@leppieI noticed that it's strongly dependent on optimization. For start it took my
for based delay exactly 10 cycles, so when I expected to get 1 ms delay i got 10ms, pretty bang on. That was my main worry, I expected 2, maybe 3 cycles, not 10 :O But after some playing around 180 000
for loop executions took arount 7ms...
@dannyfThere's not much to explain, as just got surprised how many c cycles can empty
for take

As now I've got SysTick working, I'm going to give I2C a go

Once more, thanks for your help and explanations, jumping from AVR to STM32 with 2 weeks playing around with STM8 is fun
EDIT://updateSo, beware, I'll probably need some advice soon

Setting up I2C is not as straigt-forward as expected, first problem I encountered is that start and stop are generated, but nothing in between. after some

tweaking I get something on SDA, but SCL- zero, null, nada :O I'll link logic signals from Saleae
