Fix QDac for qcodes v0.8.0: inconsistent values for vrange

[Dominik-Vogel]

This addresses an issues that came to light with the improvement of the cache in qcodes v0.8.0. The 'vrange' parameter was used inconsistently. (So was 'irange')

A lot of refactoring was necessary in order to find the bug, but it is a good time to do the refactoring since the new driver version needs to be tested on a real device anyway.

Ready for review, but not merging, since the hardware tests are missing.

[astafan8]

Great work cleaning up this :)

[astafan8]

isn't is possible to call self._set_vrange(chan, v_range) here instead of self._update_v_validator(channel, v_range) and channel.v.cache(v * 0.1 if v_range else v)? i'm especially worried about duplicating the v * 0.1 part of the logic.

[Dominik-Vogel]

You are speaking from my heart. I really wanted to refactor this and already started doing it. But I had to undo the refactoring. Now I have been thinking about it for a while and defined the right vocabulary, writing a github comment, almost in love-letter format, to you. After that I realized a good way of refactoring and implemented it ;-).

[astafan8]

great :)

[codecov]

Codecov Report

Merging #1844 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1844      +/-   ##
==========================================
- Coverage   70.37%   70.37%   -0.01%     
==========================================
  Files         152      152              
  Lines       18847    18847              
==========================================
- Hits        13264    13263       -1     
- Misses       5583     5584       +1

[Dominik-Vogel]

This code has now been tested including the actual voltage output:

ch = qdac.ch41

def assert_equal(v):
    assert np.isclose(ch.v.cache(), v, rtol=1e-2)
    assert np.isclose(ch.v(), v, rtol=1e-2)
    assert np.isclose(ch.v(), dmm.volt(), rtol=1e-2)

ch.vrange(0)
ch.v(1)
assert_equal(1)
ch.vrange(1)
assert_equal(0.1)
ch.vrange(0)
assert_equal(1)
ch.vrange(0)
ch.v(0.5)
assert_equal(0.5)
ch.vrange(1)
assert_equal(0.05)