARTDRV_InitLeuart().

UARTDRV_FlowControlIgnoreRestrain()
Enables transmission when restrained by flow control.

UARTDRV_PauseTransmit() and UARTDRV_ResumeTransmit()
Pause a currently active transmit operation by preventing the DMA from loading the UART FIFO. Will not override HW flow control state (if applicable), but can be used in conjunction.

Flow Control Support#

If UART flow control is not required, make sure that EMDRV_UARTDRV_FLOW_CONTROL_ENABLE is set to 0. This reduces the code size and complexity of the driver.

Both hardware and software flow control are supported. To enable either of these, set EMDRV_UARTDRV_FLOW_CONTROL_ENABLE to 1 in uartdrv_config.h.

Hardware Flow Control#

UART hardware flow control uses two additional pins for flow control handshaking, the clear-to-send (CTS) and ready-to-send (RTS) pins. RTS is an output and CTS is an input. These are active-low signals. When CTS is high, the UART transmitter should stop sending frames. A receiver should set RTS high when it is no longer capable of receiving data.

• Peripheral Hardware Flow Control#

Newer devices natively support CTS/RTS in the USART peripheral hardware. To enable hardware flow control, perform the following steps:

• Set EMDRV_UARTDRV_FLOW_CONTROL_ENABLE to 1.

• In the UARTDRV_InitUart_t struct passed to UARTDRV_InitUart(), set UARTDRV_InitUart_t.fcType = uartdrvFlowControlHwUart.

• Define the pins for CTS and RTS by setting ctsPort, ctsPin, rtsPort and rtsPin in the init struct.

• Also define the CTS and RTS locations by setting portLocationCts and portLocationRts in the init struct.

• GPIO Hardware Flow Control#

To support hardware flow control on devices that don't have UART CTS/RTS hardware support, the driver includes the GPIOINT driver to emulate a hardware implementation of UART CTS/RTS flow control on these devices.

To enable hardware flow control, perform the following steps:

• Set EMDRV_UARTDRV_FLOW_CONTROL_ENABLE to 1.

• UART/USART: In the UARTDRV_InitUart_t struct passed to UARTDRV_InitUart(), set UARTDRV_InitUart_t.fcType = uartdrvFlowControlHw.

• LEUART: In the UARTDRV_InitLeuart_t struct passed to UARTDRV_InitLeuart(), set UARTDRV_InitLeuart_t::fcType = uartdrvFlowControlHw.

• Define the pins for CTS and RTS by setting ctsPort, ctsPin, rtsPort and rtsPin in the same init struct.

Note

• Because of the limitations in GPIO interrupt hardware, you cannot select CTS pins in multiple driver instances with the same pin number. For example, pin A0 and B0 cannot serve as CTS pins in two concurrent driver instances.

RTS is set high whenever there are no Rx operations queued. The UART transmitter is halted when the CTS pin goes high. The transmitter completes the current frame before halting. DMA transfers are also halted.

Software Flow Control#

UART software flow control uses in-band signaling, meaning the receiver sends special flow control characters to the transmitter and thereby removes the need for dedicated wires for flow control. The two symbols UARTDRV_FC_SW_XON and UARTDRV_FC_SW_XOFF are defined in uartdrv_config.h.

To enable support for software flow control, perform the following steps:

• Set EMDRV_UARTDRV_FLOW_CONTROL_ENABLE to 1.

• UART/USART: In the UARTDRV_InitUart_t structure passed to UARTDRV_InitUart(), set UARTDRV_InitUart_t.fcType = uartdrvFlowControlSw.

• LEUART: In the UARTDRV_InitLeuart_t structure passed to UARTDRV_InitLeuart(), set UARTDRV_InitLeuart_t::fcType = uartdrvFlowControlSw.

Note

• Software flow control is partial only.

The application must monitor buffers and make decisions on when to send XON/ XOFF. XON/XOFF can be sent to the peer using UARTDRV_FlowControlSet(). Though UARTDRV_FlowControlSet() will pause the active transmit operation to send a flow control character, there is no way to guarantee the order. If the application implements a specific packet format where the flow control codes may appear only in fixed positions, the application should not use UARTDRV_FlowControlSet() but implement read and write of XON/XOFF into packet buffers. If the application code fully implements all the flow control logic, EMDRV_UARTDRV_FLOW_CONTROL_ENABLE should be set to 0 to reduce code space.

Example#

Modules#

UARTDRV_Buffer_t

UARTDRV_Buffer_FifoQueue_t

UARTDRV_InitLeuart_t

UARTDRV_InitEuart_t

UARTDRV_HandleData_t

Error Codes

Status Codes