The frequency of caravel and user area is fixed to 10MHz or is there a way to reduce this frequency?

There are a couple of options. If you install a 2-pin header on J6 on the Caravel development board, then installing a shunt on the header will turn off the 10MHz oscillator; then you can feed your own (3.3V) clock signal to pin

xclk

. If you want to drive that signal from the Nucleo board, then install another 2-pin header on J11; a shunt on that header will connect

xclk

to the Nucleo board pin

TIM3_CH2

Thanks @Tim Edwards One more question: do I need to enable user are power or it's enabled by default? I am testing the design with nucleo board atm.

Depends on what power supply you used for your project. Because the most common configuration by far is to have the (digital) user project powered off of

vccd1

(a 1.8V domain), there is a header J3 that already has a wire across the pins. Only if you don't want

vccd1

connected up to the rest of the 1.8V domain, cut through the trace with a knife. For the other domains

vccd2

(1.8V),

vdda1

(3.3V), and

vdda2

(3.3V) (and also, redundantly, for

vccd1

), the row of 10 pins along the bottom of the Caravel development board has each domain neighboring a pin with the most common supply voltage for that domain (

3V3

and

1V8

pins). Those domains are not connected by default, so if you need them powered up you'll need to install a header on that row and put yet more shunts in.

I have used vccd1(1.8V) and if I got you right. This domain is powered off by default and I have to enable it?

No, by default

vccd1

is wired to the 1.8V supply

1V8

and you don't need to do anything.

Alright!

@Tim Edwards May I ask what do you mean to single-step the clock from

mpremote

on the Nucleo board (at the Micropython prompt)? How do I use the below code to drive the clock, for example, which file should I add these code to?

from io_config import *
Dio("TIM3_CH2").set_state(True)
Dio("TIM3_CH2").set_value(1)
Dio("TIM3_CH2").set_value(0)

@Stanley Lin: It should be working. Can you confirm that the calibrated configuration is still valid? It's possible that a calibration can work once and then fail due to a change in ambient conditions. Also: The calibration was done with the same target I/O configuration (all management output except channel 0)?

Sorry for the late reply. The calibrated configuration is valid and all the IO are set to

C_MGMT_OUT

. The attached file is

gpio_config_io.py

for the gpio configuration.

I am regularly able to toggle all IOs (including

gpio[8]

) after successful calibration; there isn't anything special about channel 8.