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ON-BOARD PROGRAMMING METHODS FOR XFLASH AND HDFLASH ST7 MCUs

2 APPLICATION RUNNING DURING PROGRAMMING

This method is primarily for applications that cannot be stopped and which have to keep some

kind of software kernel running all the time (generally for security or safety reasons).

It also covers, and this is the most common reason for not using ICP, applications where the

application designer chooses alternative means of implementing the programming process,

specifically:

– The hardware connection to the programming tool, where the new firmware is stored

– The software protocol that defines the commands, status and data format.

A typical case is when a communication port already used in the application is available: It

avoids implementing an additional connector just for the ICP process: this approach is widely

used for devices with a CAN or USB interface.

Using your own protocol for on-board programming has the advantage of allowing flexibility in

terms of hardware implementation. However, some firmware must already be present on the

MCU in order to run the communication protocol: This method can thus be used only for re-

programming, which implies the MCU has been programmed at least once before with an-

other method. Another constraint is that it is not possible to reprogram the whole program

memory of the MCU: nor can the reprogramming firmware itself be altered.

ST7 STMicroelectronics MCUs with HDFLASH and XFLASH have this capability of running

user-specific firmware to perform In-Application Programming (IAP) of the MCU program

memory.

This feature not only allows the application to keep some background tasks running, but also

to allows you to use any type of communication protocol for the reprogramming process.

2.1 IAP OVERVIEW

The ST7 program memory is divided into several (up to 3) sectors. Only Sector 0 cannot be

programmed or erased in normal (user mode) operation. So this sector can be used to exe-

cute the firmware handling the reprogramming process, without being altered.

Reprogramming any of the other sectors is possible, and is based on the execution of a spe-

cific software sequence, for which a software library, the IAP driver, is provided by STMicroe-

lectronics.

The Sector 0 firmware handles the complete protocol and sequencing of the operations, and

some tasks that cannot be stopped during the programming process.

In contrast to the ICP process, the embedded hardware peripherals can be activated by the

Sector 0 firmware to carry out some background tasks. The only limitation is that the Interrupt

Requests coming from these peripherals (Reception on UART, Timer overflow, ..) can be

processed only after the IAP driver has completed the requested operations. A notable excep-