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Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
@Gordon
It's not random - it's just that unlike something like the USART, it has a fixed clock divisor that's /2, /4, /8, /16, etc.
Every Espruino board would be the same, however between different STM32 devices that have different clock speeds (eg, 48Mhz instead of 72Mhz), it could be quite different.
At the moment it's just SPI MOSI that you can use (there are a few pins that do this) because the SPI hardware is used to get the fast pulses while the software works out what bytes to send. With some extra work on Espruino it'd be possible to send the data in software only (on any pin), but the idea is that eventually the SPI hardware can be sending the data out more or less automatically while Espruino can get on with doing more calculations.