add options to the SPI wrapper to mimic the IVVI driver

[peendebak]

Done

• make dac_delay an option

To be done:

• dac_step
• validator for range of values
• setting and getting in mV instead of V
• add locks for safe multi-threading

[eendebakpt]

@Rubenknex @mtiggelman Which of the options above do we want in the qcodes wrapper? The options are already implemented in

https://github.com/VandersypenQutech/Qcodes/blob/driver/spi/qcodes/instrument_drivers/QuTech/spiD5a.py

but I would rather combine the functionality there in this driver.

[eendebakpt]

Added a validator for the Parameter. The validator is not updated if the user changes the span in the underlying d5a module, but this is fine for most use cases.

[mtiggelman]

I'm not really familiar with or use Qcodes, so for me it doesn't matter. Think @Rubenknex should weigh in on this.

[Rubenknex]

@eendebakpt They all seem like reasonable functionality to add. But should we maybe merge the PR I made of the wrappers in the qcodes repository and continue development there like you mentioned in the email?

[eendebakpt]

@Rubenknex Developing either here or in the qcodes repo is fine with me. With git the difference is small anyway.

[Rubenknex]

@eendebakpt Let's move it to qcodes then, in order to use the SPI rack one then only has to pip install this package.

I will merge #6 to make this repository a package, and add your latest changes to the PR in qcodes.