stm8-bootloader

Serial bootloader for STM8S microcontrollers. A detailed write-up on this bootloader is posted here.

Features

• small - fits in 547 bytes (SDCC v3.6.8 #9951)
• fast - uploads 4k binary in 1 second @115200bps
• configurable - can be adjusted for parts with different flash block size

Configuration

The default configuration targets low-density devices (STM8S003). Configuration is located in config.h.

• BLOCK_SIZE - flash block size according to device datasheet. This should be set to 64 for low-density devices or 128 for devices with >8k flash.
• BOOT_ADDR - application boot address.
• BOOT_PIN - entry jumper. This is set to PD3 by default.
• RELOCATE_IVT - when set to 1 (default) the interrupt vectors are relocated. When set to 0 the bootloader will overwrite it's own interrupt vector table with the application's IVT, thus eliminating additional CPU overhead during interrupts. Write-protection cannot be used in this case and resulting binary is slightly larger.

Changing boot address

Boot address must be a multiple of BLOCK_SIZE. Address is set in 2 places:

• config.h
• init.s

Main application is compiled with --code-loc <address> option. When RELOCATE_IVT is set to 0, 0x80 must be subtracted from application address and isr29 must be implemented: void dummy_isr() __interrupt(29) __naked { ; }.

Build instructions

Build and flash the bootloader:

$ make && make flash

Enable write-protection (UBC) on pages 0-9:

$ make opt-set

Uploading the firmware

There is a demo application inside app directory which toggles PD4 via interrupts. To upload the application short PD3 to ground, power-cycle the MCU and run the uploader utility. DTR pin on UART-USB converter can be connected to RESET pin on STM8 for automatic reset.

$ cd app && make
$ python ../uploader/boot.py -p /dev/ttyUSB0 firmware.bin

Porting

TBD