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toolchain-gcc-arm-embedded/share/doc/gcc-arm-none-eabi/html/gcc/AVR-Options.html

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  70. <a name="AVR-Options"></a>

  71. <div class="header">

  72. <p>

  73. Next: <a href="Blackfin-Options.html#Blackfin-Options" accesskey="n" rel="next">Blackfin Options</a>, Previous: <a href="ARM-Options.html#ARM-Options" accesskey="p" rel="prev">ARM Options</a>, Up: <a href="Submodel-Options.html#Submodel-Options" accesskey="u" rel="up">Submodel Options</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>

  74. </div>

  75. <hr>

  76. <a name="AVR-Options-1"></a>

  77. <h4 class="subsection">3.19.6 AVR Options</h4>

  78. <a name="index-AVR-Options"></a>

  79. 

  80. <p>These options are defined for AVR implementations:

  81. </p>

  82. <dl compact="compact">

  83. <dt><code>-mmcu=<var>mcu</var></code></dt>

  84. <dd><a name="index-mmcu"></a>

  85. <p>Specify Atmel AVR instruction set architectures (ISA) or MCU type.

  86. </p>

  87. <p>The default for this option is&nbsp;&lsquo;<samp>avr2</samp>&rsquo;.

  88. </p>

  89. <p>GCC supports the following AVR devices and ISAs:

  90. </p>

  91. 

  92. 

  93. 

  94. <dl compact="compact">

  95. <dt><code>avr2</code></dt>

  96. <dd><p>&ldquo;Classic&rdquo; devices with up to 8&nbsp;KiB of program memory.

  97. <br><var>mcu</var>&nbsp;= <code>attiny22</code>, <code>attiny26</code>, <code>at90s2313</code>, <code>at90s2323</code>, <code>at90s2333</code>, <code>at90s2343</code>, <code>at90s4414</code>, <code>at90s4433</code>, <code>at90s4434</code>, <code>at90c8534</code>, <code>at90s8515</code>, <code>at90s8535</code>.

  98. </p>

  99. </dd>

  100. <dt><code>avr25</code></dt>

  101. <dd><p>&ldquo;Classic&rdquo; devices with up to 8&nbsp;KiB of program memory and with the <code>MOVW</code> instruction.

  102. <br><var>mcu</var>&nbsp;= <code>attiny13</code>, <code>attiny13a</code>, <code>attiny24</code>, <code>attiny24a</code>, <code>attiny25</code>, <code>attiny261</code>, <code>attiny261a</code>, <code>attiny2313</code>, <code>attiny2313a</code>, <code>attiny43u</code>, <code>attiny44</code>, <code>attiny44a</code>, <code>attiny45</code>, <code>attiny48</code>, <code>attiny441</code>, <code>attiny461</code>, <code>attiny461a</code>, <code>attiny4313</code>, <code>attiny84</code>, <code>attiny84a</code>, <code>attiny85</code>, <code>attiny87</code>, <code>attiny88</code>, <code>attiny828</code>, <code>attiny841</code>, <code>attiny861</code>, <code>attiny861a</code>, <code>ata5272</code>, <code>ata6616c</code>, <code>at86rf401</code>.

  103. </p>

  104. </dd>

  105. <dt><code>avr3</code></dt>

  106. <dd><p>&ldquo;Classic&rdquo; devices with 16&nbsp;KiB up to 64&nbsp;KiB of program memory.

  107. <br><var>mcu</var>&nbsp;= <code>at76c711</code>, <code>at43usb355</code>.

  108. </p>

  109. </dd>

  110. <dt><code>avr31</code></dt>

  111. <dd><p>&ldquo;Classic&rdquo; devices with 128&nbsp;KiB of program memory.

  112. <br><var>mcu</var>&nbsp;= <code>atmega103</code>, <code>at43usb320</code>.

  113. </p>

  114. </dd>

  115. <dt><code>avr35</code></dt>

  116. <dd><p>&ldquo;Classic&rdquo; devices with 16&nbsp;KiB up to 64&nbsp;KiB of program memory and with the <code>MOVW</code> instruction.

  117. <br><var>mcu</var>&nbsp;= <code>attiny167</code>, <code>attiny1634</code>, <code>atmega8u2</code>, <code>atmega16u2</code>, <code>atmega32u2</code>, <code>ata5505</code>, <code>ata6617c</code>, <code>ata664251</code>, <code>at90usb82</code>, <code>at90usb162</code>.

  118. </p>

  119. </dd>

  120. <dt><code>avr4</code></dt>

  121. <dd><p>&ldquo;Enhanced&rdquo; devices with up to 8&nbsp;KiB of program memory.

  122. <br><var>mcu</var>&nbsp;= <code>atmega48</code>, <code>atmega48a</code>, <code>atmega48p</code>, <code>atmega48pa</code>, <code>atmega48pb</code>, <code>atmega8</code>, <code>atmega8a</code>, <code>atmega8hva</code>, <code>atmega88</code>, <code>atmega88a</code>, <code>atmega88p</code>, <code>atmega88pa</code>, <code>atmega88pb</code>, <code>atmega8515</code>, <code>atmega8535</code>, <code>ata6285</code>, <code>ata6286</code>, <code>ata6289</code>, <code>ata6612c</code>, <code>at90pwm1</code>, <code>at90pwm2</code>, <code>at90pwm2b</code>, <code>at90pwm3</code>, <code>at90pwm3b</code>, <code>at90pwm81</code>.

  123. </p>

  124. </dd>

  125. <dt><code>avr5</code></dt>

  126. <dd><p>&ldquo;Enhanced&rdquo; devices with 16&nbsp;KiB up to 64&nbsp;KiB of program memory.

  127. <br><var>mcu</var>&nbsp;= <code>atmega16</code>, <code>atmega16a</code>, <code>atmega16hva</code>, <code>atmega16hva2</code>, <code>atmega16hvb</code>, <code>atmega16hvbrevb</code>, <code>atmega16m1</code>, <code>atmega16u4</code>, <code>atmega161</code>, <code>atmega162</code>, <code>atmega163</code>, <code>atmega164a</code>, <code>atmega164p</code>, <code>atmega164pa</code>, <code>atmega165</code>, <code>atmega165a</code>, <code>atmega165p</code>, <code>atmega165pa</code>, <code>atmega168</code>, <code>atmega168a</code>, <code>atmega168p</code>, <code>atmega168pa</code>, <code>atmega168pb</code>, <code>atmega169</code>, <code>atmega169a</code>, <code>atmega169p</code>, <code>atmega169pa</code>, <code>atmega32</code>, <code>atmega32a</code>, <code>atmega32c1</code>, <code>atmega32hvb</code>, <code>atmega32hvbrevb</code>, <code>atmega32m1</code>, <code>atmega32u4</code>, <code>atmega32u6</code>, <code>atmega323</code>, <code>atmega324a</code>, <code>atmega324p</code>, <code>atmega324pa</code>, <code>atmega325</code>, <code>atmega325a</code>, <code>atmega325p</code>, <code>atmega325pa</code>, <code>atmega328</code>, <code>atmega328p</code>, <code>atmega328pb</code>, <code>atmega329</code>, <code>atmega329a</code>, <code>atmega329p</code>, <code>atmega329pa</code>, <code>atmega3250</code>, <code>atmega3250a</code>, <code>atmega3250p</code>, <code>atmega3250pa</code>, <code>atmega3290</code>, <code>atmega3290a</code>, <code>atmega3290p</code>, <code>atmega3290pa</code>, <code>atmega406</code>, <code>atmega64</code>, <code>atmega64a</code>, <code>atmega64c1</code>, <code>atmega64hve</code>, <code>atmega64hve2</code>, <code>atmega64m1</code>, <code>atmega64rfr2</code>, <code>atmega640</code>, <code>atmega644</code>, <code>atmega644a</code>, <code>atmega644p</code>, <code>atmega644pa</code>, <code>atmega644rfr2</code>, <code>atmega645</code>, <code>atmega645a</code>, <code>atmega645p</code>, <code>atmega649</code>, <code>atmega649a</code>, <code>atmega649p</code>, <code>atmega6450</code>, <code>atmega6450a</code>, <code>atmega6450p</code>, <code>atmega6490</code>, <code>atmega6490a</code>, <code>atmega6490p</code>, <code>ata5795</code>, <code>ata5790</code>, <code>ata5790n</code>, <code>ata5791</code>, <code>ata6613c</code>, <code>ata6614q</code>, <code>ata5782</code>, <code>ata5831</code>, <code>ata8210</code>, <code>ata8510</code>, <code>ata5702m322</code>, <code>at90pwm161</code>, <code>at90pwm216</code>, <code>at90pwm316</code>, <code>at90can32</code>, <code>at90can64</code>, <code>at90scr100</code>, <code>at90usb646</code>, <code>at90usb647</code>, <code>at94k</code>, <code>m3000</code>.

  128. </p>

  129. </dd>

  130. <dt><code>avr51</code></dt>

  131. <dd><p>&ldquo;Enhanced&rdquo; devices with 128&nbsp;KiB of program memory.

  132. <br><var>mcu</var>&nbsp;= <code>atmega128</code>, <code>atmega128a</code>, <code>atmega128rfa1</code>, <code>atmega128rfr2</code>, <code>atmega1280</code>, <code>atmega1281</code>, <code>atmega1284</code>, <code>atmega1284p</code>, <code>atmega1284rfr2</code>, <code>at90can128</code>, <code>at90usb1286</code>, <code>at90usb1287</code>.

  133. </p>

  134. </dd>

  135. <dt><code>avr6</code></dt>

  136. <dd><p>&ldquo;Enhanced&rdquo; devices with 3-byte PC, i.e. with more than 128&nbsp;KiB of program memory.

  137. <br><var>mcu</var>&nbsp;= <code>atmega256rfr2</code>, <code>atmega2560</code>, <code>atmega2561</code>, <code>atmega2564rfr2</code>.

  138. </p>

  139. </dd>

  140. <dt><code>avrxmega2</code></dt>

  141. <dd><p>&ldquo;XMEGA&rdquo; devices with more than 8&nbsp;KiB and up to 64&nbsp;KiB of program memory.

  142. <br><var>mcu</var>&nbsp;= <code>atxmega8e5</code>, <code>atxmega16a4</code>, <code>atxmega16a4u</code>, <code>atxmega16c4</code>, <code>atxmega16d4</code>, <code>atxmega16e5</code>, <code>atxmega32a4</code>, <code>atxmega32a4u</code>, <code>atxmega32c3</code>, <code>atxmega32c4</code>, <code>atxmega32d3</code>, <code>atxmega32d4</code>, <code>atxmega32e5</code>.

  143. </p>

  144. </dd>

  145. <dt><code>avrxmega3</code></dt>

  146. <dd><p>&ldquo;XMEGA&rdquo; devices with up to 64&nbsp;KiB of combined program memory and RAM, and with program memory visible in the RAM address space.

  147. <br><var>mcu</var>&nbsp;= <code>attiny202</code>, <code>attiny204</code>, <code>attiny212</code>, <code>attiny214</code>, <code>attiny402</code>, <code>attiny404</code>, <code>attiny406</code>, <code>attiny412</code>, <code>attiny414</code>, <code>attiny416</code>, <code>attiny417</code>, <code>attiny804</code>, <code>attiny806</code>, <code>attiny807</code>, <code>attiny814</code>, <code>attiny816</code>, <code>attiny817</code>, <code>attiny1604</code>, <code>attiny1606</code>, <code>attiny1607</code>, <code>attiny1614</code>, <code>attiny1616</code>, <code>attiny1617</code>, <code>attiny3214</code>, <code>attiny3216</code>, <code>attiny3217</code>, <code>atmega808</code>, <code>atmega809</code>, <code>atmega1608</code>, <code>atmega1609</code>, <code>atmega3208</code>, <code>atmega3209</code>, <code>atmega4808</code>, <code>atmega4809</code>.

  148. </p>

  149. </dd>

  150. <dt><code>avrxmega4</code></dt>

  151. <dd><p>&ldquo;XMEGA&rdquo; devices with more than 64&nbsp;KiB and up to 128&nbsp;KiB of program memory.

  152. <br><var>mcu</var>&nbsp;= <code>atxmega64a3</code>, <code>atxmega64a3u</code>, <code>atxmega64a4u</code>, <code>atxmega64b1</code>, <code>atxmega64b3</code>, <code>atxmega64c3</code>, <code>atxmega64d3</code>, <code>atxmega64d4</code>.

  153. </p>

  154. </dd>

  155. <dt><code>avrxmega5</code></dt>

  156. <dd><p>&ldquo;XMEGA&rdquo; devices with more than 64&nbsp;KiB and up to 128&nbsp;KiB of program memory and more than 64&nbsp;KiB of RAM.

  157. <br><var>mcu</var>&nbsp;= <code>atxmega64a1</code>, <code>atxmega64a1u</code>.

  158. </p>

  159. </dd>

  160. <dt><code>avrxmega6</code></dt>

  161. <dd><p>&ldquo;XMEGA&rdquo; devices with more than 128&nbsp;KiB of program memory.

  162. <br><var>mcu</var>&nbsp;= <code>atxmega128a3</code>, <code>atxmega128a3u</code>, <code>atxmega128b1</code>, <code>atxmega128b3</code>, <code>atxmega128c3</code>, <code>atxmega128d3</code>, <code>atxmega128d4</code>, <code>atxmega192a3</code>, <code>atxmega192a3u</code>, <code>atxmega192c3</code>, <code>atxmega192d3</code>, <code>atxmega256a3</code>, <code>atxmega256a3b</code>, <code>atxmega256a3bu</code>, <code>atxmega256a3u</code>, <code>atxmega256c3</code>, <code>atxmega256d3</code>, <code>atxmega384c3</code>, <code>atxmega384d3</code>.

  163. </p>

  164. </dd>

  165. <dt><code>avrxmega7</code></dt>

  166. <dd><p>&ldquo;XMEGA&rdquo; devices with more than 128&nbsp;KiB of program memory and more than 64&nbsp;KiB of RAM.

  167. <br><var>mcu</var>&nbsp;= <code>atxmega128a1</code>, <code>atxmega128a1u</code>, <code>atxmega128a4u</code>.

  168. </p>

  169. </dd>

  170. <dt><code>avrtiny</code></dt>

  171. <dd><p>&ldquo;TINY&rdquo; Tiny core devices with 512&nbsp;B up to 4&nbsp;KiB of program memory.

  172. <br><var>mcu</var>&nbsp;= <code>attiny4</code>, <code>attiny5</code>, <code>attiny9</code>, <code>attiny10</code>, <code>attiny20</code>, <code>attiny40</code>.

  173. </p>

  174. </dd>

  175. <dt><code>avr1</code></dt>

  176. <dd><p>This ISA is implemented by the minimal AVR core and supported for assembler only.

  177. <br><var>mcu</var>&nbsp;= <code>attiny11</code>, <code>attiny12</code>, <code>attiny15</code>, <code>attiny28</code>, <code>at90s1200</code>.

  178. </p>

  179. </dd>

  180. </dl>

  181. 

  182. </dd>

  183. <dt><code>-mabsdata</code></dt>

  184. <dd><a name="index-mabsdata"></a>

  185. 

  186. <p>Assume that all data in static storage can be accessed by LDS / STS

  187. instructions.  This option has only an effect on reduced Tiny devices like

  188. ATtiny40.  See also the <code>absdata</code>

  189. <a href="AVR-Variable-Attributes.html#AVR-Variable-Attributes">variable attribute</a>.

  190. </p>

  191. </dd>

  192. <dt><code>-maccumulate-args</code></dt>

  193. <dd><a name="index-maccumulate_002dargs"></a>

  194. <p>Accumulate outgoing function arguments and acquire/release the needed

  195. stack space for outgoing function arguments once in function

  196. prologue/epilogue.  Without this option, outgoing arguments are pushed

  197. before calling a function and popped afterwards.

  198. </p>

  199. <p>Popping the arguments after the function call can be expensive on

  200. AVR so that accumulating the stack space might lead to smaller

  201. executables because arguments need not be removed from the

  202. stack after such a function call.

  203. </p>

  204. <p>This option can lead to reduced code size for functions that perform

  205. several calls to functions that get their arguments on the stack like

  206. calls to printf-like functions.

  207. </p>

  208. </dd>

  209. <dt><code>-mbranch-cost=<var>cost</var></code></dt>

  210. <dd><a name="index-mbranch_002dcost-1"></a>

  211. <p>Set the branch costs for conditional branch instructions to

  212. <var>cost</var>.  Reasonable values for <var>cost</var> are small, non-negative

  213. integers. The default branch cost is 0.

  214. </p>

  215. </dd>

  216. <dt><code>-mcall-prologues</code></dt>

  217. <dd><a name="index-mcall_002dprologues"></a>

  218. <p>Functions prologues/epilogues are expanded as calls to appropriate

  219. subroutines.  Code size is smaller.

  220. </p>

  221. </dd>

  222. <dt><code>-mdouble=<var>bits</var></code></dt>

  223. <dt><code>-mlong-double=<var>bits</var></code></dt>

  224. <dd><a name="index-mdouble"></a>

  225. <a name="index-mlong_002ddouble"></a>

  226. <p>Set the size (in bits) of the <code>double</code> or <code>long double</code> type,

  227. respectively.  Possible values for <var>bits</var> are 32 and 64.

  228. Whether or not a specific value for <var>bits</var> is allowed depends on

  229. the <code>--with-double=</code> and <code>--with-long-double=</code>

  230. <a href="https://gcc.gnu.org/install/configure.html#avr">configure&nbsp;options</a><!-- /@w -->,

  231. and the same applies for the default values of the options.

  232. </p>

  233. </dd>

  234. <dt><code>-mgas-isr-prologues</code></dt>

  235. <dd><a name="index-mgas_002disr_002dprologues"></a>

  236. <p>Interrupt service routines (ISRs) may use the <code>__gcc_isr</code> pseudo

  237. instruction supported by GNU Binutils.

  238. If this option is on, the feature can still be disabled for individual

  239. ISRs by means of the <a href="AVR-Function-Attributes.html#AVR-Function-Attributes"><code>no_gccisr</code></a>

  240. function attribute.  This feature is activated per default

  241. if optimization is on (but not with <samp>-Og</samp>, see <a href="Optimize-Options.html#Optimize-Options">Optimize Options</a>),

  242. and if GNU Binutils support <a href="https://sourceware.org/PR21683">PR21683</a><!-- /@w -->.

  243. </p>

  244. </dd>

  245. <dt><code>-mint8</code></dt>

  246. <dd><a name="index-mint8"></a>

  247. <p>Assume <code>int</code> to be 8-bit integer.  This affects the sizes of all types: a

  248. <code>char</code> is 1 byte, an <code>int</code> is 1 byte, a <code>long</code> is 2 bytes,

  249. and <code>long long</code> is 4 bytes.  Please note that this option does not

  250. conform to the C standards, but it results in smaller code

  251. size.

  252. </p>

  253. </dd>

  254. <dt><code>-mmain-is-OS_task</code></dt>

  255. <dd><a name="index-mmain_002dis_002dOS_005ftask"></a>

  256. <p>Do not save registers in <code>main</code>.  The effect is the same like

  257. attaching attribute <a href="AVR-Function-Attributes.html#AVR-Function-Attributes"><code>OS_task</code></a>

  258. to <code>main</code>. It is activated per default if optimization is on.

  259. </p>

  260. </dd>

  261. <dt><code>-mn-flash=<var>num</var></code></dt>

  262. <dd><a name="index-mn_002dflash"></a>

  263. <p>Assume that the flash memory has a size of 

  264. <var>num</var> times 64&nbsp;KiB.

  265. </p>

  266. </dd>

  267. <dt><code>-mno-interrupts</code></dt>

  268. <dd><a name="index-mno_002dinterrupts"></a>

  269. <p>Generated code is not compatible with hardware interrupts.

  270. Code size is smaller.

  271. </p>

  272. </dd>

  273. <dt><code>-mrelax</code></dt>

  274. <dd><a name="index-mrelax"></a>

  275. <p>Try to replace <code>CALL</code> resp. <code>JMP</code> instruction by the shorter

  276. <code>RCALL</code> resp. <code>RJMP</code> instruction if applicable.

  277. Setting <samp>-mrelax</samp> just adds the <samp>--mlink-relax</samp> option to

  278. the assembler&rsquo;s command line and the <samp>--relax</samp> option to the

  279. linker&rsquo;s command line.

  280. </p>

  281. <p>Jump relaxing is performed by the linker because jump offsets are not

  282. known before code is located. Therefore, the assembler code generated by the

  283. compiler is the same, but the instructions in the executable may

  284. differ from instructions in the assembler code.

  285. </p>

  286. <p>Relaxing must be turned on if linker stubs are needed, see the

  287. section on <code>EIND</code> and linker stubs below.

  288. </p>

  289. </dd>

  290. <dt><code>-mrmw</code></dt>

  291. <dd><a name="index-mrmw"></a>

  292. <p>Assume that the device supports the Read-Modify-Write

  293. instructions <code>XCH</code>, <code>LAC</code>, <code>LAS</code> and <code>LAT</code>.

  294. </p>

  295. </dd>

  296. <dt><code>-mshort-calls</code></dt>

  297. <dd><a name="index-mshort_002dcalls"></a>

  298. 

  299. <p>Assume that <code>RJMP</code> and <code>RCALL</code> can target the whole

  300. program memory.

  301. </p>

  302. <p>This option is used internally for multilib selection.  It is

  303. not an optimization option, and you don&rsquo;t need to set it by hand.

  304. </p>

  305. </dd>

  306. <dt><code>-msp8</code></dt>

  307. <dd><a name="index-msp8"></a>

  308. <p>Treat the stack pointer register as an 8-bit register,

  309. i.e. assume the high byte of the stack pointer is zero.

  310. In general, you don&rsquo;t need to set this option by hand.

  311. </p>

  312. <p>This option is used internally by the compiler to select and

  313. build multilibs for architectures <code>avr2</code> and <code>avr25</code>.

  314. These architectures mix devices with and without <code>SPH</code>.

  315. For any setting other than <samp>-mmcu=avr2</samp> or <samp>-mmcu=avr25</samp>

  316. the compiler driver adds or removes this option from the compiler

  317. proper&rsquo;s command line, because the compiler then knows if the device

  318. or architecture has an 8-bit stack pointer and thus no <code>SPH</code>

  319. register or not.

  320. </p>

  321. </dd>

  322. <dt><code>-mstrict-X</code></dt>

  323. <dd><a name="index-mstrict_002dX"></a>

  324. <p>Use address register <code>X</code> in a way proposed by the hardware.  This means

  325. that <code>X</code> is only used in indirect, post-increment or

  326. pre-decrement addressing.

  327. </p>

  328. <p>Without this option, the <code>X</code> register may be used in the same way

  329. as <code>Y</code> or <code>Z</code> which then is emulated by additional

  330. instructions.  

  331. For example, loading a value with <code>X+const</code> addressing with a

  332. small non-negative <code>const &lt; 64</code> to a register <var>Rn</var> is

  333. performed as

  334. </p>

  335. <div class="example">

  336. <pre class="example">adiw r26, const   ; X += const

  337. ld   <var>Rn</var>, X        ; <var>Rn</var> = *X

  338. sbiw r26, const   ; X -= const

  339. </pre></div>

  340. 

  341. </dd>

  342. <dt><code>-mtiny-stack</code></dt>

  343. <dd><a name="index-mtiny_002dstack"></a>

  344. <p>Only change the lower 8&nbsp;bits of the stack pointer.

  345. </p>

  346. </dd>

  347. <dt><code>-mfract-convert-truncate</code></dt>

  348. <dd><a name="index-mfract_002dconvert_002dtruncate"></a>

  349. <p>Allow to use truncation instead of rounding towards zero for fractional fixed-point types.

  350. </p>

  351. </dd>

  352. <dt><code>-nodevicelib</code></dt>

  353. <dd><a name="index-nodevicelib"></a>

  354. <p>Don&rsquo;t link against AVR-LibC&rsquo;s device specific library <code>lib&lt;mcu&gt;.a</code>.

  355. </p>

  356. </dd>

  357. <dt><code>-nodevicespecs</code></dt>

  358. <dd><a name="index-nodevicespecs"></a>

  359. <p>Don&rsquo;t add <samp>-specs=device-specs/specs-<var>mcu</var></samp> to the compiler driver&rsquo;s

  360. command line.  The user takes responsibility for supplying the sub-processes

  361. like compiler proper, assembler and linker with appropriate command line

  362. options.  This means that the user has to supply her private device specs

  363. file by means of <samp>-specs=<var>path-to-specs-file</var></samp>.  There is no

  364. more need for option <samp>-mmcu=<var>mcu</var></samp>.

  365. </p>

  366. <p>This option can also serve as a replacement for the older way of

  367. specifying custom device-specs files that needed <samp>-B <var>some-path</var></samp> to point to a directory

  368. which contains a folder named <code>device-specs</code> which contains a specs file named

  369. <code>specs-<var>mcu</var></code>, where <var>mcu</var> was specified by <samp>-mmcu=<var>mcu</var></samp>.

  370. </p>

  371. </dd>

  372. <dt><code>-Waddr-space-convert</code></dt>

  373. <dd><a name="index-Waddr_002dspace_002dconvert"></a>

  374. <a name="index-Wno_002daddr_002dspace_002dconvert"></a>

  375. <p>Warn about conversions between address spaces in the case where the

  376. resulting address space is not contained in the incoming address space.

  377. </p>

  378. </dd>

  379. <dt><code>-Wmisspelled-isr</code></dt>

  380. <dd><a name="index-Wmisspelled_002disr"></a>

  381. <a name="index-Wno_002dmisspelled_002disr"></a>

  382. <p>Warn if the ISR is misspelled, i.e. without __vector prefix.

  383. Enabled by default.

  384. </p></dd>

  385. </dl>

  386. 

  387. <a name="EIND-and-Devices-with-More-Than-128-Ki-Bytes-of-Flash"></a>

  388. <h4 class="subsubsection">3.19.6.1 <code>EIND</code> and Devices with More Than 128 Ki Bytes of Flash</h4>

  389. <a name="index-EIND"></a>

  390. <p>Pointers in the implementation are 16&nbsp;bits wide.

  391. The address of a function or label is represented as word address so

  392. that indirect jumps and calls can target any code address in the

  393. range of 64&nbsp;Ki words.

  394. </p>

  395. <p>In order to facilitate indirect jump on devices with more than 128&nbsp;Ki

  396. bytes of program memory space, there is a special function register called

  397. <code>EIND</code> that serves as most significant part of the target address

  398. when <code>EICALL</code> or <code>EIJMP</code> instructions are used.

  399. </p>

  400. <p>Indirect jumps and calls on these devices are handled as follows by

  401. the compiler and are subject to some limitations:

  402. </p>

  403. <ul>

  404. <li> The compiler never sets <code>EIND</code>.

  405. 

  406. </li><li> The compiler uses <code>EIND</code> implicitly in <code>EICALL</code>/<code>EIJMP</code>

  407. instructions or might read <code>EIND</code> directly in order to emulate an

  408. indirect call/jump by means of a <code>RET</code> instruction.

  409. 

  410. </li><li> The compiler assumes that <code>EIND</code> never changes during the startup

  411. code or during the application. In particular, <code>EIND</code> is not

  412. saved/restored in function or interrupt service routine

  413. prologue/epilogue.

  414. 

  415. </li><li> For indirect calls to functions and computed goto, the linker

  416. generates <em>stubs</em>. Stubs are jump pads sometimes also called

  417. <em>trampolines</em>. Thus, the indirect call/jump jumps to such a stub.

  418. The stub contains a direct jump to the desired address.

  419. 

  420. </li><li> Linker relaxation must be turned on so that the linker generates

  421. the stubs correctly in all situations. See the compiler option

  422. <samp>-mrelax</samp> and the linker option <samp>--relax</samp>.

  423. There are corner cases where the linker is supposed to generate stubs

  424. but aborts without relaxation and without a helpful error message.

  425. 

  426. </li><li> The default linker script is arranged for code with <code>EIND = 0</code>.

  427. If code is supposed to work for a setup with <code>EIND != 0</code>, a custom

  428. linker script has to be used in order to place the sections whose

  429. name start with <code>.trampolines</code> into the segment where <code>EIND</code>

  430. points to.

  431. 

  432. </li><li> The startup code from libgcc never sets <code>EIND</code>.

  433. Notice that startup code is a blend of code from libgcc and AVR-LibC.

  434. For the impact of AVR-LibC on <code>EIND</code>, see the

  435. <a href="http://nongnu.org/avr-libc/user-manual/"><span class="nolinebreak">AVR-LibC</span>&nbsp;user&nbsp;manual</a><!-- /@w -->.

  436. 

  437. </li><li> It is legitimate for user-specific startup code to set up <code>EIND</code>

  438. early, for example by means of initialization code located in

  439. section <code>.init3</code>. Such code runs prior to general startup code

  440. that initializes RAM and calls constructors, but after the bit

  441. of startup code from AVR-LibC that sets <code>EIND</code> to the segment

  442. where the vector table is located.

  443. <div class="example">

  444. <pre class="example">#include &lt;avr/io.h&gt;

  445. 

  446. static void

  447. __attribute__((section(&quot;.init3&quot;),naked,used,no_instrument_function))

  448. init3_set_eind (void)

  449. {

  450.   __asm volatile (&quot;ldi r24,pm_hh8(__trampolines_start)\n\t&quot;

  451.                   &quot;out %i0,r24&quot; :: &quot;n&quot; (&amp;EIND) : &quot;r24&quot;,&quot;memory&quot;);

  452. }

  453. </pre></div>

  454. 

  455. <p>The <code>__trampolines_start</code> symbol is defined in the linker script.

  456. </p>

  457. </li><li> Stubs are generated automatically by the linker if

  458. the following two conditions are met:

  459. <ul class="no-bullet">

  460. <li>- The address of a label is taken by means of the <code>gs</code> modifier

  461. (short for <em>generate stubs</em>) like so:

  462. <div class="example">

  463. <pre class="example">LDI r24, lo8(gs(<var>func</var>))

  464. LDI r25, hi8(gs(<var>func</var>))

  465. </pre></div>

  466. </li><li>- The final location of that label is in a code segment

  467. <em>outside</em> the segment where the stubs are located.

  468. </li></ul>

  469. 

  470. </li><li> The compiler emits such <code>gs</code> modifiers for code labels in the

  471. following situations:

  472. <ul class="no-bullet">

  473. <li>- Taking address of a function or code label.

  474. </li><li>- Computed goto.

  475. </li><li>- If prologue-save function is used, see <samp>-mcall-prologues</samp>

  476. command-line option.

  477. </li><li>- Switch/case dispatch tables. If you do not want such dispatch

  478. tables you can specify the <samp>-fno-jump-tables</samp> command-line option.

  479. </li><li>- C and C++ constructors/destructors called during startup/shutdown.

  480. </li><li>- If the tools hit a <code>gs()</code> modifier explained above.

  481. </li></ul>

  482. 

  483. </li><li> Jumping to non-symbolic addresses like so is <em>not</em> supported:

  484. 

  485. <div class="example">

  486. <pre class="example">int main (void)

  487. {

  488.     /* Call function at word address 0x2 */

  489.     return ((int(*)(void)) 0x2)();

  490. }

  491. </pre></div>

  492. 

  493. <p>Instead, a stub has to be set up, i.e. the function has to be called

  494. through a symbol (<code>func_4</code> in the example):

  495. </p>

  496. <div class="example">

  497. <pre class="example">int main (void)

  498. {

  499.     extern int func_4 (void);

  500. 

  501.     /* Call function at byte address 0x4 */

  502.     return func_4();

  503. }

  504. </pre></div>

  505. 

  506. <p>and the application be linked with <samp>-Wl,--defsym,func_4=0x4</samp>.

  507. Alternatively, <code>func_4</code> can be defined in the linker script.

  508. </p></li></ul>

  509. 

  510. <a name="Handling-of-the-RAMPD_002c-RAMPX_002c-RAMPY-and-RAMPZ-Special-Function-Registers"></a>

  511. <h4 class="subsubsection">3.19.6.2 Handling of the <code>RAMPD</code>, <code>RAMPX</code>, <code>RAMPY</code> and <code>RAMPZ</code> Special Function Registers</h4>

  512. <a name="index-RAMPD"></a>

  513. <a name="index-RAMPX"></a>

  514. <a name="index-RAMPY"></a>

  515. <a name="index-RAMPZ"></a>

  516. <p>Some AVR devices support memories larger than the 64&nbsp;KiB range

  517. that can be accessed with 16-bit pointers.  To access memory locations

  518. outside this 64&nbsp;KiB range, the content of a <code>RAMP</code>

  519. register is used as high part of the address:

  520. The <code>X</code>, <code>Y</code>, <code>Z</code> address register is concatenated

  521. with the <code>RAMPX</code>, <code>RAMPY</code>, <code>RAMPZ</code> special function

  522. register, respectively, to get a wide address. Similarly,

  523. <code>RAMPD</code> is used together with direct addressing.

  524. </p>

  525. <ul>

  526. <li> The startup code initializes the <code>RAMP</code> special function

  527. registers with zero.

  528. 

  529. </li><li> If a <a href="Named-Address-Spaces.html#AVR-Named-Address-Spaces">named address space</a> other than

  530. generic or <code>__flash</code> is used, then <code>RAMPZ</code> is set

  531. as needed before the operation.

  532. 

  533. </li><li> If the device supports RAM larger than 64&nbsp;KiB and the compiler

  534. needs to change <code>RAMPZ</code> to accomplish an operation, <code>RAMPZ</code>

  535. is reset to zero after the operation.

  536. 

  537. </li><li> If the device comes with a specific <code>RAMP</code> register, the ISR

  538. prologue/epilogue saves/restores that SFR and initializes it with

  539. zero in case the ISR code might (implicitly) use it.

  540. 

  541. </li><li> RAM larger than 64&nbsp;KiB is not supported by GCC for AVR targets.

  542. If you use inline assembler to read from locations outside the

  543. 16-bit address range and change one of the <code>RAMP</code> registers,

  544. you must reset it to zero after the access.

  545. 

  546. </li></ul>

  547. 

  548. <a name="AVR-Built_002din-Macros"></a>

  549. <h4 class="subsubsection">3.19.6.3 AVR Built-in Macros</h4>

  550. 

  551. <p>GCC defines several built-in macros so that the user code can test

  552. for the presence or absence of features.  Almost any of the following

  553. built-in macros are deduced from device capabilities and thus

  554. triggered by the <samp>-mmcu=</samp> command-line option.

  555. </p>

  556. <p>For even more AVR-specific built-in macros see

  557. <a href="Named-Address-Spaces.html#AVR-Named-Address-Spaces">AVR Named Address Spaces</a> and <a href="AVR-Built_002din-Functions.html#AVR-Built_002din-Functions">AVR Built-in Functions</a>.

  558. </p>

  559. <dl compact="compact">

  560. <dt><code>__AVR_ARCH__</code></dt>

  561. <dd><p>Build-in macro that resolves to a decimal number that identifies the

  562. architecture and depends on the <samp>-mmcu=<var>mcu</var></samp> option.

  563. Possible values are:

  564. </p>

  565. <p><code>2</code>, <code>25</code>, <code>3</code>, <code>31</code>, <code>35</code>,

  566. <code>4</code>, <code>5</code>, <code>51</code>, <code>6</code>

  567. </p>

  568. <p>for <var>mcu</var>=<code>avr2</code>, <code>avr25</code>, <code>avr3</code>, <code>avr31</code>,

  569. <code>avr35</code>, <code>avr4</code>, <code>avr5</code>, <code>avr51</code>, <code>avr6</code>,

  570. </p>

  571. <p>respectively and

  572. </p>

  573. <p><code>100</code>,

  574. <code>102</code>, <code>103</code>, <code>104</code>,

  575. <code>105</code>, <code>106</code>, <code>107</code>

  576. </p>

  577. <p>for <var>mcu</var>=<code>avrtiny</code>,

  578. <code>avrxmega2</code>, <code>avrxmega3</code>, <code>avrxmega4</code>,

  579. <code>avrxmega5</code>, <code>avrxmega6</code>, <code>avrxmega7</code>, respectively.

  580. If <var>mcu</var> specifies a device, this built-in macro is set

  581. accordingly. For example, with <samp>-mmcu=atmega8</samp> the macro is

  582. defined to <code>4</code>.

  583. </p>

  584. </dd>

  585. <dt><code>__AVR_<var>Device</var>__</code></dt>

  586. <dd><p>Setting <samp>-mmcu=<var>device</var></samp> defines this built-in macro which reflects

  587. the device&rsquo;s name. For example, <samp>-mmcu=atmega8</samp> defines the

  588. built-in macro <code>__AVR_ATmega8__</code>, <samp>-mmcu=attiny261a</samp> defines

  589. <code>__AVR_ATtiny261A__</code>, etc.

  590. </p>

  591. <p>The built-in macros&rsquo; names follow

  592. the scheme <code>__AVR_<var>Device</var>__</code> where <var>Device</var> is

  593. the device name as from the AVR user manual. The difference between

  594. <var>Device</var> in the built-in macro and <var>device</var> in

  595. <samp>-mmcu=<var>device</var></samp> is that the latter is always lowercase.

  596. </p>

  597. <p>If <var>device</var> is not a device but only a core architecture like

  598. &lsquo;<samp>avr51</samp>&rsquo;, this macro is not defined.

  599. </p>

  600. </dd>

  601. <dt><code>__AVR_DEVICE_NAME__</code></dt>

  602. <dd><p>Setting <samp>-mmcu=<var>device</var></samp> defines this built-in macro to

  603. the device&rsquo;s name. For example, with <samp>-mmcu=atmega8</samp> the macro

  604. is defined to <code>atmega8</code>.

  605. </p>

  606. <p>If <var>device</var> is not a device but only a core architecture like

  607. &lsquo;<samp>avr51</samp>&rsquo;, this macro is not defined.

  608. </p>

  609. </dd>

  610. <dt><code>__AVR_XMEGA__</code></dt>

  611. <dd><p>The device / architecture belongs to the XMEGA family of devices.

  612. </p>

  613. </dd>

  614. <dt><code>__AVR_HAVE_ELPM__</code></dt>

  615. <dd><p>The device has the <code>ELPM</code> instruction.

  616. </p>

  617. </dd>

  618. <dt><code>__AVR_HAVE_ELPMX__</code></dt>

  619. <dd><p>The device has the <code>ELPM R<var>n</var>,Z</code> and <code>ELPM

  620. R<var>n</var>,Z+</code> instructions.

  621. </p>

  622. </dd>

  623. <dt><code>__AVR_HAVE_MOVW__</code></dt>

  624. <dd><p>The device has the <code>MOVW</code> instruction to perform 16-bit

  625. register-register moves.

  626. </p>

  627. </dd>

  628. <dt><code>__AVR_HAVE_LPMX__</code></dt>

  629. <dd><p>The device has the <code>LPM R<var>n</var>,Z</code> and

  630. <code>LPM R<var>n</var>,Z+</code> instructions.

  631. </p>

  632. </dd>

  633. <dt><code>__AVR_HAVE_MUL__</code></dt>

  634. <dd><p>The device has a hardware multiplier. 

  635. </p>

  636. </dd>

  637. <dt><code>__AVR_HAVE_JMP_CALL__</code></dt>

  638. <dd><p>The device has the <code>JMP</code> and <code>CALL</code> instructions.

  639. This is the case for devices with more than 8&nbsp;KiB of program

  640. memory.

  641. </p>

  642. </dd>

  643. <dt><code>__AVR_HAVE_EIJMP_EICALL__</code></dt>

  644. <dt><code>__AVR_3_BYTE_PC__</code></dt>

  645. <dd><p>The device has the <code>EIJMP</code> and <code>EICALL</code> instructions.

  646. This is the case for devices with more than 128&nbsp;KiB of program memory.

  647. This also means that the program counter

  648. (PC) is 3&nbsp;bytes wide.

  649. </p>

  650. </dd>

  651. <dt><code>__AVR_2_BYTE_PC__</code></dt>

  652. <dd><p>The program counter (PC) is 2&nbsp;bytes wide. This is the case for devices

  653. with up to 128&nbsp;KiB of program memory.

  654. </p>

  655. </dd>

  656. <dt><code>__AVR_HAVE_8BIT_SP__</code></dt>

  657. <dt><code>__AVR_HAVE_16BIT_SP__</code></dt>

  658. <dd><p>The stack pointer (SP) register is treated as 8-bit respectively

  659. 16-bit register by the compiler.

  660. The definition of these macros is affected by <samp>-mtiny-stack</samp>.

  661. </p>

  662. </dd>

  663. <dt><code>__AVR_HAVE_SPH__</code></dt>

  664. <dt><code>__AVR_SP8__</code></dt>

  665. <dd><p>The device has the SPH (high part of stack pointer) special function

  666. register or has an 8-bit stack pointer, respectively.

  667. The definition of these macros is affected by <samp>-mmcu=</samp> and

  668. in the cases of <samp>-mmcu=avr2</samp> and <samp>-mmcu=avr25</samp> also

  669. by <samp>-msp8</samp>.

  670. </p>

  671. </dd>

  672. <dt><code>__AVR_HAVE_RAMPD__</code></dt>

  673. <dt><code>__AVR_HAVE_RAMPX__</code></dt>

  674. <dt><code>__AVR_HAVE_RAMPY__</code></dt>

  675. <dt><code>__AVR_HAVE_RAMPZ__</code></dt>

  676. <dd><p>The device has the <code>RAMPD</code>, <code>RAMPX</code>, <code>RAMPY</code>,

  677. <code>RAMPZ</code> special function register, respectively.

  678. </p>

  679. </dd>

  680. <dt><code>__NO_INTERRUPTS__</code></dt>

  681. <dd><p>This macro reflects the <samp>-mno-interrupts</samp> command-line option.

  682. </p>

  683. </dd>

  684. <dt><code>__AVR_ERRATA_SKIP__</code></dt>

  685. <dt><code>__AVR_ERRATA_SKIP_JMP_CALL__</code></dt>

  686. <dd><p>Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit

  687. instructions because of a hardware erratum.  Skip instructions are

  688. <code>SBRS</code>, <code>SBRC</code>, <code>SBIS</code>, <code>SBIC</code> and <code>CPSE</code>.

  689. The second macro is only defined if <code>__AVR_HAVE_JMP_CALL__</code> is also

  690. set.

  691. </p>

  692. </dd>

  693. <dt><code>__AVR_ISA_RMW__</code></dt>

  694. <dd><p>The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT).

  695. </p>

  696. </dd>

  697. <dt><code>__AVR_SFR_OFFSET__=<var>offset</var></code></dt>

  698. <dd><p>Instructions that can address I/O special function registers directly

  699. like <code>IN</code>, <code>OUT</code>, <code>SBI</code>, etc. may use a different

  700. address as if addressed by an instruction to access RAM like <code>LD</code>

  701. or <code>STS</code>. This offset depends on the device architecture and has

  702. to be subtracted from the RAM address in order to get the

  703. respective I/O&nbsp;address.

  704. </p>

  705. </dd>

  706. <dt><code>__AVR_SHORT_CALLS__</code></dt>

  707. <dd><p>The <samp>-mshort-calls</samp> command line option is set.

  708. </p>

  709. </dd>

  710. <dt><code>__AVR_PM_BASE_ADDRESS__=<var>addr</var></code></dt>

  711. <dd><p>Some devices support reading from flash memory by means of <code>LD*</code>

  712. instructions.  The flash memory is seen in the data address space

  713. at an offset of <code>__AVR_PM_BASE_ADDRESS__</code>.  If this macro

  714. is not defined, this feature is not available.  If defined,

  715. the address space is linear and there is no need to put

  716. <code>.rodata</code> into RAM.  This is handled by the default linker

  717. description file, and is currently available for

  718. <code>avrtiny</code> and <code>avrxmega3</code>.  Even more convenient,

  719. there is no need to use address spaces like <code>__flash</code> or

  720. features like attribute <code>progmem</code> and <code>pgm_read_*</code>.

  721. </p>

  722. </dd>

  723. <dt><code>__WITH_AVRLIBC__</code></dt>

  724. <dd><p>The compiler is configured to be used together with AVR-Libc.

  725. See the <samp>--with-avrlibc</samp> configure option.

  726. </p>

  727. </dd>

  728. <dt><code>__HAVE_DOUBLE_MULTILIB__</code></dt>

  729. <dd><p>Defined if <samp>-mdouble=</samp> acts as a multilib option.

  730. </p>

  731. </dd>

  732. <dt><code>__HAVE_DOUBLE32__</code></dt>

  733. <dt><code>__HAVE_DOUBLE64__</code></dt>

  734. <dd><p>Defined if the compiler supports 32-bit double resp. 64-bit double.

  735. The actual layout is specified by option <samp>-mdouble=</samp>.

  736. </p>

  737. </dd>

  738. <dt><code>__DEFAULT_DOUBLE__</code></dt>

  739. <dd><p>The size in bits of <code>double</code> if <samp>-mdouble=</samp> is not set.

  740. To test the layout of <code>double</code> in a program, use the built-in

  741. macro <code>__SIZEOF_DOUBLE__</code>.

  742. </p>

  743. </dd>

  744. <dt><code>__HAVE_LONG_DOUBLE32__</code></dt>

  745. <dt><code>__HAVE_LONG_DOUBLE64__</code></dt>

  746. <dt><code>__HAVE_LONG_DOUBLE_MULTILIB__</code></dt>

  747. <dt><code>__DEFAULT_LONG_DOUBLE__</code></dt>

  748. <dd><p>Same as above, but for <code>long double</code> instead of <code>double</code>.

  749. </p>

  750. </dd>

  751. <dt><code>__WITH_DOUBLE_COMPARISON__</code></dt>

  752. <dd><p>Reflects the <code>--with-double-comparison={tristate|bool|libf7}</code>

  753. <a href="https://gcc.gnu.org/install/configure.html#avr">configure&nbsp;option</a><!-- /@w -->

  754. and is defined to <code>2</code> or <code>3</code>.

  755. </p>

  756. </dd>

  757. <dt><code>__WITH_LIBF7_LIBGCC__</code></dt>

  758. <dt><code>__WITH_LIBF7_MATH__</code></dt>

  759. <dt><code>__WITH_LIBF7_MATH_SYMBOLS__</code></dt>

  760. <dd><p>Reflects the <code>--with-libf7={libgcc|math|math-symbols}</code>

  761. <a href="https://gcc.gnu.org/install/configure.html#avr">configure&nbsp;option</a><!-- /@w -->.

  762. </p>

  763. </dd>

  764. </dl>

  765. 

  766. <hr>

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  768. <p>

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