Suggestions on how to handle boards with slow RTCs?

Hello!

I'm currently playing with driving an HD44780 with a SiFive HiFive1 RevB. Its RTC is only 32_786 Hz, and so is too slow for a DelayUs impl. I have a fork where I've changed all the DelayUs<u16> trait bounds to DelayMs<u16> and changed all the delay.delay_us(100) calls to delay.delay_ms(1_u8) calls, which seems to work. This is, of course, a terrible hack, so I'm curious what your thoughts are for supporting boards with slow RTCs.

In terms of prior art, there's another fork which uses a separate bus module for the board they're working on, relying on I2C.

I'd love to hear your thoughts on this.

I experimented some more last night after filing this issue, which revealed some oddities. First, occasionally when writing data to the LCD, a character will not render properly. One of the specific ways this manifests is that sometimes a 'z' will render as an 'r'. Looking at the datasheet provided by Adafruit (pp 17-18), these are represented by 0b0111_1010 and 0b0111_0010 respectively on the HD44780. The code I'm using is anahata0108/lcd_fiddle if you want to take a look at what I'm doing.

I have some other boards to play with (like an Uno) and I'll see if I can reproduce the same bug with them. The HiFive1 RevB is known for having a slow RTC, and some other oddities, so I'll do some more digging.

[ColinTimBarndt]

Delay implements DelayUs now in version 0.11.0: https://docs.rs/e310x-hal/0.11.0/e310x_hal/delay/struct.Delay.html#impl-DelayUs%3Cu8%3E-for-Delay