UART library

Enumerations
enum	uart_index_t { UART0 = 0 , UART1 = 1 , NUM_UARTS }

Functions
void	uart_init (const int uart)
void	uart_destroy (const int uart)
void	uart_send (const int uart, const uint8_t data)
uint8_t	uart_recv (const int uart)
bool	uart_has_data (const int uart)
bool	uart_has_space (const int uart)
void	uart_reset_fifos (const int uart)

Detailed Description

Functions to use the Universal Asynchronous Receiver-Transmitter (UART).

Two UART channels can be instantiated, UART0 and UART1. Before sending and receiving bytes the UART must be connect to some I/O pins through the switchbox, e.g.

switchbox_set_pin(SWB_AR0, SWB_UART0_RX);
switchbox_set_pin(SWB_AR1, SWB_UART0_TX);

After that, an example of how to use this library for the MASTER.

#include <libpynq.h>
int main (void)
{
 // initialise all I/O
 pynq_init();
 
 // initialize UART 0
 uart_init(UART0);
 // flush FIFOs of UART 0
 uart_reset_fifos(UART0);
 
 uint8_t byte[] = "Hello\n";
 int i = 0;
 while (byte[i] != '\0') {
  uart_send (UART0, byte[i]);
  printf("sent byte %d\n", byte[i]);
  i++;
 }
 
  // clean up after use
  pynq_destroy();
  return EXIT_SUCCESS;
}

An example of how to use this library for the SLAVE.

#include <libpynq.h>
int main (void)
{
 // initialise all I/O
 pynq_init();
 
 // initialize UART channel 0
 uart_init(UART0);
 // flush FIFOs of UART 0
 uart_reset_fifos (UART0);
 
 printf("listening\n");
 do {
   // get a byte from UART 0
   uint8_t msg = uart_recv(UART0);
   printf("received byte %d\n", msg);
 } while (1);
 
  // clean up after use
  pynq_destroy();
  return EXIT_SUCCESS;
}

UARTs can also be used through GPIO (see gpio.h and pinmap.h). Note that GPIO numbering (SWB_UART0..SWB_UART1) is then used instead of 0..NUM_UARTS-1 (UART0..UART1).

Enumeration Type Documentation

uart_index_t

enum uart_index_t

Enum of UARTs. Functions use a switch numbered from 0..NUM_UARTS-1. Alternatively, you can use UARTi instead of just i if you find that clearer.

Enumerator
UART0
UART1
NUM_UARTS

Definition at line 107 of file uart.h.

Function Documentation

uart_destroy()

void uart_destroy

(

const int

uart

)

Close the shared memory handle for the specified UART index.

Parameters

uart	The UART index to remove from the shared memory space.

Warning

Fails with program exit if the UART channel is outside valid range.

Definition at line 3 of file uart.c.

Here is the call graph for this function:

uart_has_data()

bool uart_has_data

(

const int

uart

)

Check if the receive FIFO for the specified UART index has data available.

Parameters

uart	The UART index used to check for data.

Returns

True if the receive FIFO has data, false otherwise.

Warning

Fails with program exit if the UART channel is outside valid range.

Definition at line 6 of file uart.c.

uart_has_space()

bool uart_has_space

(

const int

uart

)

Check if the transmit FIFO for the specified UART index has space available.

Parameters

uart	The UART index to check for space.

Returns

True if the FIFO has space, false otherwise.

Warning

Fails with program exit if the UART channel is outside valid range.

Definition at line 7 of file uart.c.

uart_init()

void uart_init

(

const int

uart

)

Initialize the UART specified by the index with a shared memory handle and a buffer size of 4096 bytes.

Parameters

uart	The UART index to initialize.

Warning

Fails with program exit if the UART channel is outside valid range or when the shared memory system has not been instantiated.

Definition at line 2 of file uart.c.

Here is the call graph for this function:

uart_recv()

uint8_t uart_recv

(

const int

uart

)

Receive a byte of data from the specified UART index by waiting for the receive FIFO to have data and then reading the data from the receive buffer.

Parameters

uart	The UART index to receive data from.

Returns

The received data byte.

Warning

Fails with program exit if the UART channel is outside valid range.

Definition at line 5 of file uart.c.

uart_reset_fifos()

void uart_reset_fifos

(

const int

uart

)

This function resets both the transmit and receive FIFOs of the UART specified by the uart parameter. This can be useful when there is data stuck in the FIFOs or when the FIFOs are not behaving as expected.

Parameters

uart	The UART index of the UART whose FIFOs should be reset.

Warning

This function is specific to UARTs that have FIFOs, and will have no effect on UARTs that do not have FIFOs.

Resetting the FIFOs will result in the loss of any data that is currently in the FIFOs. Therefore, this function should be used with caution, and only when it is absolutely necessary to do so.

Fails with program exit if the UART channel is outside valid range.

Definition at line 8 of file uart.c.

uart_send()

void uart_send	(	const int	uart,
		const uint8_t	data
	)

Send a byte of data on the specified UART index by waiting for the transmit FIFO to have space and then writing the data to the transmit buffer.

Parameters

uart	The UART index to send data to.
data	The data to send to the UART index.

Warning

Fails with program exit if the UART channel is outside valid range.

Definition at line 4 of file uart.c.