i2c-plot.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

'''
i2c-plot.py

Script for plotting data streams from I2C. Needs file for each SDA and SCL capture in a TSV format with the first column for time (microseconds) and second being state (1 or 0). These are generated by the gpio-dump.py

The script uses the gpio-dump-template.svg as a template and adds elements to it.
The SCL is depicted as a square wave and high periods on the SDA are depicted as blue blocks.

Dependencies:
  python-bs4
  python-lxml

ToDo:
-set image width to match plot.
-make a I2C reading library which automatically assigns labels.

Changelog:
2015-12-25: Created (Devon Fyson)

'''

from bs4 import BeautifulSoup  #http://www.crummy.com/software/BeautifulSoup/bs4/doc/

#user vars
offset=20 #pixels to offset first transition.
#scaleAuto=False #automatically scale time.
timeScale=10 #microseconds per pixel.
sdaLog="gpio-dump_sda.log" #file with i2c sda data.
sclLog="gpio-dump_scl.log" #file with i2c scl data
outputFile="gpio-dump.svg"
limit=100 #max number of state changes to process incase things get crazy.

#internal vars
sda1=0 #time of first SDA interupt.
scl1=0 #time of first SCL interupt.
logOffset=0 #offset in logfile.


f1 = open(sdaLog, 'r')
f2 = open(sclLog, 'r')
sda1 = int(f1.readline().split("\t",1)[0]) #get the first timestamp
scl1 = int(f2.readline().split("\t",1)[0])
f1.seek(0)
f2.seek(0)

# load the SVG template.
with open ("gpio-dump-template.svg", "r") as f:
	data=f.read()#.replace('\n', '')
soup = BeautifulSoup(data, "xml")
sdaXML=soup.find(id="sda")
sclXML=soup.find(id="scl")

# get the time of the first state change for either SDA or SCL (SDA should usually be first)
if scl1 <= sda1:
	logOffset=scl1
else:
	logOffset=sda1

# parse SDA data to SVG.
t2 = s2 = i = 0
for line in f1:
	if line.strip():
		l = line.split("\t",2) #get time and state
	t1 = int(l[0])-logOffset+float(offset*timeScale)
	s1 = int(l[1])

	if s1 == 0:
		tag = soup.new_tag("rect")
		tag['y'] = "-15"
		tag['x'] = str(float(t2/timeScale))
		tag['height'] = "30"
		tag['width'] = str(float((t1-t2)/timeScale))
		tag['class'] = "sda"
		sdaXML.append(tag)
	if (s1 == s2) & (t2 > 0): #two consecutive interrupts shouldn't have same value. But dont check fisrt.
		print("Warning: two consecutive states are the same for SDA at "+str(t2+logOffset-float(offset*timeScale)))
	t2 = t1
	s2 = s1
	i = i+1
	if i >= limit:
		break

# parse SCL data to SVG.
t2 = s2 = i = 0
for line in f2:
	if line.strip():
		l = line.split("\t",2) #get time and state
	t1 = int(l[0])-logOffset+float(offset*timeScale)
	s1 = int(l[1])
	#vertical line denoting a new clock sequence (transition from 1 to 0)
	tag = soup.new_tag("path")
	tag['d'] = "m "+str(float(t1/timeScale))+",-15 0,30"
	tag['class'] = "scl"+str(s1)
	sclXML.append(tag)
	#put in connecting lines between adjacent vertical lines to make it look more like a square wave clock signal.
	tag = soup.new_tag("path")
	if (s1 == 0):
		tag['d'] = "m "+str(float(t2/timeScale))+",-15 "+str(float((t1-t2)/timeScale))+",0"
	else:
		tag['d'] = "m "+str(float(t2/timeScale))+",15 "+str(float((t1-t2)/timeScale))+",0"
	tag['class'] = "scl1"
	sclXML.append(tag)
	if (s1 == s2) & (t2 > 0): #two consecutive interrupts shouldn't have same value. But dont check fisrt.
		print("Warning: two consecutive states are the same for SCL at "+str(t2+logOffset-float(offset*timeScale)))
	t2 = t1
	s2 = s1
	i = i+1
	if i >= limit:
		break

f1.close()
f2.close()

#write the SVG to file.
with open(outputFile, 'w') as f:
	f.write(soup.prettify())