NASR-M base controller works!
I’ve started populating the board, and the base controller worked. Although my long-term plan is to use a Zephyr, for simplicity, I resorted to a quick stub firmware written with STM32Cube that activates the ATX PSU and blinks the status LED. I’ve got the (primary) power!
The ever-growing “lessons learned” list has been updated with the following:
Lesson 1 Sorting piles of tiny packages and soldering them by hand made me realize how horrifically unoptimized my BOM was. It’s a pain in the neck - literally. I promised myself to pay better attention next time.
Lesson 2 The through-hole vias in thermal pads were too small and got covered. That was the most stupid negligence I’ve discovered so far. Instead of comfortably soldering QFP pads from the bottom, I will have to use a solder paste with a preheater & hot air gun combo. While waiting for the leaded solder paste to arrive, I’ll work on the Zephyr based firmware. Next time, I’ll leave 0.8-1mm hole vias under the thermal pads to avoid this. On a sufficiently large pad, it would let me heat the package from the bottom of the board using a large thermal capacity cartridge.
Lesson 3 Head magnifiers are good but have limitations. I had to invest in a microscope. Hoping it would alleviate the pain in the neck mentioned earlier.
On the positive side, I finally put my tag-connect cable to use, and it flashed the MCU as expected. From now on, I’ll be using a tag connect instead of bulky IDC boxes.
Watching the MCU controlling the ATX unit is very satisfactory. I’ll be using ATX more in the future.
Once the soldering paste arrives, I’ll solder in the secondary power supply and clock generator.