UhClem

Almost makes sense. The dynamic range of the value is small so a float is wasted on it and fixed point is perfect. But 64 bits is way too big and for fixed point you would multiply by a power of two. Like 2^23. Which would provide a range of +255...

I don't know. But I did take a dive into the code generated and it does add delay. Not in a way that appeals to me but it does do it.

Without the the Arduino environment, you have to do a lot more. I haven't tried the Teesy4.1 but I have done this with the 3.6. For even more fun, I did it in assembly language.

That should work.

A hazard here is that the target uses the CS pin to select between I2C and SPI. Which means that the devices that aren't selected are looking for I2C things to be happening. Depending on what clock and data are doing, that could be a problem...

I wonder how the library slows things down so that it meets the setup, hold, and clock cycle times of the SSD1309. On slow parts I wouldn't worry too much but with these really fast ARM devices, it matters.

The manual at 20.3.2 describes the low voltage detector. Where during a low power reset you store a magic number in a particular register. The hardware then compares that to the known correct value. A difference triggers a low voltage violation...

The Teensy 4.1 RTC looks kind of complicated. Looking at the data sheet I see a Real Time Counter but not a Real Time Clock. With there actually being two counters. A low power counter that runs from the battery and a high power counter. With...

I thought that the SD library only did 50MHz for the SD clock. This is faster than that.

5us to write 512 bytes. Excellent trick. What interface are you using?

A count of writes. In this case it is the same as the number of blocks. (512 bytes)

It has been a while but I have done testing where I just tested the card. No file system involved at all. Just my code writing sequential blocks. My usual method was to have a timer running and I would write the current count into the buffer...

My take on eForth for the Teensy 3.6, and a logger is on my web site: http://davesrocketworks.com/electronics/logger/eforth.html

It has been a while so I looked up the notes I made when adding interrupts to my version of Forth. "The ARM stacks up a bunch of registers: R0-R3,R12,LR,PC,PSR" This is handy as r0-r3 can be clobbered so aren't saved by a function. Any...

SD writes can take randomly long times so you must have sufficient buffer space. How long? Very long. See the maximum FAT write time in the SD specification for example. (750ms!) I tested this once long ago... Longer buffers (power of 2 * 512)...