Mercurial > hg > index.cgi

comparison docs/manual/x628.html @ 333:507f442dc71e

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Add support for 6800 compatibility instructions. The occasional program uses the 6800 compatibility instructions since they are actually specified by Motorola in at least some documentation. They advertised the 6809 as source compatible with the 6800. This mode is not enabled by default, however. It is my belief that receiving an error when using a non-6809 instruction is more useful since it is unlikely that much 6800 source code is being assembled for the 6809 these days. Nevertheless, the --6809compat option is present for just those purposes so one does not have to resort to using macros (which would work equally well in most cases).
author William Astle <lost@l-w.ca>
date Tue, 15 Apr 2014 10:57:34 -0600
parents
children 330a66a0f45a
comparison
equal deleted inserted replaced
332:26bfe8d557e2 333:507f442dc71e
1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd">
2 <HTML
3 ><HEAD
4 ><TITLE
5 >Assembler Modes and Pragmas</TITLE
6 ><META
7 NAME="GENERATOR"
8 CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK
9 REL="HOME"
10 TITLE="LW Tool Chain"
11 HREF="index.html"><LINK
12 REL="UP"
13 TITLE="LWASM"
14 HREF="c62.html"><LINK
15 REL="PREVIOUS"
16 TITLE="Object Files and Sections"
17 HREF="x564.html"><LINK
18 REL="NEXT"
19 TITLE="LWLINK"
20 HREF="c727.html"></HEAD
21 ><BODY
22 CLASS="SECTION"
23 BGCOLOR="#FFFFFF"
24 TEXT="#000000"
25 LINK="#0000FF"
26 VLINK="#840084"
27 ALINK="#0000FF"
28 ><DIV
29 CLASS="NAVHEADER"
30 ><TABLE
31 SUMMARY="Header navigation table"
32 WIDTH="100%"
33 BORDER="0"
34 CELLPADDING="0"
35 CELLSPACING="0"
36 ><TR
37 ><TH
38 COLSPAN="3"
39 ALIGN="center"
40 >LW Tool Chain</TH
41 ></TR
42 ><TR
43 ><TD
44 WIDTH="10%"
45 ALIGN="left"
46 VALIGN="bottom"
47 ><A
48 HREF="x564.html"
49 ACCESSKEY="P"
50 >Prev</A
51 ></TD
52 ><TD
53 WIDTH="80%"
54 ALIGN="center"
55 VALIGN="bottom"
56 >Chapter 3. LWASM</TD
57 ><TD
58 WIDTH="10%"
59 ALIGN="right"
60 VALIGN="bottom"
61 ><A
62 HREF="c727.html"
63 ACCESSKEY="N"
64 >Next</A
65 ></TD
66 ></TR
67 ></TABLE
68 ><HR
69 ALIGN="LEFT"
70 WIDTH="100%"></DIV
71 ><DIV
72 CLASS="SECTION"
73 ><H1
74 CLASS="SECTION"
75 ><A
76 NAME="AEN628"
77 >3.10. Assembler Modes and Pragmas</A
78 ></H1
79 ><P
80 >There are a number of options that affect the way assembly is performed.
81 Some of these options can only be specified on the command line because
82 they determine something absolute about the assembly process. These include
83 such things as the output target. Other things may be switchable during
84 the assembly process. These are known as pragmas and are, by definition,
85 not portable between assemblers.</P
86 ><P
87 >LWASM supports a number of pragmas that affect code generation or
88 otherwise affect the behaviour of the assembler. These may be specified by
89 way of a command line option or by assembler directives. The directives
90 are as follows.</P
91 ><P
92 ></P
93 ><DIV
94 CLASS="VARIABLELIST"
95 ><DL
96 ><DT
97 >PRAGMA <CODE
98 CLASS="PARAMETER"
99 >pragma[,...]</CODE
100 ></DT
101 ><DD
102 ><P
103 >Specifies that the assembler should bring into force all <CODE
104 CLASS="PARAMETER"
105 >pragma</CODE
106 >s
107 specified. Any unrecognized pragma will cause an assembly error. The new
108 pragmas will take effect immediately. This directive should be used when
109 the program will assemble incorrectly if the pragma is ignored or not supported.</P
110 ></DD
111 ><DT
112 >*PRAGMA <CODE
113 CLASS="PARAMETER"
114 >pragma[,...]</CODE
115 ></DT
116 ><DD
117 ><P
118 >This is identical to the PRAGMA directive except no error will occur with
119 unrecognized or unsupported pragmas. This directive, by virtue of starting
120 with a comment character, will also be ignored by assemblers that do not
121 support this directive. Use this variation if the pragma is not required
122 for correct functioning of the code.</P
123 ></DD
124 ><DT
125 >*PRAGMAPUSH <CODE
126 CLASS="PARAMETER"
127 >pragma[,...]</CODE
128 ></DT
129 ><DD
130 ><P
131 >This directive saves the current state of the specified pragma(s) for later retrieval. See discussion below for more information.</P
132 ><P
133 >This directive will not throw any errors for any reason.</P
134 ></DD
135 ><DT
136 >*PRAGMAPOP <CODE
137 CLASS="PARAMETER"
138 >pragma[,...]</CODE
139 ></DT
140 ><DD
141 ><P
142 >This directive restores the previously saved state of the specified pragma(s). See discussion below for more information.</P
143 ><P
144 >This directive will not throw any errors for any reason.</P
145 ></DD
146 ></DL
147 ></DIV
148 ><P
149 >Each pragma supported has a positive version and a negative version.
150 The positive version enables the pragma while the negative version disables
151 it. The negatitve version is simply the positive version with "no" prefixed
152 to it. For instance, "pragma" vs. "nopragma". When only one version is
153 listed below, its opposite can be obtained by prepending "no" if it is not
154 present or removing "no" from the beginning if it is present.</P
155 ><P
156 >Pragmas are not case sensitive.</P
157 ><P
158 ></P
159 ><DIV
160 CLASS="VARIABLELIST"
161 ><DL
162 ><DT
163 >6800compat</DT
164 ><DD
165 ><P
166 >When in force, this pragma enables recognition of various
167 compatibility instructions useful when assembling 6800 code. These
168 compatibility instructions are assembled into equivalent 6809 instructions.
169 This mode also includes several analogous instructions which are not
170 strictly 6800 instructions but allow the similar style to be applied to 6809
171 specific features.</P
172 ><P
173 >Technically, a compliant 6809 assembler must recognize these
174 instructions by default since Motorola advertised the 6809 as being source
175 compatible with the 6800. However, most source code does not require this
176 compatibility and LWASM itself did not support these instructions prior to
177 version 4.11 so this mode is disabled by default.</P
178 ></DD
179 ><DT
180 >index0tonone</DT
181 ><DD
182 ><P
183 >When in force, this pragma enables an optimization affecting indexed addressing
184 modes. When the offset expression in an indexed mode evaluates to zero but is
185 not explicity written as 0, this will replace the operand with the equivalent
186 no offset mode, thus creating slightly faster code. Because of the advantages
187 of this optimization, it is enabled by default.</P
188 ></DD
189 ><DT
190 >cescapes</DT
191 ><DD
192 ><P
193 >This pragma will cause strings in the FCC, FCS, and FCN pseudo operations to
194 have C-style escape sequences interpreted. The one departure from the official
195 spec is that unrecognized escape sequences will return either the character
196 immediately following the backslash or some undefined value. Do not rely
197 on the behaviour of undefined escape sequences.</P
198 ></DD
199 ><DT
200 >importundefexport</DT
201 ><DD
202 ><P
203 >This pragma is only valid for targets that support external references. When
204 in force, it will cause the EXPORT directive to act as IMPORT if the symbol
205 to be exported is not defined. This is provided for compatibility with the
206 output of gcc6809 and should not be used in hand written code. Because of
207 the confusion this pragma can cause, it is disabled by default.</P
208 ></DD
209 ><DT
210 >undefextern</DT
211 ><DD
212 ><P
213 >This pragma is only valid for targets that support external references. When in
214 force, if the assembler sees an undefined symbol on the second pass, it will
215 automatically define it as an external symbol. This automatic definition will
216 apply for the remainder of the assembly process, even if the pragma is
217 subsequently turned off. Because this behaviour would be potentially surprising,
218 this pragma defaults to off.</P
219 ><P
220 >The primary use for this pragma is for projects that share a large number of
221 symbols between source files. In such cases, it is impractical to enumerate
222 all the external references in every source file. This allows the assembler
223 and linker to do the heavy lifting while not preventing a particular source
224 module from defining a local symbol of the same name as an external symbol
225 if it does not need the external symbol. (This pragma will not cause an
226 automatic external definition if there is already a locally defined symbol.)</P
227 ><P
228 >This pragma will often be specified on the command line for large projects.
229 However, depending on the specific dynamics of the project, it may be sufficient
230 for one or two files to use this pragma internally.</P
231 ></DD
232 ><DT
233 >export</DT
234 ><DD
235 ><P
236 >This pragma causes all symbols to be added to the export list
237 automatically. This is useful when a large number of symbols need to be
238 exported but you do not wish to include an EXPORT directive for all of them.
239 This is often useful on the command line but might be useful even inline
240 with the PRAGMA directive if a large number of symbols in a row are to be
241 exported.</P
242 ></DD
243 ><DT
244 >dollarlocal</DT
245 ><DD
246 ><P
247 >When set, a "$" in a symbol makes it local. When not set, "$" does not
248 cause a symbol to be local. It is set by default except when using the OS9
249 target.</P
250 ></DD
251 ><DT
252 >dollarnotlocal</DT
253 ><DD
254 ><P
255 > This is the same as the "dollarlocal" pragma except its sense is
256 reversed. That is, "dollarlocal" and "nodollarnotlocal" are equivalent and
257 "nodollarlocal" and "dollarnotlocal" are equivalent. </P
258 ></DD
259 ><DT
260 >pcaspcr</DT
261 ><DD
262 ><P
263 > Normally, LWASM makes a distinction between PC and PCR in program
264 counter relative addressing. In particular, the use of PC means an absolute
265 offset from PC while PCR causes the assembler to calculate the offset to the
266 specified operand and use that as the offset from PC. By setting this
267 pragma, you can have PC treated the same as PCR. </P
268 ></DD
269 ><DT
270 >shadow</DT
271 ><DD
272 ><P
273 >When this pragma is in effect, it becomes possible to define a macro
274 that matches an internal operation code. Thus, it makes it possible to
275 redefine either CPU instructions or pseudo operations. Because this feature
276 is of dubious utility, it is disabled by default.</P
277 ></DD
278 ><DT
279 >nolist</DT
280 ><DD
281 ><P
282 >Lines where this pragma is in effect will not appear in the assembly
283 listing. Also, any symbols defined under this pragma will not show up in
284 the symbol list. This is most useful in include files to avoid spamming the
285 assembly listing with dozens, hundreds, or thousands of irrelevant
286 symbols.</P
287 ></DD
288 ><DT
289 >autobranchlength</DT
290 ><DD
291 ><P
292 >One of the perennial annoyances for 6809 programmers is that the
293 mneumonics for the short and long branch instructions are different (bxx vs.
294 lbxx), which is at odds with the rest of the instruction set. This pragma
295 is a solution to those annoying byte overflow errors that short branch
296 instructions tend to aquire.</P
297 ><P
298 >When this pragma is in effect, which is not the default, whenever any
299 relative branch instruction is used, its size will be automatically
300 determined based on the actual distance to the destination. In other words,
301 one can write code with long or short branches everywhere and the assembler
302 will choose a size for the branch.</P
303 ><P
304 >Also, while this pragma is in effect, the &#62; and &#60; symbols can be used
305 to force the branch size, analogous to their use for other instructions with
306 &#60; forcing 8 bit offsets and &#62; forcing 16 bit offets.</P
307 ><P
308 >Because this pragma leads to source that is incompatible with other
309 assemblers, it is strongly recommended that it be invoked using the PRAGMA
310 directive within the source code rather than on the command line or via the
311 *PRAGMA directive. This way, an error will be raised if someone tries to
312 assemble the code under a different assembler.</P
313 ></DD
314 ><DT
315 >nosymbolcase, symbolnocase</DT
316 ><DD
317 ><P
318 >Any symbol defined while this pragma is in force will be treated as
319 case insensitive, regardless whether the pragma is in force when the symbol
320 is referenced.</P
321 ><P
322 >It is important to note that this pragma will not work as expected in
323 all cases when using the object file assembly target. It is intended for
324 use only when the assembler will be producing the final binary.</P
325 ></DD
326 ><DT
327 >condundefzero</DT
328 ><DD
329 ><P
330 >This pragma will cause the assembler to change the way it handles
331 symbols in conditional expressions. Ordinarily, any symbol that is not
332 defined prior to the conditional will throw an undefined symbol error. With
333 this pragma in effect, symbols that are not yet defined at the point the
334 conditional is encountered will be treated as zero.</P
335 ><P
336 >This is not the default because it encourages poor code design. One
337 should use the "IFDEF" or "IFNDEF" conditionals to test for the presence of
338 a symbol.</P
339 ><P
340 >It is important to note that if a symbol is defined but it does not
341 yet evaluate to a constant value at the point where the conditional appears,
342 the assembler will still complain about a non constant condition.</P
343 ></DD
344 ></DL
345 ></DIV
346 ><P
347 >As a convenience, each input file has a pragma state stack. This
348 allows, through the use of *PRAGMAPUSH and *PRAGMAPOP, a file to change a
349 pragma state and then restore it to the precise state it had previously.
350 If, at the end of an input file, all pragma states have not been popped,
351 they will be removed from the stack. Thus, it is critical to employ
352 *PRAGMAPOP correctly. Because each input file has its own pragma stack,
353 using *PRAGMAPUSH in one file and *PRAGMAPOP in another file will not
354 work.</P
355 ><P
356 >Pragma stacks are more useful in include files, in particular in
357 conjunction with the nolist pragma. One can push the state of the nolist
358 pragma, engage the nolist pragma, and then pop the state of the nolist
359 pragma at the end of the include file. This will cause the entire include
360 file to operate under the nolist pragma. However, if the file is included
361 while nolist is already engaged, it will not undo that state.</P
362 ></DIV
363 ><DIV
364 CLASS="NAVFOOTER"
365 ><HR
366 ALIGN="LEFT"
367 WIDTH="100%"><TABLE
368 SUMMARY="Footer navigation table"
369 WIDTH="100%"
370 BORDER="0"
371 CELLPADDING="0"
372 CELLSPACING="0"
373 ><TR
374 ><TD
375 WIDTH="33%"
376 ALIGN="left"
377 VALIGN="top"
378 ><A
379 HREF="x564.html"
380 ACCESSKEY="P"
381 >Prev</A
382 ></TD
383 ><TD
384 WIDTH="34%"
385 ALIGN="center"
386 VALIGN="top"
387 ><A
388 HREF="index.html"
389 ACCESSKEY="H"
390 >Home</A
391 ></TD
392 ><TD
393 WIDTH="33%"
394 ALIGN="right"
395 VALIGN="top"
396 ><A
397 HREF="c727.html"
398 ACCESSKEY="N"
399 >Next</A
400 ></TD
401 ></TR
402 ><TR
403 ><TD
404 WIDTH="33%"
405 ALIGN="left"
406 VALIGN="top"
407 >Object Files and Sections</TD
408 ><TD
409 WIDTH="34%"
410 ALIGN="center"
411 VALIGN="top"
412 ><A
413 HREF="c62.html"
414 ACCESSKEY="U"
415 >Up</A
416 ></TD
417 ><TD
418 WIDTH="33%"
419 ALIGN="right"
420 VALIGN="top"
421 >LWLINK</TD
422 ></TR
423 ></TABLE
424 ></DIV
425 ></BODY
426 ></HTML
427 >