Before the electronic products are shipped from the factory, the application code can be easily downloaded to the MCU through the offline burner, the programming fixture, or the online burner through the reserved programming interface. However, if the product has been sold or not on the R&D side, how do you upgrade the program? Today, we will introduce the online upgrade method through IAP.
First understand the two concepts of ISP and IAP:
1. ISP (In-System Programming) is programmable in the system. It means that the blank device on the circuit board can be programmed into the end user code without removing the device from the circuit board. The programmed device can also be wiped by ISP. Except or reprogramming;
2, IAP (In-Application Programming) means that the MCU can acquire new code in the system and reprogram itself, then the program can be used to change the program.
IAP programming implementation
To implement the IAP function, you need to write two programs when designing the product. The first part of the program does not perform normal functions. It only receives firmware or new applications through some communication method (such as USB, Uart), and executes the second program. Part of the code update, we call it Bootloader; the second part of the code is the user's application code to achieve the real function of the product. The first part of the code must be programmed in advance (via the programmer or emulator) into the microcontroller. The second part of the code can be programmed by the programmer or emulator, or it can be programmed using the IAP function of the first part. After the chip is powered on, the first part of the code is first run. If no update is needed, the second part of the code is executed. If it is detected that the update is needed, the update program is executed, and after the update is completed, the second part of the code is executed. Take STM32 as an example, as shown below:
As shown in the above example, the bootloader's starting address is stored at 0x08000000 (also the starting address of the STM32 chip Flash). After the program is executed, it jumps to the reset interrupt entry vector address and then jumps to the main load of the bootloader. To upgrade the program, execute the second part of the application code to the flash area with address 0x08000000 + N. After the update is complete, jump to the second part of the application's reset interrupt vector address (0x08000004 + N +M), then jump Go to the main function of the second part of the application. During the running of the main function, if the CPU encounters an interrupt request, the PC pointer is forced to jump to the interrupt vector table of the bootloader (0x08000004 in the figure above) instead of the second part. The interrupt vector table, the program then jumps to the new interrupt service routine corresponding to the interrupt source according to the offset vector table offset we set, and returns to the main function of the second part of the application after the execution is completed.
The points to note are: the address of the first part of the program (Bootloader) jumps and the start address of the second part of the application must be consistent, the corresponding interrupt vector table should also be modified, otherwise the program will not run correctly.
to sum up
Through IAP in application programming, after some products are released, it is convenient to update and upgrade the firmware program in the product through a reserved communication port (such as USB, serial port, network port or wireless transmission). Before using the IAP function, the chip must first burn the Bootloader that implements the IAP function into the microcontroller through the programming tool. If the bootloader program is corrupted, the product must be returned to the factory to reprogram the program, which is cumbersome and time consuming and costly. In response to such a requirement, the STM32 automatically sets the first 4 pages of the user's Flash area to write protection while performing read protection on the Flash area, which can effectively ensure that the IAP program area is not accidentally destroyed.
ZLG Zhiyuan Electronics' P800isp is a multi-channel online offline burner. Users only need to reserve the programming interface of the product. With P800isp, the program can be burned once and updated twice, even if the product bootloader is Destruction can also easily solve the update problem.
Easy Electronic Technology Co.,Ltd , https://www.yxpcelectronicgroups.com