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keirf / greaseweazle

Tools for accessing a floppy drive at the raw flux level
The Unlicense
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Beware of 4 MHz STM32 models #11

Closed nretro closed 4 years ago

nretro commented 4 years ago

I bought a STM32F103C8T6 from China on ebay. On close examination, the description says

4-16MHz crystal.

and in fact has a 4 MHz instead of an 8 MHz crystal. The blinky test succeeds nicely, but only at half speed (output at 57600 baud).

STM32F103C8_4MHZ

keirf commented 4 years ago

I figure I ought to be able to measure HSE against the HSI or LSI oscillators and then set things up correctly for 4 vs 8 mhz crystal...

turnkit commented 4 years ago

Is there a proper forum for non bug issues?

Will the black pill work just fine too?

https://www.cnx-software.com/2019/12/24/stm32-black-pill-board-features-stm32f4-cortex-m4-mcu-optional-spi-flash/

keirf commented 4 years ago

There is a Facebook group. The black pill should work but note the pin arrangement is different. The few black pills I purchased had fake stm32 which didn't work.

cbrunschen commented 4 years ago

I think @turnkit meant the different, new "black pill", perhaps more properly the ""WeAct v1.3", that is based on an STM32F4x1 chip, see the link they posted, with a USB-C connector for visual differentiation if nothing else.

keirf commented 4 years ago

It would need porting but could then work. I didn't spot any of these new ones on ebay yet.

cbrunschen commented 4 years ago

It seems they're mainly available on Aliexpress (for example 1, 2, 3, 4) at the moment.

ptor commented 4 years ago

If someone who has ordered a verified working one (a blue, or the new black pill) from a "cheap" source (ebay or Aliexpress) could link to where they bought it from, I would be eternally grateful. I've been on the fence for a long time since I simply don't dare buy one - it looks like it's hit or miss.

nretro commented 4 years ago

Just get a Greaseweazle F730 DYI Kit from Keir. He posts them for a couple of pounds. Just send him an email. Not the cheapest way, but you definitely get a working one while supporting the project.

I've also made some progress on the 4MHz problem. Due to PLL limitations, you only can get the max speed of 72MHz on the STM32, when using 6, 8 or 12 MHz crystals. But it's easy to source these crystals cheaply and replacing them should not be a problem.

keirf commented 4 years ago

Not much more to say here then. I haven't had any more reports of 4MHz crystals. If there are then I will consider updating the docs, or make Blinky aware of it.