This example compiles by SDCC (tested v4.0.0) and works with STM8 SPL (STSW-STM8069) v2.3.1 patched by STM8-SPL_SDCC_patch.
The LED connected to the PA1 pin. It's how the LED connected on the STM8S001J3 tiny board.
To delay function uses the timer TIM4, CPU runs on 16Mhz.
To flash firmware to STM8S001J3 MCU uses ST-Link and stm8flash tool.
The compiled ihx firmware for STM8S001J3 can be downloaded from Releases section. The last version can be downloaded by the blink_heartbeat_spl.ihx link.
To flash it through stm8flash and ST-Link programmer just run:
stm8flash -c stlinkv2 -p stm8s001j3 -w blink_heartbeat_spl.ihx
make
make flash
If needed use the command make size to get the size of the binary firmware before actually flashing into MCU.