Phil Elwell

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The annotation say 2.9us, which is pretty short. With the 250MHz core clock the fastest SPI clock is 125MHz, but in practice you'd struggle to get much more than 50MHz...

The bcm2835 SPI driver uses software CS control - the CS line is just any random GPIO - which contributes to the delay.

As an experiment, put `force_turbo=1` in config.txt and reboot.

I don't think you are going to improve without rewriting the driver. I note that you've not shown two back-to-back transfers - for how long is CS high?

I'm sure a kernel driver could reduce at least the inter-transfer delay, but I don't have a feel for how much. Before investing time in that direction it might be...

I doubt you'll be able to improve the situation very much - the kernel SPI subsystem and drivers don't intentionally waste time. Even if you could reduce the best-case interval...

> most kernel messages (until systemd takes over) are available The kernel command line (cmdline.txt) parameter `ignore_loglevel` prints all kernel messages to the console, even after systemd has started.