Mainly Tech projects on Python and Electronic Design Automation.

Tuesday, March 25, 2008

Writing a VCD to toggle-count generator in Python

I have an interesting problem at work which has been taxing me before
the Easter break. One of the less traditional ways forward is to write
a toggle count utility - something to take a simulation of a
hardware design and count which nets transition both to a zero and a
one in the simulation. For various reasons I could not get the design
to simulate in a modern version of a simulator with in-built toggle
counting without having to rebuild a C-based testbench for a later
version of an OS and a simulator that a major part of the TB is not
certified on.

I decided to spend my Easter Monday writing a VCD
to toggle-count

I started by searching my C: drive for a non-trivial vcd file and found
a ~200k/300 net sample generated from the Icarus Verilog program. I
then googled for the file format and found the IEEE 1394-2001 document
and went for that. I googled for ready-made utilities too and found an
interesting document on mining VCD files and parsing RTL to generate
all sorts of coverage metrics, but the VCD readers I found were in C
and, e.g. GTKWave
, and didn't seem to clarify how to write a vcd reader. (OK,
specifically - the liberal sprinkling of goto's in GTKWave sources put
me off, there - I've said it :-).

I moved on to read the IEEE spec, peruse my example vcd files, reject
writing an evcd (extended VCD), parser as I could
later extend a VCD parser, and I think the works simulator has enough
controls to tailor the VCD generated to be what I want.

The VCD files I will eventually have to work on may be a gigabyte in
size so I want to step through the file one token at a time gathering
stats as I go, and my reading of the VCD file format seemed to show
that that was possible, so the fist line of Python I wrote was this

175   tokeniser = (word for line in f for word in line.split() if word)

The above generator
, just gives successive words from the VCD file
without storing a huge chunk of the file in memory. tokeniser worked
originally with :

154 keyword2handler = {
155 # declaration_keyword ::=
156 "$comment": drop_declaration,
157 "$date": vcd_date,
158 "$enddefinitions": vcd_enddefinitions,
159 "$scope": vcd_scope,
160 "$timescale": vcd_timescale,
161 "$upscope": vcd_upscope,
162 "$var": vcd_var,
163 "$version": vcd_version,
164 # simulation_keyword ::=
165 "$dumpall": vcd_dumpall,
166 "$dumpoff": vcd_dumpoff,
167 "$dumpon": vcd_dumpon,
168 "$dumpvars": vcd_dumpvars,
169 "$end": vcd_end,
170 }

and the 'switch statement':

176   for count,token in enumerate(tokeniser):
181 keyword2handler[token](tokeniser, token)

... to form the guts of the program but when I had fleshed out all the
declaration keyword handlers beyond mere stubs, I decided to
add the second half of the parse routine as I realised that I would
skip all the simulation keywords and only needed to concentrate on the
first character of a token to determine what to do. This led to the
finished form of function vcd_toggle_count

I had thought that the rules for left-expanding a VCD value to a larger
word size might lead to a compact Python solution and i was pleased
with my result, which I tested in the Python interpreter as:

>>> for
number in "10 X10 ZX0 0X10".split():

extend = size-len(number)

print "%-4s -> %s" % (number,
('0' if number[0]=='1' else number[0])*extend + number)

-> 0010

-> XX10

-> ZZX0

0X10 -> 0X10

.This became:

 81       extend = stats.size - len(number)
82 if extend:
83 number = ('0' if number[0]=='1' else number[0])*extend + number

Well, enough prattling on about how I wrote the program, the full
source is below, and I'm off to work to to try it for real. It should
work, and since I have done no optimisations for speed as yet , I am
confident that I could get acceptable run-times out of its
variants to handle the gigabyte VCD file if I get one.

  1 #!python
2 '''
3 Extract toggle count from vcd file
5 Refer to IEEE standard 1364 2001
6 (
8 Author Donald 'Paddy' McCarthy (C) 24 March 2008
9 '''
11 from __future__ import with_statement
12 from itertools import dropwhile, takewhile, izip
13 from collections import defaultdict
14 from pprint import pprint as pp
16 vcdfile = r"C:\cygwin\home\HP DV8025EA\tmp\ivtest_v1.0\test_div16.vcd"
18 class VCD(object):
19 def __init__(self):
20 self.scope = []
21 self.idcode2references = defaultdict(list)
22 self.reference2idcode = dict()
23 self.enddefinitions = False
24 self.id2stats = dict() # Maps id to its accumulated statistics
25 def textstats(self):
26 total, updown, uponly, downonly = 0,0,0,0
27 out = []
28 for ref in sorted(self.reference2idcode.keys()):
29 id = self.reference2idcode[ref]
30 stats = self.id2stats[id]
31 if stats.size == 1:
32 total +=1
33 if stats.zero2one and stats.one2zero:
34 updown +=1
35 covered = 'PASS'
36 elif stats.zero2one:
37 uponly +=1
38 covered = 'FAIL0'
39 elif stats.one2zero:
40 downonly +=1
41 covered = 'FAIL1'
42 else:
43 covered = 'FAIL10'
44 out.append( " %-50s %s" % ( '"'+".".join(x[1] for x in ref)+'":', (covered, stats.zero2one, stats.one2zero)) )
45 else:
46 total += stats.size
47 for count, (one2zero, zero2one) in enumerate(izip(stats.one2zero, stats.zero2one)):
48 if zero2one and one2zero:
49 updown +=1
50 covered = 'PASS'
51 elif zero2one:
52 uponly +=1
53 covered = 'FAIL0'
54 elif stats.one2zero:
55 downonly +=1
56 covered = 'FAIL1'
57 else:
58 covered = 'FAIL10'
59 name = ".".join( x[1] for x in (ref+(('BIT:','<'+str(count)+'>'),)) )
60 out.append( " %-50s %s" % ( '"'+name+'":', (covered, zero2one, one2zero)) )
61 header = "# TOGGLE REPORT: %g %%, %i / %i covered. %i up-only, %i down-only." % (
62 updown/1.0/total*100, updown, total, uponly, downonly )
63 body = "toggle={\n" + "\n".join(out) + '\n }'
64 return header, body
66 def scaler_value_change(self, value, id):
67 if value in '01' :
68 stats = self.id2stats[id]
69 if not stats.value:
70 stats.value = value
71 elif stats.value != value:
72 stats.value = value
73 if value == '0':
74 stats.one2zero +=1
75 else:
76 stats.zero2one +=1
78 def vector_value_change(self, format, number, id):
79 if format == 'b':
80 stats = self.id2stats[id]
81 extend = stats.size - len(number)
82 if extend:
83 number = ('0' if number[0]=='1' else number[0])*extend + number
84 newdigit, newone2zero, newzero2one = [],[],[]
85 for digit, olddigit, one2zero, zero2one in izip(number, stats.value, stats.one2zero, stats.zero2one):
86 if digit in '01' and olddigit and olddigit != digit:
87 if digit == '0':
88 one2zero +=1
89 else:
90 zero2one +=1
91 elif digit not in '01':
92 digit = olddigit
93 newdigit.append(digit)
94 newone2zero.append(one2zero)
95 newzero2one.append(zero2one)
96 stats.value, stats.one2zero, stats.zero2one = newdigit, newone2zero, newzero2one
99 class IdStats(object):
100 def __init__(self, size):
101 size = int(size)
102 self.size = size
103 if size ==1:
104 self.value = ''
105 self.zero2one = 0
106 self.one2zero = 0
107 else:
108 # stats for each bit
109 self.value = ['' for x in range(size)]
110 self.zero2one = [0 for x in range(size)]
111 self.one2zero = [0 for x in range(size)]
112 def __repr__(self):
113 return "<IdStats: " + repr((self.size, self.value, self.zero2one, self.one2zero)) + ">"
116 vcd = VCD()
118 def parse_error(tokeniser, keyword):
119 raise "Don't understand keyword: " + keyword
121 def drop_declaration(tokeniser, keyword):
122 dropwhile(lambda x: x != "$end", tokeniser).next()
124 def save_declaration(tokeniser, keyword):
125 vcd.__setattr__(keyword.lstrip('$'),
126 " ".join( takewhile(lambda x: x != "$end", tokeniser)) )
127 vcd_date = save_declaration
128 vcd_timescale = save_declaration
129 vcd_version = save_declaration
131 def vcd_enddefinitions(tokeniser, keyword):
132 vcd.enddefinitions = True
133 drop_declaration(tokeniser, keyword)
134 def vcd_scope(tokeniser, keyword):
135 vcd.scope.append( tuple(takewhile(lambda x: x != "$end", tokeniser)))
136 def vcd_upscope(tokeniser, keyword):
137 vcd.scope.pop()
139 def vcd_var(tokeniser, keyword):
140 var_type, size, identifier_code, reference = tuple(takewhile(lambda x: x != "$end", tokeniser))
141 reference = vcd.scope + [('var', reference)]
142 vcd.idcode2references[identifier_code].append( (var_type, size, reference))
143 vcd.reference2idcode[tuple(reference)] = identifier_code
144 vcd.id2stats[identifier_code] = IdStats(size)
145 def vcd_dumpall(tokeniser, keyword): pass
146 def vcd_dumpoff(tokeniser, keyword): pass
147 def vcd_dumpon(tokeniser, keyword): pass
148 def vcd_dumpvars(tokeniser, keyword): pass
149 def vcd_end(tokeniser, keyword):
150 if not vcd.enddefinitions:
151 parse_error(tokeniser, keyword)
154 keyword2handler = {
155 # declaration_keyword ::=
156 "$comment": drop_declaration,
157 "$date": vcd_date,
158 "$enddefinitions": vcd_enddefinitions,
159 "$scope": vcd_scope,
160 "$timescale": vcd_timescale,
161 "$upscope": vcd_upscope,
162 "$var": vcd_var,
163 "$version": vcd_version,
164 # simulation_keyword ::=
165 "$dumpall": vcd_dumpall,
166 "$dumpoff": vcd_dumpoff,
167 "$dumpon": vcd_dumpon,
168 "$dumpvars": vcd_dumpvars,
169 "$end": vcd_end,
170 }
171 keyword2handler = defaultdict(parse_error, keyword2handler)
173 def vcd_toggle_count(vcdfile):
174 f = open(vcdfile)
175 tokeniser = (word for line in f for word in line.split() if word)
176 for count,token in enumerate(tokeniser):
177 if not vcd.enddefinitions:
178 # definition section
179 if token != '$var':
180 print token
181 keyword2handler[token](tokeniser, token)
182 else:
183 if count % 10000 == 0:
184 print count, "\r",
185 c, rest = token[0], token[1:]
186 if c == '$':
187 # skip $dump* tokens and $end tokens in sim section
188 continue
189 elif c == '#':
190 = rest
191 elif c in '01xXzZ':
192 vcd.scaler_value_change(value=c, id=rest)
193 elif c in 'bBrR':
194 vcd.vector_value_change(format=c.lower(), number=rest,
195 else:
196 raise "Don't understand: %s After %i words" % (token, count)
197 print count
198 f.close()
200 vcd_toggle_count(vcdfile)
201 header, body = vcd.textstats()
202 print '\n'+header+'\n\n'+body+'\n'

I'm back from work and the program worked with minor changes:
  1. I used the fileinput module to allow greater flexibility in specifying the input VCD file.
  2. Works, simulator had a slightly different interpretation of the spec around the definition of $var. (The spec needs to explicitely mark where spaces can/must occur).
  3. I missed adding commas to separate the output lines which should form a valid Python dict.
With an unchanged core algorithm the program churned through 200Mbytes of VCD file in 3 minutes. 2 gigs in 30 minutes is fine for me.

Sunday, March 23, 2008

Ain't Vista crap!

I went off to see the folks this weekend, one of which had a shiny new
Philips branded deskside PC that runs Vista. Being the member of the
family who is "in computers", I was asked to set up a few things for
them: (remove the login password; make frequently used tools easier to
find ...).

Now this was my first taste of Vista Premium and I was disappointed -
not with the display, that was a lovely 22 inch wide-screen LCD monitor
- It was the speed of the machine, or lack of it.

I should explain that I sit in front of a 1.8Gig Athlon based 17" HP
laptop at home, 1 Gig of ram, Windows XP, and Virgin broadband (cable,
4Megs). My machine is ~2 years old. The machine I was using with Vista
had 3 Gigs of Ram, and was a quad core Intel jobbie at 2.2Gigs. That is
three times the memory and four cores, each of which is faster than
mine. I expected Vista's response to be instant and it was not.

Some of the problems were to do with the broadband connection of the
Vista machine, which was Sky TV's broadband  deal (the one
that comes free with the TV subscription to try and combat Virgins
offerings),  there was a noticeable delay before pages started
to download; but a lot was to do with the machine itself:

  • Why did I have to wait for microsoft works wordprocessor to
    fire up?

  • Why did it take so long to boot-up from cold?

  • It just did not feel style="font-weight: bold; font-style: italic;">snappy!

I don't know if the recent Vista upgrade was installed, but this is a
very recent machine on very respectable hardware. Instead of being
green with envy I was shocked at how much of the hardware was wasted by
Vista (and to some extent Sky broadband).

(I should explain that the Vista machine is more than enough for what it will be used for and
my folks will be happy with it.)

This has got me worried. Multi-core is the solution for soaking up all
those extra trannies that Moore's law gives us over time, but Microsoft
Vista does not show the benefit.

Thinking about my next PC purchase, I have a family of two adults and
three children. If I were to buy a quad core laptop that I sat in front
of, I would want more than broadband traffic to go through my ethernet
cable. I would want it to be a transparent compute resource for several
thin-ish clients, maybe something like the Eee PC so the kids could
have a laptop they could use for school, but at home dock them to
 19" LCD screens and proper keyboards and Mice but more
importantly, they could use one of my quad cores transparently for
their compute intensive "Make a Video about Oxbow lakes" school assignments.
My normal TV's should have  just enough smarts to also act as
a (native), web browser and thin client, they could add the
functionality to my cable box. I want to be able to switch to BBC
Iplayer on the TV as well as any of the normal Cable TV offerings; or
select the news from, without buying a separate media-centre PC - I have four speedy cores just sitting in another room waiting to be shared!

Hopefully My future quad core machine would be better used if it was
packaged as a compute resource for the rest of my household items to

- Paddy.


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