User manual

LPCXpresso Experiment Kit - User’s Guide

Page 50

Figure 22 – Semihosting Console Output

Create a program that determines the Endianness of the microcontroller and prints the result. Assume

we have a 32-bit number: 0x0AC0FFEE in hexadecimal notation. The table below illustrates how the

bytes are stored differently between a big and little Endian system.

Memory address

n+1

n+2

n+3

Big-endian

0x0A

0xC0

0xFF

0xEE

Little-endian

0xEE

0xFF

0xC0

0x0A

Now think of a solution how to test this.

Tip: Create an unsigned int-pointer and an unsigned char-pointer. Let these pointers point to the same

unsigned int-variable. Write a value in the unsigned int-variable with the unsigned int-pointer. Then

read out the four parts via the unsigned char-pointer.

What Endian does the LPC111x has (little or big endian)? ___________________________

The printf() function works like normal. It is possible to output strings and general expressions. Verify

that this works.

Note that Semihosting affects code execution performance severely. Every time a data transfer takes

place, the execution of the program stops during the transfer. The microcontroller cannot do anything

useful whilst waiting on each transfer to complete. The blocking time depends on the LPCXpresso IDE

(and the PC it executes on). Do not use printf() and Semihosting in time critical loops. In the next lab, a

performance test will be carried out to get a feeling for the transfer rate.

Adding printf()-functionality to a small embedded system is a trade-off between flexibility and code

size. The full implementation of printf() is very large, especially if floating point is supported. NXP has

created an application note that covers basic techniques to reduce the size of code. Many things are

covered along with a reduced size printf()-implementation that is supported in the LPCXPresso IDE.

The application note is named: AN10963: Reducing code size for LPC11XX with LPCXpresso