AN2792

Bootloader description

5/12

1.

Disable all interrupt sources (any peripheral managed by polling).

2.

The host can reprogram the Flash program memory and the bootloader option byte

values as shown in Table 1 according to the content of the first Flash program memory

location (8000h).

3.

When read out protection (ROP) is equal to AAh (ROP active), the Flash program

memory is read out protected. In this case, the bootloader stops and the user

application starts. If ROP is not equal to AAh, the bootloader continues to be executed.

4.

The CAN peripheral can only be used if an external clock (8 MHz, 16 MHz, or 24 MHz)

is present. It is initialized at 125 kbps. The USART, LINUART, and SPI peripherals do

not require an external clock.

5.

Set the high speed internal RC oscillator (HSI) to 16 MHz and initialize the USART and

LINUART receiver pins in input pull-up mode in the GPIO registers. Initialize the SPI in

slave mode.

6.

Interface polling: The bootloader polls the peripherals waiting for a synchronization

byte/message (SYNCHR) within a timeout of 1 s. If a timeout occurs, either the Flash

program memory is virgin in which case it waits for a synchronization byte/message in

an infinite loop, or the Flash program memory is not virgin and the bootloader restores

the registers’ reset status before going to the Flash program memory reset vector at

8000h.

Note: When synchronization fails and the bootloader receives a byte/message different

to ‘SYNCHR’, two different situations can be distinguished according to the peripheral:

With USART or LINUART, a device reset or power-down is necessary before

synchronization can be tried again.

With CAN or SPI, the user can continue to poll the interfaces until a synchronization or

a timeout occurs.

7.

If the synchronization message is received by the USART or LINUART, the bootloader

detects the baud rate and initializes the USART or LINUART respectively and goes to

step 8 below. If the synchronization message is received by the CAN or SPI, the

bootloader goes directly to step 8 below.

Note: Once one of the available interfaces receives the synchronization message, all

others are disabled.

8.

Waiting for commands: Commands are checked in an infinite loop and executed. To exit

from the bootloader, the host has to send a ‘go’ command. When this is done, the

bootloader removes the EM and WM routines from the RAM memory before jumping to

the address selected by the host.