ECU Flash Programming

A Flash Bootloader module is designed to update the firmware without using of any specialized hardware such as JTAG. The Flash Bootloader module is the first software module that gets activated during the booting of the system (after the power supply of the device is switched on).

Primary Bootloader: Microcontroller Unit Setup.

After the microcontroller is reset, the control first comes to Primary Bootloader. This is the part of the Bootloader software that initializes and sets up the MCU resources.

Secondary Bootloader: Microcontroller Reprogramming

Similar to the primary Bootloader that initializes various functionalities, there is another part of the Bootloader software that gets active upon receiving the firmware update via the communication medium. It is known as the Secondary Bootloader.

Essentially, this secondary Bootloader downloads the updates related to the target application and reprograms the flash memory. It has all the necessary flash routines and the UDS functions (if the Bootloader is UDS based) that are necessary for storing the updated data on the flash memory. The Primary Bootloader transfers the control to the Secondary Bootloader, once the application update is received. Next, the secondary Bootloader initializes Flash Bus Interface Unit (FBUI) on the RAM memory. This enables the capability to read/write on the flash memory.

Immediately after this step, the communication over CAN is initialized again, so that the Bootloader is ready to receive the UDS request. Post this, the update is stored in the flash memory. This is when the Secondary Bootloader is erased from the RAM and control once again goes to the Primary Bootloader.

Role of UDS Software Stack in an Automotive ECU Reprogramming

According to the AUTOSAR Standard, Unified Diagnostics Services (UDS) is the most suitable protocol for implementing Bootloader, for the purpose of ECU reprogramming.

• UDS sets the server into a reprogramming mode and start the reprogramming sequence
• It handles the initiation and termination of the data transfer
• UDS takes care of size and order of data blocks to be sent/received and memory blocks where the data will be stored
• The UDS services allow the client to start or stop a routine, which may be running on the server
• It allows the client to initiate a software reset event on the server
• UDS performs all these responsibilities with the help of certain software services. Some of these services and their use in flashing in explained in the table below.
• There are multiple reasons for that and we would discuss them in detail in other UDS blogs. For now, we will focus on the role played by UDS in a Bootloader operation.

Following are the key responsibilities of UDS in an ECU flashing operation: