Remora for RP2040

Bari got me thinking about porting Remora to the RP2040 (Raspberry Pi Pico) so I ordered a Wiznet W5500-EVB-Pico evaluation board to take with me while travelling for work. $21 AUD later and only a few days local shipping it had arrived.

So, first weekend OS killing some time, the toolchain is installed and the Ethernet UDP communications is up and going. I don't have a Linux machine with me so I might have to try a virtual machine to see if I can test the comms with the LinuxCNC component.

Next step is to figure out the best approach for the thread timing. The RP2040 alarm system looks a bit clunky so another method of generating precise interrupts will be needed.

github.com/scottalford75/Remora-RP2040-W5500

Hey Scott. The rp2040 port of Grblhal uses the PIO to generate the step interrupt as well as the step waveform. It has less IRQ overhead than pure software stepping and the step generation is well suited to the fixed interrupt timing of remora.

github.com/grblHAL/RP2040/blob/master/driverPIO.pio#L8

I think there is a good solution using PWM wrap interrupts. Basically using the hardware PWM modules (slices) as a timer as each slice can generate a wrap interrupt.

Need to convert the C code into the Remora timer module, but looking good so far.

The plan will be to use the second core in the RP2040 to run the base thread. Hopefully this will allow a faster thread as the first core can handle the Ethernet stuff and the slower and less time critical servo thread tasks.

 

drewnabobber wrote:

Hey Scott. The rp2040 port of Grblhal uses the PIO to generate the step interrupt as well as the step waveform. It has less IRQ overhead than pure software stepping and the step generation is well suited to the fixed interrupt timing of remora.

github.com/grblHAL/RP2040/blob/master/driverPIO.pio#L8

I did have a quick look at the code earlier when I was thinking on options. The PIO is a bit of a mystery, but very capable. Not sure how to implement the DDS stepgen that dithers (averages) the frequency to overcome the underlying fixed clock frequency.

The advantage of using the Remora software step generator is that it can be assigned to any available pin using the config file. This would allow people to have total flexibility. And with a second core kicking around, we may as well give it a job to do

In case you have not come across this in your travels:

vanhunteradams.com/Pico/Steppers/Lorenz.html

Some more progress on the RP2040 with W5500 yesterday. The hotel cleaners must wonder what the hell the bundle of wires and blinking circuit boards are when they come. After spending most of the day getting LinuxCNC running on a VM and able to send UDP packets out from the host, communication to the RP2040 with the W5500 is up and running. But following errors... not just minor. What the? Below is a Pulseview capture of the threads running with 3 step generators and a blinky on the servo thread. Looks ok, with some fitter on the base thread (need to figure that out).