Re:Core Memory Shield for Arduino
by devwastaken on Saturday April 27, 2019 @02:22PM
(#19766884)
But on a pi, how accurate is the CPU and gpio speed? On an Arduino mega it's guaranteed to be 68.5ns give or take a tiny amount because that's how long an instruction takes for gpio bitbanging registers. This makes it possible to interface with hardware that requires this precision timing. On a pi even if you're at 700mhz constant clock, caching supposedly will mess up your timings for gpio. On top of that I haven't seen much in what the lowest stable delay is for the pi gpio.
You have me curious; how do I do baremetal on the Raspberry Pi? Which RTOS do you use?
They've got a whole stickied thread on the forums about it:
https://www.raspberrypi.org/forums/viewtopic.php?f=72&t=7226...
And I think I was totally mistaken on RTOS's, I could have sworn there was a port of FreeRTOS for the RPi but it looks like that isn't really floating around.
Re:Core Memory Shield for Arduino
by SAI_Peregrinus on Saturday April 27, 2019 @06:30PM
(#19768035)
RTAI &/or Xenomai are RTOSes based on Linux, both support ARM. Xenomai has support for the Pi Zero, Pi 2 model B, and Pi 3 Model B[1]. I've never used it, but it's probably easier than porting another OS from scratch.
[1] https://gitlab.denx.de/Xenomai/xenomai/wikis/Supported_Hardw...
The difference between the two has to do with resources, architecture, and peripherals. Arduino is a low power, low cost, low memory, low speed 8-16bit microcontroller. A raspberry pi is a complete 64 bit computing system with 1-2GB of RAM and the peripherals you'd expect on most desktops. Arduino use Atmega chips while Pis use ARM cores. You need to program in a language supported by gcc for Arduino, but RPis can use the LLVM infrastructure.