From d992c7dd579170e226cfceabb652cdda6edb97b4 Mon Sep 17 00:00:00 2001
From: Olivier MATZ <zer0@droids-corp.org>
Date: Sun, 7 Mar 2010 21:00:38 +0100
Subject: [PATCH 1/1] save useful scripts

---
 .../microb2010/tests/static_beacon/cksum.py   | 51 +++++++++++++++++++
 .../microb2010/tests/static_beacon/coding.py  | 37 ++++++++++++++
 2 files changed, 88 insertions(+)
 create mode 100644 projects/microb2010/tests/static_beacon/cksum.py
 create mode 100644 projects/microb2010/tests/static_beacon/coding.py

diff --git a/projects/microb2010/tests/static_beacon/cksum.py b/projects/microb2010/tests/static_beacon/cksum.py
new file mode 100644
index 0000000..38d6634
--- /dev/null
+++ b/projects/microb2010/tests/static_beacon/cksum.py
@@ -0,0 +1,51 @@
+#!/usr/bin/python
+
+import random
+
+# val is 12 bits. Return the 16 bits value that includes the 4 bits
+# cksum in MSB.
+def do_cksum(val):
+    x = (val & 0xfff)
+    # add the three 4-bits blocks of x together
+    cksum = x & 0xf
+    x = x >> 4
+    cksum += x & 0xf
+    cksum = (cksum & 0xf) + ((cksum & 0xf0) >> 4)
+    x = x >> 4
+    cksum += x & 0xf
+    cksum = (cksum & 0xf) + ((cksum & 0xf0) >> 4)
+    cksum = (~cksum) & 0xf
+    return (cksum << 12) + (val & 0xfff)
+
+# val is 16 bits, including 4 bits-cksum in MSB, return 0xFFFF is cksum
+# is wrong, or the 12 bits value on success.
+def verify_cksum(val):
+    x = (val & 0xfff)
+    # add the four 4-bits blocks of val together
+    cksum = val & 0xf
+    val = val >> 4
+    cksum += val & 0xf
+    cksum = (cksum & 0xf) + ((cksum & 0xf0) >> 4)
+    val = val >> 4
+    cksum += val & 0xf
+    cksum = (cksum & 0xf) + ((cksum & 0xf0) >> 4)
+    val = val >> 4
+    cksum += val & 0xf
+    cksum = (cksum & 0xf) + ((cksum & 0xf0) >> 4)
+    if cksum == 0xf:
+        return x
+    return 0xffff # wrong value
+
+
+
+err = 0
+total = 0
+for i in range(200):
+    x = random.randint(0,(1<<12)-1)
+    y = do_cksum(x)
+    y = random.randint(0,(1<<16)-1)
+    z = verify_cksum(y)
+    if z == 0xffff:
+        err += 1
+    total += 1
+print "%d errors / %d"%(err, total)
diff --git a/projects/microb2010/tests/static_beacon/coding.py b/projects/microb2010/tests/static_beacon/coding.py
new file mode 100644
index 0000000..440fd3b
--- /dev/null
+++ b/projects/microb2010/tests/static_beacon/coding.py
@@ -0,0 +1,37 @@
+#!/usr/bin/python
+
+import sys, math
+
+RPS = 10.
+LASER_RADIUS = 25. # mm
+
+MIN = 200.
+MAX = 3500.
+NBITS = 9
+STEPS = (1 << 9)
+k = math.pow(MAX/MIN, 1./STEPS)
+
+# t is in us, result is 9 bits
+def time_to_frame(t):
+    # process angle from t
+    a = (t / (1000000./RPS)) * 2. * math.pi
+
+    # process d from a (between 20cm and 350cm)
+    d = LASER_RADIUS / math.sin(a/2)
+
+    frame = math.log(d/MIN)/math.log(k)
+    if frame >= 512:
+        frame = 511
+    else:
+        frame = int(frame)
+    print frame
+    return frame
+
+# frame is integer 9 bits, result is distance
+def frame_to_distance(frame):
+    d = MIN*(math.pow(k, frame))
+    print d
+    return d
+
+x = time_to_frame(float(sys.argv[1]))
+frame_to_distance(x)
-- 
2.20.1