User manual

LPCXpresso Experiment Kit - User’s Guide

Page 111

Place the UART related code in file uart.c, and place the function prototype declarations in file

uart.h. Do not forget to remove the retarget.c file and change back C runtime library to

Redlib (semihost).

The code is quite complex and builds on two circular buffers. The receive and transmit buffers can

have different sizes, but they must be a power of two. The reason for this is the special mask

operations (bitwise-AND with size minus 1). Characters to be transmitted should be placed in a circular

buffer. If transmission is not active, start transmission again with the first character in the buffer. As

soon as a character has been transmitted the interrupt handler checks if there are more characters to

be transmitted in the buffer. If no more, disable the transmission interrupt.

Extend the code above to also implement a uint8_t UARTGetCharBlock(void) function

that blocks until a char has been received and returns the received character. Let the new function

make use of the UARTGetChar() function.

Also update the UARTSendString() and UARTSendBuffer() functions from Lab14a. The

suggested function prototypes are as below. These functions are needed on future experiments (with

RF modules).

/*****************************************************************************

** Function name: UARTSendString

** Descriptions: Send a null-terminated string to UART 0 port

** parameters: byte to send and if call should wait for transfer to complete

** Returned value: None

*****************************************************************************/

void UARTSendString(uint8_t *pStr, uint8_t blocking);

/*****************************************************************************

** Function name: UARTSendBuffer

** Descriptions: Send a number of bytes/chars of data to UART 0 port

** parameters: data to send, number of bytes and if call is blocking

** Returned value: None

*****************************************************************************/

void UARTSendBuffer(uint8_t *pBuf, uint16_t length, uint8_t blocking);

Create an application that demonstrates receive and transmit circular buffers. The receive overflow

problem in the previous experiment can for example be handled to some extent if the buffers are large

enough.