Project

General

Profile

Template Description Language » History » Version 130

Andrei Tatarnikov, 02/27/2015 03:11 PM

1 5 Alexander Kamkin
h1. Template Description Language
2 4 Alexander Kamkin
3 97 Andrei Tatarnikov
_~By Artemiy Utekhin and Andrei Tatarnikov~_
4 1 Alexander Kamkin
5 21 Alexander Kamkin
*UNDER CONSTRUCTION*
6
7 6 Alexander Kamkin
{{toc}}
8
9 27 Andrei Tatarnikov
h2. Introduction
10
11 120 Andrei Tatarnikov
MicroTESK generates test programs on the basis of _test templates_ that provide an abstract description of scenarios to be reproduced by the generated programs. Test templates are created using the _test template description language_. It is a _Ruby_-based domain-specific language that provides facilities to describe test cases using symbolic names (that refer to a set of data satisfying certain conditions) instead of concrete input data and to manage the structure of the generated test programs. The language is implemented as a library that includes functionality for describing test templates and for further processing these test templates to produce a test program. MicroTESK uses the JRuby interpreter to process Ruby files. This allows Ruby libraries to interact with other components of MicroTESK written in Java.
12 1 Alexander Kamkin
13 45 Andrei Tatarnikov
h2. How It Works
14 1 Alexander Kamkin
15 121 Andrei Tatarnikov
A test template in Ruby describes a test program in terms of the model of the target microprocessor ISA. The structure of the test program is described using built-in features of Ruby (conditions, loops, etc.) and facilities provided by MicroTESK libraries (blocks that help organize instruction sequences). To provide access to elements of the model such as instructions and their addressing modes, corresponding Ruby methods are created at runtime on the basis on the meta-information provided by the model. The test template subsystem interacts with the model and the testing library of MicroTESK to create a symbolic test program, simulate it on the model and generate its textual representation. Generally speaking, processing of a test template is performed in the following steps:
16 46 Andrei Tatarnikov
17 101 Andrei Tatarnikov
* The model of the microprocessor is loaded;
18
* Runtime methods to access architecture-specific elements are created on the basis of the model''s meta-information;
19 121 Andrei Tatarnikov
* The code of the test template is executed to build the internal representation of the template described as a hierarchy of code blocks;
20
* Blocks are processed bottom-up to produce sequences of abstract instruction calls (at this step, their arguments can be described as a set of conditions instead of being assigned concrete values);
21 101 Andrei Tatarnikov
* A symbolic test program is built on the basis of the produced abstract instruction call sequences by applying corresponding algorithms to find values satisfying the specified conditions;
22
* The symbolic test program is simulated on the microprocessor model;
23
* The code of the test program is generated and saved to the output file.
24 1 Alexander Kamkin
25 3 Artemiy Utekhin
h2. Configuration
26 1 Alexander Kamkin
27 93 Andrei Tatarnikov
Global settings for the test template subsystem are specified in the <code>config.rb</code> file. These settings are related to the package structure and dependencies of the subsystem. They are predefined and rarely need to be modified. Also, there are local settings that control processing of individual test templates. They are specified as member variables of the <code>Template</code> class. Test templates can override them to customize the behavior of the subsystem. The settings will be discussed in more detail in the "Writing Test Templates" section.
28 1 Alexander Kamkin
29 35 Andrei Tatarnikov
h2. Running Test Program Generation
30 1 Alexander Kamkin
31 33 Andrei Tatarnikov
To start test program generation, a user needs to run the <code>generate.sh</code> script (Unix, Linux, OS X) or the <code>generate.bat</code> script (Windows) located in the <code>bin</code> folder. The script launches a Ruby program that processes the specified test template and produces a test program. The command to run the script has the following format: 
32 1 Alexander Kamkin
33
<pre>generate <model name> <template file.rb> [<output file.asm>]</pre>
34 7 Artemiy Utekhin
35 104 Andrei Tatarnikov
There are three parameters: (1) the name of the microprocessor model (generated by the [[Sim-nML Translator]] on the basis of Sim-nML specifications), (2) the name of the test template file to be processed and (3) the name of the test program file to be generated (optional, if it is skipped the program is printed to the console). For example, the following command processes the <code>example.rb</code> test template and saves the generated test program to the <code>test.asm</code> file:
36 7 Artemiy Utekhin
37 99 Andrei Tatarnikov
<pre>sh bin/generate.sh cpu arch/demo/cpu/templates/example.rb test.asm</pre>
38 1 Alexander Kamkin
39 56 Andrei Tatarnikov
h2. Writing Test Templates
40
41 57 Andrei Tatarnikov
h3. Test Template Structure
42
43 122 Andrei Tatarnikov
A test template is implemented as a class inherited from the <code>Template</code> library class that provides access to all features of the library. Information on the location of the <code>Template</code> class is stored in the <code>TEMPLATE</code> environment variable. So, the definition of a test template class looks like this:
44 57 Andrei Tatarnikov
45
<pre><code class="ruby">
46
require ENV[''TEMPLATE'']
47
48
class MyTemplate < Template</code></pre>
49 1 Alexander Kamkin
50 96 Andrei Tatarnikov
Test template classes should contain implementations of the following methods:
51 58 Andrei Tatarnikov
52 109 Andrei Tatarnikov
# <code>initialize</code> (optional) - specifies settings for the given test template;
53 105 Andrei Tatarnikov
# <code>pre</code> (optional) - specifies the initialization code for the test program;
54
# <code>post</code> (optional) - specifies the finalization code for the test program;
55
# <code>run</code> - specifies the main code of the test program (test cases).
56 58 Andrei Tatarnikov
57 63 Andrei Tatarnikov
The definitions of optional methods can be skipped. In this case, the default implementations provided by the parent class will be used. The default implementation of the <code>initialize</code> method initializes the settings with default values. The default implementations of the <code>pre</code> and <code>post</code> methods do nothing.
58
59 64 Andrei Tatarnikov
The full interface of a test template looks as follows:
60 60 Andrei Tatarnikov
61
<pre><code class="ruby">require ENV[''TEMPLATE'']
62
63
class MyTemplate < Template
64
65
  def initialize
66
    super
67
    # Initialize settings here 
68
  end
69
70
  def pre
71
    # Place your initialization code here
72
  end
73
74
  def post
75
    # Place your finalization code here
76
  end
77
78
  def run
79
    # Place your test problem description here
80
  end
81
82 61 Andrei Tatarnikov
end</code></pre>
83 57 Andrei Tatarnikov
84 65 Andrei Tatarnikov
h3. Reusing Test Templates
85
86 70 Andrei Tatarnikov
It is possible to reuse code of existing test templates in other test templates. To do this, you need to subclass the template you want to reuse instead of the <code>Template</code> class. For example, the <code>MyTemplate</code> class below reuses code from the <code>MyPrepost</code> class that provides initialization and finalization code for similar test templates.
87 68 Andrei Tatarnikov
88
<pre><code class="ruby">require ENV[''TEMPLATE'']
89
require_relative ''MyPrepost''
90
91 71 Andrei Tatarnikov
class MyTemplate < MyPrepost
92
93
  def run
94
  ... 
95
  end
96
97
end</code></pre>
98 68 Andrei Tatarnikov
99 74 Andrei Tatarnikov
h3. Test Template Settings
100
101 78 Andrei Tatarnikov
Test templates use the following settings:
102
103
# Use the standard output to print the generated test program (in addition to the output file);
104
# Enable logging information on the simulated instruction calls;
105
# Starting characters for single-line comments in the test program;
106 1 Alexander Kamkin
# Starting characters for multi-line comments in the test program;
107 107 Andrei Tatarnikov
# Terminating characters for multi-line comments in the test program;
108
# Seed for the randomizer.
109 78 Andrei Tatarnikov
110 79 Andrei Tatarnikov
Here is how these settings are initialized with default values in the <code>Template</code> class:
111 75 Andrei Tatarnikov
112 106 Andrei Tatarnikov
<pre><code class="ruby">
113
@use_stdout    = true
114
@log_execution = true
115
116 1 Alexander Kamkin
@sl_comment_starts_with = "// "
117
@ml_comment_starts_with = "/*"
118 106 Andrei Tatarnikov
@ml_comment_ends_with   = "*/"
119
120
@random_seed = 0
121
</code></pre>
122 72 Andrei Tatarnikov
123 107 Andrei Tatarnikov
The settings can be overridden in the <code>initialize</code> method of a test template. For example:
124 80 Andrei Tatarnikov
125
<pre><code class="ruby">class MyTemplate < Template
126
127
  def initialize
128
    super
129
    @sl_comment_starts_with = ";" 
130
    @ml_comment_starts_with = "/="
131
    @ml_comment_ends_with   = "=/" 
132
  end
133
  ...
134
end</code></pre>
135
136 111 Andrei Tatarnikov
h3. Data Definitions
137 1 Alexander Kamkin
138 119 Andrei Tatarnikov
Describing data requires the use of assembler-specific directives. Information of these directives in not included in ISA specifications and should be provided in test templates. It includes textual format of data directives and mappings between nML and assembler data types used by these directives. Configuration information on data directives is specified in the <code>data_config</code> block, which is usually placed in the <code>pre</code> method. Only one such block per template is allowed. Here is an example:
139 111 Andrei Tatarnikov
140 110 Andrei Tatarnikov
<pre><code class="ruby">
141
data_config(:text => ''.data'', :target => ''M'', :addressableSize => 8) {
142
  define_type :id => :byte, :text => ''.byte'', :type => type(''card'', 8)
143
  define_type :id => :half, :text => ''.half'', :type => type(''card'', 16)
144
  define_type :id => :word, :text => ''.word'', :type => type(''card'', 32)
145
146
  define_space :id => :space, :text => ''.space'', :fillWith => 0
147
  define_ascii_string :id => :ascii, :text => ''.ascii'', :zeroTerm => false
148
  define_ascii_string :id => :asciiz, :text => ''.asciiz'', :zeroTerm => true
149
}
150 1 Alexander Kamkin
</code></pre>
151 111 Andrei Tatarnikov
152 117 Andrei Tatarnikov
The block takes the following parameters (compulsory):
153 1 Alexander Kamkin
154 117 Andrei Tatarnikov
# _text_ - specifies the keyword that marks the beginning of the data section of the generated test program;
155
# _target_ - specifies the memory array defined in the nML specification to which data will be placed during simulation;
156
# _addressableSize_ - specifies the size (in bits) of addressable memory locations.
157
158 129 Andrei Tatarnikov
To set up particular directives, the language provides special methods that must be called inside the block. All the methods share two common parameters: _id_ and _text_. The first specifies the keyword to be used in a test template to address the directive and the second specifies how it will be printed in the test program. The current version of MicroTESK provides the following methods:
159 117 Andrei Tatarnikov
160 127 Andrei Tatarnikov
# _define_type_ - defines a directive to allocate memory for a data element of an nML data type specified by the _type_ parameter;
161
# _define_space_ - defines a directive to allocate uninitialized memory (one addressable location) filled with a default value specified by the _fillWith_ parameter;
162
# _define_ascii_string_ - defines a directive to allocate memory for an ASCII string terminated or not terminated with zero depending on the _zeroTerm_ parameter.
163 117 Andrei Tatarnikov
164 130 Andrei Tatarnikov
The above example defines the directives _byte_, _half_, _word_, _ascii_ (non-zero terminated string) and _asciiz_ (zero terminated string) that allocate memory in the memory array _M_ (specified in nML using the <code>mem</code> keyword). The size of an addressable memory location is 8 bits (or 1 byte).
165
166 117 Andrei Tatarnikov
After all data directives are configured, data can be defined using the <code>data</code> block:
167 110 Andrei Tatarnikov
168
<pre><code class="ruby">
169
data {
170
  label :data1
171
  word 1, 2, 3, 4
172
173
  label :data2
174
  half 0xDEAD, 0xBEEF
175
176
  label :hello
177
  ascii  ''Hello''
178
179
  label :world
180
  asciiz ''World''
181
182
  space 8
183
}
184
</code></pre>
185
186 1 Alexander Kamkin
TODO
187 110 Andrei Tatarnikov
188
-------------------
189 108 Andrei Tatarnikov
190 91 Andrei Tatarnikov
h3. Instruction Calls
191 1 Alexander Kamkin
192 86 Andrei Tatarnikov
The <code>pre</code>, <code>post</code> and <code>run</code> methods of a test template class contain specifications of instruction call sequences. Instruction calls are specified using the *_instruction_* and *_addressing mode_* abstractions. Instructions are self-explanatory, they simply represent target assembler instructions. Every instruction argument is a parameterized addressing mode that explains the meaning of the provided values. For example, an addressing mode can refer to a register, a memory location or hold an immediate value. In other words, an instruction call is an instruction that uses appropriate addressing modes initialized with appropriate values. The format of an instruction call description looks like this:
193 85 Andrei Tatarnikov
194 88 Andrei Tatarnikov
<pre><code class="ruby">instruction addr_mode1(:arg1_1 => value1_1, :arg1_2 => value1_2, ...), addr_mode2(:arg2_1 => value2_1, ...), ...</code></pre>
195 1 Alexander Kamkin
196 89 Andrei Tatarnikov
This format implies that addressing modes are parameterized with hash tables where they key is in the name of the addressing mode parameter and the value is the value to be assigned to this parameter. Also, there is a shorter format based on methods with a variable number of arguments. In this case, values are expected to come in the same order as corresponding parameter definitions. The shorter format looks like this:
197
198
<pre><code class="ruby">instruction addr_mode1(value1_1, value1_2, ...), addr_mode2(value2_1, ...), ...</code></pre>
199
200 90 Andrei Tatarnikov
The code below demonstrates both approaches:
201
202
<pre><code class="ruby">
203
mov reg(:i => 0), imm(:i => 0xFF) # The use of hash maps
204
mov reg(0), imm(0xFF)             # The use of variable numbers of arguments
205 1 Alexander Kamkin
</code></pre>
206 91 Andrei Tatarnikov
207
h3. Instruction Call Blocks
208
209
210 90 Andrei Tatarnikov
211 20 Alexander Kamkin
h2. *TODO: REWRITE*
212 1 Alexander Kamkin
213 20 Alexander Kamkin
h3. Basic features
214 1 Alexander Kamkin
215 11 Andrei Tatarnikov
The two core abstractions used by MicroTESK parser/simulator and Ruby-TDL are an *instruction* and an *addressing mode*. An instruction is rather self-explanatory, it simply represents a target assembler instruction. Every argument of an instruction is a parametrized *addressing mode* that explains the meaning of the provided values to the simulator. The mode could point to the registers, for instance, or to a specific memory location. It can also denote an immediate value - e.g. a simple integer or a string. Thus, a basic template is effectively a sequence of instructions with parametrized addressing modes as their arguments.
216 1 Alexander Kamkin
217 11 Andrei Tatarnikov
Each template is a class that inherits a basic Template class that provides most of the core Ruby-TDL functionality. So, to write a template you need to subclass Template first:
218 1 Alexander Kamkin
219 20 Alexander Kamkin
<pre><code class="ruby">require_relative "_path-to-the-rubymt-library_/mtruby"
220 1 Alexander Kamkin
221 3 Artemiy Utekhin
class MyTemplate < Template</code></pre>
222 1 Alexander Kamkin
223 10 Andrei Tatarnikov
While processing a template Ruby-TDL calls its %pre%, %run% and %post% methods, loosely meaning the pre-conditions, the main body and the post-conditions. The %pre% method is mostly useful for setup common to many templates, the %post% method will be more important once sequential testing is introduced. Most of the template code is supposed to be in the %run% method. Thus, a template needs to override one or more of these methods, most commonly %run%.
224 1 Alexander Kamkin
225 3 Artemiy Utekhin
To get %pre% and %post% over with, the most common usage of these is to make a special non-executable class and then subclass it with the actual templates:
226
227
<pre><code class="ruby">require_relative "_path-to-the-rubymt-library_/mtruby"
228
229
class MyPrepost < Template
230 1 Alexander Kamkin
  def initialize
231 3 Artemiy Utekhin
    super
232
    @is_executable = no
233
  end
234 1 Alexander Kamkin
235 3 Artemiy Utekhin
  def pre
236
    # Your ''startup'' code goes here
237
  end
238 9 Andrei Tatarnikov
239 1 Alexander Kamkin
  def post
240 11 Andrei Tatarnikov
    # Your ''cleanup'' code goes here
241 1 Alexander Kamkin
  end
242 3 Artemiy Utekhin
end</code></pre>
243
244
<pre><code class="ruby">require_relative "_path-to-the-rubymt-library_/mtruby"
245
246
class MyTemplate < MyPrepost
247
  def initialize
248
    super
249
    @is_executable = yes
250
  end
251 11 Andrei Tatarnikov
  
252 1 Alexander Kamkin
  def run
253 3 Artemiy Utekhin
    # Your template code goes here
254 1 Alexander Kamkin
  end
255 16 Andrei Tatarnikov
end</code></pre>
256 1 Alexander Kamkin
257 3 Artemiy Utekhin
These methods essentially contain the instructions. The general instruction format is slightly more intimidating than the native assembler and looks like this:
258 1 Alexander Kamkin
259 16 Andrei Tatarnikov
<pre><code class="ruby">instruction_name addr_mode1(:arg1_1 => value, :arg1_2 => value, ...), addr_mode2(:arg2_1 => value, ...), ...</code></pre>
260 1 Alexander Kamkin
261 3 Artemiy Utekhin
So, for instance, if the simulator has an ADD(MEM(i), MEM(i)|IMM(i)) instruction, it would look like:
262 1 Alexander Kamkin
263 16 Andrei Tatarnikov
<pre><code class="ruby">add mem(:i => 42), imm(:i => 128)</code></pre>
264 3 Artemiy Utekhin
265 8 Artemiy Utekhin
Thankfully, there are shortcuts. If there''s only one argument expected in the addressing mode, you can simply write its value and never have to worry about the argument name. And, by convention, the immediate values are always denoted in the simulator as the IMM addressing mode, so the template parser automatically accepts numbers and strings as such. Thus, in this case, the instruction can be simplified to:
266
267 16 Andrei Tatarnikov
<pre><code class="ruby">add mem(42), 128</code></pre>
268 8 Artemiy Utekhin
269 3 Artemiy Utekhin
As a matter of fact, if you''re sure about the order of addressing mode arguments, you can omit the names altogether and simply provide the values:
270
271
<pre><code class="ruby">instruction_name addr_mode1(value1, value2, ...) ...</code></pre>
272
273
If the name of the instruction conflicts with an already existing Ruby method, the instruction will be available with an %op_% prefix before its name.
274
275
h3. Test situations
276
277
_This section is to be taken with a grain of salt because the logic and the interface behind the situations is not yet finalized and mostly missing from the templates and shouldn''t be used yet_
278
279 17 Andrei Tatarnikov
_Big TODO: define what is a test situation_
280 3 Artemiy Utekhin
281
To denote a test situation, add a Ruby block that describes situations to an instruction, this will loosely look like this (likely similar to the way the addressing modes are denoted):
282
283
<pre><code class="ruby">sub mem(42), mem(21) do overflow(:op1 => 123, :op2 => 456) end</code></pre>
284
285 12 Andrei Tatarnikov
h3. Instruction blocks
286 3 Artemiy Utekhin
287
Sometimes a certain test situation should influence more than just one instruction. In that case, you can pass the instructions in an atomic block that can optionally accept a Proc of situations as its argument (because Ruby doesn''t want to be nice and allow multiple blocks for a method, and passing a Hash of Proc can hardly be called comfortable).
288
289
<pre><code class="ruby">p = lambda { overflow(:op1 => 123, :op2 => 456) }
290
291 12 Andrei Tatarnikov
atomic p {
292 3 Artemiy Utekhin
  mov mem(25), mem(26)
293 25 Andrei Tatarnikov
  add mem(27), 28
294 3 Artemiy Utekhin
  sub mem(29), 30
295 24 Andrei Tatarnikov
}</code></pre>
296
297
h3. Groups and random selections _(N.B. REMOVED in r1923. The implementation does not work in the current build and, therefore, was removed. The described features must be reviewed and reimplemented if required.)_
298
299
From source code comments:
300
301
<pre>
302
# VERY UNTESTED leftovers from the previous version ("V2", this is V3)
303
# Should work with the applied fixes but I''d be very careful to use these
304
305 3 Artemiy Utekhin
# As things stand this is just a little discrete probability utility that
306
# may or may not find its way into the potential ruby part of the test engine
307
</pre>
308
309 17 Andrei Tatarnikov
There are certain ways to group together or randomize addressing modes and instructions.
310 3 Artemiy Utekhin
311
To group several addressing modes together (this only works if they have similar arguments) create a mode group like this:
312
313 17 Andrei Tatarnikov
<pre><code class="ruby">mode_group "my_group" [:mem, :imm]</code></pre>
314 3 Artemiy Utekhin
315
You can also set weights to each of the modes in the group like this:
316
317 17 Andrei Tatarnikov
<pre><code class="ruby">mode_group "my_group" {:mem => 1.5, :imm => 2.5}</code></pre>
318 3 Artemiy Utekhin
319
The name of the group is converted into a method in the Template class. To select a random mode from a group, use %sample% on this generated method:
320
321
<pre><code class="ruby">add mem(42), my_group.sample(21)</code></pre>
322
323 17 Andrei Tatarnikov
_TODO: sampling already parametrized modes_
324 3 Artemiy Utekhin
325 17 Andrei Tatarnikov
The first method of grouping instructions works in a similar manner with the same restrictions on arguments:
326 3 Artemiy Utekhin
327 17 Andrei Tatarnikov
<pre><code class="ruby">group "i_group" [:add, :sub]</code></pre>
328 3 Artemiy Utekhin
329
<pre><code class="ruby">group "i_group" {:add => 0.3, :sub => 0.7]</code></pre>
330
331 17 Andrei Tatarnikov
<pre><code class="ruby">i_group.sample mem(42), 21</code></pre>
332 3 Artemiy Utekhin
333
You can also run all of the instructions in a group at once by using the %all% method:
334
335 17 Andrei Tatarnikov
<pre><code class="ruby">i_group.all mem(42), 21</code></pre>
336 3 Artemiy Utekhin
337
The second one allows you to create a normal block of instructions, setting their arguments separately. 
338
339 17 Andrei Tatarnikov
<pre><code class="ruby">block_group "b_group" do
340 3 Artemiy Utekhin
  mov mem(25), mem(26)
341
  add mem(27), 28
342
  sub mem(29), 30
343 17 Andrei Tatarnikov
end</code></pre>
344 3 Artemiy Utekhin
345
In this case to set weights you should call a %prob% method before every instruction:
346
347
<pre><code class="ruby">block_group "b_group" do
348
  prob 0.1
349
  mov mem(25), mem(26)
350 17 Andrei Tatarnikov
  prob 0.7
351 3 Artemiy Utekhin
  add mem(27), 28
352
  prob 0.4
353
  sub mem(29), 30
354 18 Andrei Tatarnikov
end</code></pre>
355
356 3 Artemiy Utekhin
The usage is almost identical, but without providing the arguments as they are already set:
357
358
<pre><code class="ruby">b_group.sample
359
b_group.all</code></pre>
360
361
_Not sure how does it work inside atomics when the group is defined outside, needs more consideration_
362 8 Artemiy Utekhin
363
_TODO: Permutations_
364
365
Any normal Ruby code is allowed inside the blocks as well as the %run%-type methods, letting you write more complex or inter-dependent templates.
366
367 18 Andrei Tatarnikov
h3. TODO: Labels
368 8 Artemiy Utekhin
369
To set a label write:
370
371 18 Andrei Tatarnikov
<pre><code class="ruby">label :label_name</code></pre>
372 8 Artemiy Utekhin
373
To use a label in an instruction that accepts one (under the hood it''s just a simple immediate #IMM value - just not a pre-defined one until it''s actually defined):
374
375
<pre><code class="ruby">b greaterThan, :label_name</code></pre>
376
377 15 Andrei Tatarnikov
h3. TODO: Debug
378 8 Artemiy Utekhin
379
To get a value from registers use:
380
381
<pre><code class="ruby">get_reg_value("register_name", index)</code></pre>
382
383 15 Andrei Tatarnikov
Right now the pre-processing and the execution of instructions are separated due to ambiguous logic regarding labels and various blocks and atomics. This may be changed later, so these special debugging blocks might become unnecessary. By default what''s written in the template is run during pre-processing so you have to use special blocks if you want to run some Ruby code during the execution stage, most likely some debugging.
384 8 Artemiy Utekhin
385 15 Andrei Tatarnikov
To print some debug in the console during the execution of the instructions use the exec_debug block:
386 8 Artemiy Utekhin
387
<pre><code class="ruby">exec_debug {
388
  puts "R0: " + get_reg_value("GPR", 0).to_s + ", R1: " + get_reg_value("GPR", 1).to_s# + ", label code: " + self.send("cycle" + ind.to_s).to_s
389 14 Andrei Tatarnikov
}</code></pre>
390 8 Artemiy Utekhin
391 13 Andrei Tatarnikov
To save something that depends on the current state of the simulator to the resulting assembler code use exec_output that should return a string:
392 1 Alexander Kamkin
393
<pre><code class="ruby">exec_output {
394
  "// The result should be " + self.get_reg_value("GPR", 0).to_s
395
}</code></pre>