After powerup, have you ever initialized a character display using C code? From scratch or library calls?

The classic part is the Hitachi HD44780 (and compatible) character LCD controller. Initializing it from scratch — driving the parallel bus (RS, R/W, E, and 4 or 8 data lines) directly — requires following the documented power-on init sequence carefully, because the controller's internal state after power-up is not guaranteed and the busy flag is not yet reliable.

A correct from-scratch init for 4-bit mode looks like:

1. Wait after power-up (typically >15–40 ms after VCC rises) for the controller to stabilize.
2. Force 8-bit mode three times to put the interface into a known state: send Function Set 0x30, wait >4.1 ms; send 0x30 again, wait >100 µs; send 0x30 a third time. (These early commands must use fixed delays because the busy flag can't be polled yet.)
3. Switch to 4-bit interface: send 0x20.
4. Function Set: set 4-bit/8-bit, number of lines (1 or 2), and font (5×8 or 5×10), e.g. 0x28 for 4-bit, 2-line, 5×8.
5. Display OFF: 0x08.
6. Clear Display: 0x01 (this one is slow, ~1.5–2 ms).
7. Entry Mode Set: 0x06 (increment cursor, no shift).
8. Display ON: 0x0C (display on, cursor/blink as desired).

After init, respect the busy flag (or fixed per-command delays if R/W is tied low) between commands, and remember that Clear and Home are much slower than other commands. Each nibble in 4-bit mode is clocked with a high-to-low pulse on the E line. Whether done "from scratch" with bit-banged GPIO or via a vendor/HAL library, the same sequence and timing constraints apply — libraries just hide the nibble-packing and delays.