AES block processing

AN3270

18/23

Doc ID 17919 Rev 2

Figure 15. is a screenshot of block chaining mode selection.

Figure 15.

Chaining mode selection

The text received through the RS232 port is saved in a static buffer. The end of transmission

occurs when the maximum buffer size has been reached or the carriage return (enter key)

has been pressed.

The maximum buffer size is defined in main.h:

#define RX_BUFFER_SIZE

(uint16_t) 128

The following code listing (available in stm8l15x_it.c) shows how the end of transmission is

detected:

if ((RxCounter == RX_BUFFER_SIZE) || (RxBuffer[RxCounter-1] == 0x0D))

{

/* Disable the Read data register not empty interrupt */

USART_ITConfig(EVAL_COM1, USART_IT_RXNE, DISABLE);

/* Max buffer size had been reached or carriage return had been pressed */

TransferComplete = 1;

........

.......

If the received buffer size is not a multiple of 128-bit, it is padded with the pre-defined pad

character. it is defined in main.h

#define PAD_CHARACTER

(uint8_t)

0x00

The BufferInit() function (in main.c) is available for padding purposes. It checks the size of

the entered text and then pads it if necessary.