Add finedelay test procedure

docs/how-to/finedelay-test.rst

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+Test the finedelay
+==================
+
+1. Plug two LVDSOUT pins to an oscilloscope and use rising edge of LVDSOUT1
+   as trigger.
+
+2. Enable CLOCK1, set its period to the minimum(0.016us) and use it as input for
+   LVDSOUT1 and LVDSOUT2.
+
+.. image:: ../images/finedelay_test_layout.png
+
+3. Set oct delay and fine delay to 0 in both LVDSOUTs.
+
+4. For LVDSOUT2, set oct delay from 1 to 7 and verify in the oscilloscope that
+   you get delays from 1ns to 7ns respectively, then set oct delay back to 0.
+
+5. Read initial one ns of LVDSOUT2 and use it as a reference to test fine delay.
+
+  5.1 Set fine delay to half of initial one ns and verify in the oscilloscope
+  that the delay is around 500ps.
+
+  5.2 Set fine delay to a quarter of initial one ns and verify in the
+  oscilloscope that the delay is around 250ps.
+
+  5.3 .... Repeat halving until you reach the limit of your oscilloscope ...
+
+6. Run a script_ that sweeps all fine delay values for each oct delay value and
+   observe how LVDSOUT2 gets delayed very smoothly.
+
+.. _script: https://raw.githubusercontent.com/PandABlocks/PandABlocks.github.io/refs/heads/main/scripts/finedelay-sweep.py

scripts/finedelay-sweep.py

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+#!/usr/bin/env python
+import argparse
+import socket
+import time
+
+
+def parse_args():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('host')
+    return parser.parse_args()
+
+
+def main():
+    args = parse_args()
+    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    s.connect((args.host, 8888))
+    for wide in range(8):
+        s.sendall(f'LVDSOUT2.OCT_DELAY={wide}\n'.encode())
+        assert s.recv(32) == b'OK\n'
+        time.sleep(0.5)
+
+    for wide in range(8):
+        s.sendall(f'LVDSOUT2.OCT_DELAY={wide}\n'.encode())
+        assert s.recv(32) == b'OK\n'
+        for fine in range(512):
+            s.sendall(f'LVDSOUT2.FINE_DELAY={fine}\n'.encode())
+            assert s.recv(32) == b'OK\n'
+            time.sleep(0.01)
+
+    time.sleep(1)
+    s.sendall('LVDSOUT2.OCT_DELAY=0\n'.encode())
+    s.sendall('LVDSOUT2.FINE_DELAY=0\n'.encode())
+    s.close()
+
+
+if __name__ == '__main__':
+    main()