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  61. <a name="AVR-Options"></a>
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  66. <hr>
  67. <a name="AVR-Options-1"></a>
  68. <h4 class="subsection">3.19.6 AVR Options</h4>
  69. <a name="index-AVR-Options"></a>
  70. <p>These options are defined for AVR implementations:
  71. </p>
  72. <dl compact="compact">
  73. <dt><code>-mmcu=<var>mcu</var></code></dt>
  74. <dd><a name="index-mmcu"></a>
  75. <p>Specify Atmel AVR instruction set architectures (ISA) or MCU type.
  76. </p>
  77. <p>The default for this option is&nbsp;&lsquo;<samp>avr2</samp>&rsquo;.
  78. </p>
  79. <p>GCC supports the following AVR devices and ISAs:
  80. </p>
  81. <dl compact="compact">
  82. <dt><code>avr2</code></dt>
  83. <dd><p>&ldquo;Classic&rdquo; devices with up to 8&nbsp;KiB of program memory.
  84. <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>.
  85. </p>
  86. </dd>
  87. <dt><code>avr25</code></dt>
  88. <dd><p>&ldquo;Classic&rdquo; devices with up to 8&nbsp;KiB of program memory and with the <code>MOVW</code> instruction.
  89. <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>.
  90. </p>
  91. </dd>
  92. <dt><code>avr3</code></dt>
  93. <dd><p>&ldquo;Classic&rdquo; devices with 16&nbsp;KiB up to 64&nbsp;KiB of program memory.
  94. <br><var>mcu</var>&nbsp;= <code>at76c711</code>, <code>at43usb355</code>.
  95. </p>
  96. </dd>
  97. <dt><code>avr31</code></dt>
  98. <dd><p>&ldquo;Classic&rdquo; devices with 128&nbsp;KiB of program memory.
  99. <br><var>mcu</var>&nbsp;= <code>atmega103</code>, <code>at43usb320</code>.
  100. </p>
  101. </dd>
  102. <dt><code>avr35</code></dt>
  103. <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.
  104. <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>.
  105. </p>
  106. </dd>
  107. <dt><code>avr4</code></dt>
  108. <dd><p>&ldquo;Enhanced&rdquo; devices with up to 8&nbsp;KiB of program memory.
  109. <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>.
  110. </p>
  111. </dd>
  112. <dt><code>avr5</code></dt>
  113. <dd><p>&ldquo;Enhanced&rdquo; devices with 16&nbsp;KiB up to 64&nbsp;KiB of program memory.
  114. <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>.
  115. </p>
  116. </dd>
  117. <dt><code>avr51</code></dt>
  118. <dd><p>&ldquo;Enhanced&rdquo; devices with 128&nbsp;KiB of program memory.
  119. <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>.
  120. </p>
  121. </dd>
  122. <dt><code>avr6</code></dt>
  123. <dd><p>&ldquo;Enhanced&rdquo; devices with 3-byte PC, i.e. with more than 128&nbsp;KiB of program memory.
  124. <br><var>mcu</var>&nbsp;= <code>atmega256rfr2</code>, <code>atmega2560</code>, <code>atmega2561</code>, <code>atmega2564rfr2</code>.
  125. </p>
  126. </dd>
  127. <dt><code>avrxmega2</code></dt>
  128. <dd><p>&ldquo;XMEGA&rdquo; devices with more than 8&nbsp;KiB and up to 64&nbsp;KiB of program memory.
  129. <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>.
  130. </p>
  131. </dd>
  132. <dt><code>avrxmega3</code></dt>
  133. <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.
  134. <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>.
  135. </p>
  136. </dd>
  137. <dt><code>avrxmega4</code></dt>
  138. <dd><p>&ldquo;XMEGA&rdquo; devices with more than 64&nbsp;KiB and up to 128&nbsp;KiB of program memory.
  139. <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>.
  140. </p>
  141. </dd>
  142. <dt><code>avrxmega5</code></dt>
  143. <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.
  144. <br><var>mcu</var>&nbsp;= <code>atxmega64a1</code>, <code>atxmega64a1u</code>.
  145. </p>
  146. </dd>
  147. <dt><code>avrxmega6</code></dt>
  148. <dd><p>&ldquo;XMEGA&rdquo; devices with more than 128&nbsp;KiB of program memory.
  149. <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>.
  150. </p>
  151. </dd>
  152. <dt><code>avrxmega7</code></dt>
  153. <dd><p>&ldquo;XMEGA&rdquo; devices with more than 128&nbsp;KiB of program memory and more than 64&nbsp;KiB of RAM.
  154. <br><var>mcu</var>&nbsp;= <code>atxmega128a1</code>, <code>atxmega128a1u</code>, <code>atxmega128a4u</code>.
  155. </p>
  156. </dd>
  157. <dt><code>avrtiny</code></dt>
  158. <dd><p>&ldquo;TINY&rdquo; Tiny core devices with 512&nbsp;B up to 4&nbsp;KiB of program memory.
  159. <br><var>mcu</var>&nbsp;= <code>attiny4</code>, <code>attiny5</code>, <code>attiny9</code>, <code>attiny10</code>, <code>attiny20</code>, <code>attiny40</code>.
  160. </p>
  161. </dd>
  162. <dt><code>avr1</code></dt>
  163. <dd><p>This ISA is implemented by the minimal AVR core and supported for assembler only.
  164. <br><var>mcu</var>&nbsp;= <code>attiny11</code>, <code>attiny12</code>, <code>attiny15</code>, <code>attiny28</code>, <code>at90s1200</code>.
  165. </p>
  166. </dd>
  167. </dl>
  168. </dd>
  169. <dt><code>-mabsdata</code></dt>
  170. <dd><a name="index-mabsdata"></a>
  171. <p>Assume that all data in static storage can be accessed by LDS / STS
  172. instructions. This option has only an effect on reduced Tiny devices like
  173. ATtiny40. See also the <code>absdata</code>
  174. <a href="AVR-Variable-Attributes.html#AVR-Variable-Attributes">variable attribute</a>.
  175. </p>
  176. </dd>
  177. <dt><code>-maccumulate-args</code></dt>
  178. <dd><a name="index-maccumulate_002dargs"></a>
  179. <p>Accumulate outgoing function arguments and acquire/release the needed
  180. stack space for outgoing function arguments once in function
  181. prologue/epilogue. Without this option, outgoing arguments are pushed
  182. before calling a function and popped afterwards.
  183. </p>
  184. <p>Popping the arguments after the function call can be expensive on
  185. AVR so that accumulating the stack space might lead to smaller
  186. executables because arguments need not be removed from the
  187. stack after such a function call.
  188. </p>
  189. <p>This option can lead to reduced code size for functions that perform
  190. several calls to functions that get their arguments on the stack like
  191. calls to printf-like functions.
  192. </p>
  193. </dd>
  194. <dt><code>-mbranch-cost=<var>cost</var></code></dt>
  195. <dd><a name="index-mbranch_002dcost-1"></a>
  196. <p>Set the branch costs for conditional branch instructions to
  197. <var>cost</var>. Reasonable values for <var>cost</var> are small, non-negative
  198. integers. The default branch cost is 0.
  199. </p>
  200. </dd>
  201. <dt><code>-mcall-prologues</code></dt>
  202. <dd><a name="index-mcall_002dprologues"></a>
  203. <p>Functions prologues/epilogues are expanded as calls to appropriate
  204. subroutines. Code size is smaller.
  205. </p>
  206. </dd>
  207. <dt><code>-mdouble=<var>bits</var></code></dt>
  208. <dt><code>-mlong-double=<var>bits</var></code></dt>
  209. <dd><a name="index-mdouble"></a>
  210. <a name="index-mlong_002ddouble"></a>
  211. <p>Set the size (in bits) of the <code>double</code> or <code>long double</code> type,
  212. respectively. Possible values for <var>bits</var> are 32 and 64.
  213. Whether or not a specific value for <var>bits</var> is allowed depends on
  214. the <code>--with-double=</code> and <code>--with-long-double=</code>
  215. <a href="https://gcc.gnu.org/install/configure.html#avr">configure&nbsp;options</a><!-- /@w -->,
  216. and the same applies for the default values of the options.
  217. </p>
  218. </dd>
  219. <dt><code>-mgas-isr-prologues</code></dt>
  220. <dd><a name="index-mgas_002disr_002dprologues"></a>
  221. <p>Interrupt service routines (ISRs) may use the <code>__gcc_isr</code> pseudo
  222. instruction supported by GNU Binutils.
  223. If this option is on, the feature can still be disabled for individual
  224. ISRs by means of the <a href="AVR-Function-Attributes.html#AVR-Function-Attributes"><code>no_gccisr</code></a>
  225. function attribute. This feature is activated per default
  226. if optimization is on (but not with <samp>-Og</samp>, see <a href="Optimize-Options.html#Optimize-Options">Optimize Options</a>),
  227. and if GNU Binutils support <a href="https://sourceware.org/PR21683">PR21683</a><!-- /@w -->.
  228. </p>
  229. </dd>
  230. <dt><code>-mint8</code></dt>
  231. <dd><a name="index-mint8"></a>
  232. <p>Assume <code>int</code> to be 8-bit integer. This affects the sizes of all types: a
  233. <code>char</code> is 1 byte, an <code>int</code> is 1 byte, a <code>long</code> is 2 bytes,
  234. and <code>long long</code> is 4 bytes. Please note that this option does not
  235. conform to the C standards, but it results in smaller code
  236. size.
  237. </p>
  238. </dd>
  239. <dt><code>-mmain-is-OS_task</code></dt>
  240. <dd><a name="index-mmain_002dis_002dOS_005ftask"></a>
  241. <p>Do not save registers in <code>main</code>. The effect is the same like
  242. attaching attribute <a href="AVR-Function-Attributes.html#AVR-Function-Attributes"><code>OS_task</code></a>
  243. to <code>main</code>. It is activated per default if optimization is on.
  244. </p>
  245. </dd>
  246. <dt><code>-mn-flash=<var>num</var></code></dt>
  247. <dd><a name="index-mn_002dflash"></a>
  248. <p>Assume that the flash memory has a size of
  249. <var>num</var> times 64&nbsp;KiB.
  250. </p>
  251. </dd>
  252. <dt><code>-mno-interrupts</code></dt>
  253. <dd><a name="index-mno_002dinterrupts"></a>
  254. <p>Generated code is not compatible with hardware interrupts.
  255. Code size is smaller.
  256. </p>
  257. </dd>
  258. <dt><code>-mrelax</code></dt>
  259. <dd><a name="index-mrelax"></a>
  260. <p>Try to replace <code>CALL</code> resp. <code>JMP</code> instruction by the shorter
  261. <code>RCALL</code> resp. <code>RJMP</code> instruction if applicable.
  262. Setting <samp>-mrelax</samp> just adds the <samp>--mlink-relax</samp> option to
  263. the assembler&rsquo;s command line and the <samp>--relax</samp> option to the
  264. linker&rsquo;s command line.
  265. </p>
  266. <p>Jump relaxing is performed by the linker because jump offsets are not
  267. known before code is located. Therefore, the assembler code generated by the
  268. compiler is the same, but the instructions in the executable may
  269. differ from instructions in the assembler code.
  270. </p>
  271. <p>Relaxing must be turned on if linker stubs are needed, see the
  272. section on <code>EIND</code> and linker stubs below.
  273. </p>
  274. </dd>
  275. <dt><code>-mrmw</code></dt>
  276. <dd><a name="index-mrmw"></a>
  277. <p>Assume that the device supports the Read-Modify-Write
  278. instructions <code>XCH</code>, <code>LAC</code>, <code>LAS</code> and <code>LAT</code>.
  279. </p>
  280. </dd>
  281. <dt><code>-mshort-calls</code></dt>
  282. <dd><a name="index-mshort_002dcalls"></a>
  283. <p>Assume that <code>RJMP</code> and <code>RCALL</code> can target the whole
  284. program memory.
  285. </p>
  286. <p>This option is used internally for multilib selection. It is
  287. not an optimization option, and you don&rsquo;t need to set it by hand.
  288. </p>
  289. </dd>
  290. <dt><code>-msp8</code></dt>
  291. <dd><a name="index-msp8"></a>
  292. <p>Treat the stack pointer register as an 8-bit register,
  293. i.e. assume the high byte of the stack pointer is zero.
  294. In general, you don&rsquo;t need to set this option by hand.
  295. </p>
  296. <p>This option is used internally by the compiler to select and
  297. build multilibs for architectures <code>avr2</code> and <code>avr25</code>.
  298. These architectures mix devices with and without <code>SPH</code>.
  299. For any setting other than <samp>-mmcu=avr2</samp> or <samp>-mmcu=avr25</samp>
  300. the compiler driver adds or removes this option from the compiler
  301. proper&rsquo;s command line, because the compiler then knows if the device
  302. or architecture has an 8-bit stack pointer and thus no <code>SPH</code>
  303. register or not.
  304. </p>
  305. </dd>
  306. <dt><code>-mstrict-X</code></dt>
  307. <dd><a name="index-mstrict_002dX"></a>
  308. <p>Use address register <code>X</code> in a way proposed by the hardware. This means
  309. that <code>X</code> is only used in indirect, post-increment or
  310. pre-decrement addressing.
  311. </p>
  312. <p>Without this option, the <code>X</code> register may be used in the same way
  313. as <code>Y</code> or <code>Z</code> which then is emulated by additional
  314. instructions.
  315. For example, loading a value with <code>X+const</code> addressing with a
  316. small non-negative <code>const &lt; 64</code> to a register <var>Rn</var> is
  317. performed as
  318. </p>
  319. <div class="example">
  320. <pre class="example">adiw r26, const ; X += const
  321. ld <var>Rn</var>, X ; <var>Rn</var> = *X
  322. sbiw r26, const ; X -= const
  323. </pre></div>
  324. </dd>
  325. <dt><code>-mtiny-stack</code></dt>
  326. <dd><a name="index-mtiny_002dstack"></a>
  327. <p>Only change the lower 8&nbsp;bits of the stack pointer.
  328. </p>
  329. </dd>
  330. <dt><code>-mfract-convert-truncate</code></dt>
  331. <dd><a name="index-mfract_002dconvert_002dtruncate"></a>
  332. <p>Allow to use truncation instead of rounding towards zero for fractional fixed-point types.
  333. </p>
  334. </dd>
  335. <dt><code>-nodevicelib</code></dt>
  336. <dd><a name="index-nodevicelib"></a>
  337. <p>Don&rsquo;t link against AVR-LibC&rsquo;s device specific library <code>lib&lt;mcu&gt;.a</code>.
  338. </p>
  339. </dd>
  340. <dt><code>-nodevicespecs</code></dt>
  341. <dd><a name="index-nodevicespecs"></a>
  342. <p>Don&rsquo;t add <samp>-specs=device-specs/specs-<var>mcu</var></samp> to the compiler driver&rsquo;s
  343. command line. The user takes responsibility for supplying the sub-processes
  344. like compiler proper, assembler and linker with appropriate command line
  345. options. This means that the user has to supply her private device specs
  346. file by means of <samp>-specs=<var>path-to-specs-file</var></samp>. There is no
  347. more need for option <samp>-mmcu=<var>mcu</var></samp>.
  348. </p>
  349. <p>This option can also serve as a replacement for the older way of
  350. specifying custom device-specs files that needed <samp>-B <var>some-path</var></samp> to point to a directory
  351. which contains a folder named <code>device-specs</code> which contains a specs file named
  352. <code>specs-<var>mcu</var></code>, where <var>mcu</var> was specified by <samp>-mmcu=<var>mcu</var></samp>.
  353. </p>
  354. </dd>
  355. <dt><code>-Waddr-space-convert</code></dt>
  356. <dd><a name="index-Waddr_002dspace_002dconvert"></a>
  357. <a name="index-Wno_002daddr_002dspace_002dconvert"></a>
  358. <p>Warn about conversions between address spaces in the case where the
  359. resulting address space is not contained in the incoming address space.
  360. </p>
  361. </dd>
  362. <dt><code>-Wmisspelled-isr</code></dt>
  363. <dd><a name="index-Wmisspelled_002disr"></a>
  364. <a name="index-Wno_002dmisspelled_002disr"></a>
  365. <p>Warn if the ISR is misspelled, i.e. without __vector prefix.
  366. Enabled by default.
  367. </p></dd>
  368. </dl>
  369. <a name="EIND-and-Devices-with-More-Than-128-Ki-Bytes-of-Flash"></a>
  370. <h4 class="subsubsection">3.19.6.1 <code>EIND</code> and Devices with More Than 128 Ki Bytes of Flash</h4>
  371. <a name="index-EIND"></a>
  372. <p>Pointers in the implementation are 16&nbsp;bits wide.
  373. The address of a function or label is represented as word address so
  374. that indirect jumps and calls can target any code address in the
  375. range of 64&nbsp;Ki words.
  376. </p>
  377. <p>In order to facilitate indirect jump on devices with more than 128&nbsp;Ki
  378. bytes of program memory space, there is a special function register called
  379. <code>EIND</code> that serves as most significant part of the target address
  380. when <code>EICALL</code> or <code>EIJMP</code> instructions are used.
  381. </p>
  382. <p>Indirect jumps and calls on these devices are handled as follows by
  383. the compiler and are subject to some limitations:
  384. </p>
  385. <ul>
  386. <li> The compiler never sets <code>EIND</code>.
  387. </li><li> The compiler uses <code>EIND</code> implicitly in <code>EICALL</code>/<code>EIJMP</code>
  388. instructions or might read <code>EIND</code> directly in order to emulate an
  389. indirect call/jump by means of a <code>RET</code> instruction.
  390. </li><li> The compiler assumes that <code>EIND</code> never changes during the startup
  391. code or during the application. In particular, <code>EIND</code> is not
  392. saved/restored in function or interrupt service routine
  393. prologue/epilogue.
  394. </li><li> For indirect calls to functions and computed goto, the linker
  395. generates <em>stubs</em>. Stubs are jump pads sometimes also called
  396. <em>trampolines</em>. Thus, the indirect call/jump jumps to such a stub.
  397. The stub contains a direct jump to the desired address.
  398. </li><li> Linker relaxation must be turned on so that the linker generates
  399. the stubs correctly in all situations. See the compiler option
  400. <samp>-mrelax</samp> and the linker option <samp>--relax</samp>.
  401. There are corner cases where the linker is supposed to generate stubs
  402. but aborts without relaxation and without a helpful error message.
  403. </li><li> The default linker script is arranged for code with <code>EIND = 0</code>.
  404. If code is supposed to work for a setup with <code>EIND != 0</code>, a custom
  405. linker script has to be used in order to place the sections whose
  406. name start with <code>.trampolines</code> into the segment where <code>EIND</code>
  407. points to.
  408. </li><li> The startup code from libgcc never sets <code>EIND</code>.
  409. Notice that startup code is a blend of code from libgcc and AVR-LibC.
  410. For the impact of AVR-LibC on <code>EIND</code>, see the
  411. <a href="http://nongnu.org/avr-libc/user-manual/"><span class="nolinebreak">AVR-LibC</span>&nbsp;user&nbsp;manual</a><!-- /@w -->.
  412. </li><li> It is legitimate for user-specific startup code to set up <code>EIND</code>
  413. early, for example by means of initialization code located in
  414. section <code>.init3</code>. Such code runs prior to general startup code
  415. that initializes RAM and calls constructors, but after the bit
  416. of startup code from AVR-LibC that sets <code>EIND</code> to the segment
  417. where the vector table is located.
  418. <div class="example">
  419. <pre class="example">#include &lt;avr/io.h&gt;
  420. static void
  421. __attribute__((section(&quot;.init3&quot;),naked,used,no_instrument_function))
  422. init3_set_eind (void)
  423. {
  424. __asm volatile (&quot;ldi r24,pm_hh8(__trampolines_start)\n\t&quot;
  425. &quot;out %i0,r24&quot; :: &quot;n&quot; (&amp;EIND) : &quot;r24&quot;,&quot;memory&quot;);
  426. }
  427. </pre></div>
  428. <p>The <code>__trampolines_start</code> symbol is defined in the linker script.
  429. </p>
  430. </li><li> Stubs are generated automatically by the linker if
  431. the following two conditions are met:
  432. <ul class="no-bullet">
  433. <li>- The address of a label is taken by means of the <code>gs</code> modifier
  434. (short for <em>generate stubs</em>) like so:
  435. <div class="example">
  436. <pre class="example">LDI r24, lo8(gs(<var>func</var>))
  437. LDI r25, hi8(gs(<var>func</var>))
  438. </pre></div>
  439. </li><li>- The final location of that label is in a code segment
  440. <em>outside</em> the segment where the stubs are located.
  441. </li></ul>
  442. </li><li> The compiler emits such <code>gs</code> modifiers for code labels in the
  443. following situations:
  444. <ul class="no-bullet">
  445. <li>- Taking address of a function or code label.
  446. </li><li>- Computed goto.
  447. </li><li>- If prologue-save function is used, see <samp>-mcall-prologues</samp>
  448. command-line option.
  449. </li><li>- Switch/case dispatch tables. If you do not want such dispatch
  450. tables you can specify the <samp>-fno-jump-tables</samp> command-line option.
  451. </li><li>- C and C++ constructors/destructors called during startup/shutdown.
  452. </li><li>- If the tools hit a <code>gs()</code> modifier explained above.
  453. </li></ul>
  454. </li><li> Jumping to non-symbolic addresses like so is <em>not</em> supported:
  455. <div class="example">
  456. <pre class="example">int main (void)
  457. {
  458. /* Call function at word address 0x2 */
  459. return ((int(*)(void)) 0x2)();
  460. }
  461. </pre></div>
  462. <p>Instead, a stub has to be set up, i.e. the function has to be called
  463. through a symbol (<code>func_4</code> in the example):
  464. </p>
  465. <div class="example">
  466. <pre class="example">int main (void)
  467. {
  468. extern int func_4 (void);
  469. /* Call function at byte address 0x4 */
  470. return func_4();
  471. }
  472. </pre></div>
  473. <p>and the application be linked with <samp>-Wl,--defsym,func_4=0x4</samp>.
  474. Alternatively, <code>func_4</code> can be defined in the linker script.
  475. </p></li></ul>
  476. <a name="Handling-of-the-RAMPD_002c-RAMPX_002c-RAMPY-and-RAMPZ-Special-Function-Registers"></a>
  477. <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>
  478. <a name="index-RAMPD"></a>
  479. <a name="index-RAMPX"></a>
  480. <a name="index-RAMPY"></a>
  481. <a name="index-RAMPZ"></a>
  482. <p>Some AVR devices support memories larger than the 64&nbsp;KiB range
  483. that can be accessed with 16-bit pointers. To access memory locations
  484. outside this 64&nbsp;KiB range, the content of a <code>RAMP</code>
  485. register is used as high part of the address:
  486. The <code>X</code>, <code>Y</code>, <code>Z</code> address register is concatenated
  487. with the <code>RAMPX</code>, <code>RAMPY</code>, <code>RAMPZ</code> special function
  488. register, respectively, to get a wide address. Similarly,
  489. <code>RAMPD</code> is used together with direct addressing.
  490. </p>
  491. <ul>
  492. <li> The startup code initializes the <code>RAMP</code> special function
  493. registers with zero.
  494. </li><li> If a <a href="Named-Address-Spaces.html#AVR-Named-Address-Spaces">named address space</a> other than
  495. generic or <code>__flash</code> is used, then <code>RAMPZ</code> is set
  496. as needed before the operation.
  497. </li><li> If the device supports RAM larger than 64&nbsp;KiB and the compiler
  498. needs to change <code>RAMPZ</code> to accomplish an operation, <code>RAMPZ</code>
  499. is reset to zero after the operation.
  500. </li><li> If the device comes with a specific <code>RAMP</code> register, the ISR
  501. prologue/epilogue saves/restores that SFR and initializes it with
  502. zero in case the ISR code might (implicitly) use it.
  503. </li><li> RAM larger than 64&nbsp;KiB is not supported by GCC for AVR targets.
  504. If you use inline assembler to read from locations outside the
  505. 16-bit address range and change one of the <code>RAMP</code> registers,
  506. you must reset it to zero after the access.
  507. </li></ul>
  508. <a name="AVR-Built_002din-Macros"></a>
  509. <h4 class="subsubsection">3.19.6.3 AVR Built-in Macros</h4>
  510. <p>GCC defines several built-in macros so that the user code can test
  511. for the presence or absence of features. Almost any of the following
  512. built-in macros are deduced from device capabilities and thus
  513. triggered by the <samp>-mmcu=</samp> command-line option.
  514. </p>
  515. <p>For even more AVR-specific built-in macros see
  516. <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>.
  517. </p>
  518. <dl compact="compact">
  519. <dt><code>__AVR_ARCH__</code></dt>
  520. <dd><p>Build-in macro that resolves to a decimal number that identifies the
  521. architecture and depends on the <samp>-mmcu=<var>mcu</var></samp> option.
  522. Possible values are:
  523. </p>
  524. <p><code>2</code>, <code>25</code>, <code>3</code>, <code>31</code>, <code>35</code>,
  525. <code>4</code>, <code>5</code>, <code>51</code>, <code>6</code>
  526. </p>
  527. <p>for <var>mcu</var>=<code>avr2</code>, <code>avr25</code>, <code>avr3</code>, <code>avr31</code>,
  528. <code>avr35</code>, <code>avr4</code>, <code>avr5</code>, <code>avr51</code>, <code>avr6</code>,
  529. </p>
  530. <p>respectively and
  531. </p>
  532. <p><code>100</code>,
  533. <code>102</code>, <code>103</code>, <code>104</code>,
  534. <code>105</code>, <code>106</code>, <code>107</code>
  535. </p>
  536. <p>for <var>mcu</var>=<code>avrtiny</code>,
  537. <code>avrxmega2</code>, <code>avrxmega3</code>, <code>avrxmega4</code>,
  538. <code>avrxmega5</code>, <code>avrxmega6</code>, <code>avrxmega7</code>, respectively.
  539. If <var>mcu</var> specifies a device, this built-in macro is set
  540. accordingly. For example, with <samp>-mmcu=atmega8</samp> the macro is
  541. defined to <code>4</code>.
  542. </p>
  543. </dd>
  544. <dt><code>__AVR_<var>Device</var>__</code></dt>
  545. <dd><p>Setting <samp>-mmcu=<var>device</var></samp> defines this built-in macro which reflects
  546. the device&rsquo;s name. For example, <samp>-mmcu=atmega8</samp> defines the
  547. built-in macro <code>__AVR_ATmega8__</code>, <samp>-mmcu=attiny261a</samp> defines
  548. <code>__AVR_ATtiny261A__</code>, etc.
  549. </p>
  550. <p>The built-in macros&rsquo; names follow
  551. the scheme <code>__AVR_<var>Device</var>__</code> where <var>Device</var> is
  552. the device name as from the AVR user manual. The difference between
  553. <var>Device</var> in the built-in macro and <var>device</var> in
  554. <samp>-mmcu=<var>device</var></samp> is that the latter is always lowercase.
  555. </p>
  556. <p>If <var>device</var> is not a device but only a core architecture like
  557. &lsquo;<samp>avr51</samp>&rsquo;, this macro is not defined.
  558. </p>
  559. </dd>
  560. <dt><code>__AVR_DEVICE_NAME__</code></dt>
  561. <dd><p>Setting <samp>-mmcu=<var>device</var></samp> defines this built-in macro to
  562. the device&rsquo;s name. For example, with <samp>-mmcu=atmega8</samp> the macro
  563. is defined to <code>atmega8</code>.
  564. </p>
  565. <p>If <var>device</var> is not a device but only a core architecture like
  566. &lsquo;<samp>avr51</samp>&rsquo;, this macro is not defined.
  567. </p>
  568. </dd>
  569. <dt><code>__AVR_XMEGA__</code></dt>
  570. <dd><p>The device / architecture belongs to the XMEGA family of devices.
  571. </p>
  572. </dd>
  573. <dt><code>__AVR_HAVE_ELPM__</code></dt>
  574. <dd><p>The device has the <code>ELPM</code> instruction.
  575. </p>
  576. </dd>
  577. <dt><code>__AVR_HAVE_ELPMX__</code></dt>
  578. <dd><p>The device has the <code>ELPM R<var>n</var>,Z</code> and <code>ELPM
  579. R<var>n</var>,Z+</code> instructions.
  580. </p>
  581. </dd>
  582. <dt><code>__AVR_HAVE_MOVW__</code></dt>
  583. <dd><p>The device has the <code>MOVW</code> instruction to perform 16-bit
  584. register-register moves.
  585. </p>
  586. </dd>
  587. <dt><code>__AVR_HAVE_LPMX__</code></dt>
  588. <dd><p>The device has the <code>LPM R<var>n</var>,Z</code> and
  589. <code>LPM R<var>n</var>,Z+</code> instructions.
  590. </p>
  591. </dd>
  592. <dt><code>__AVR_HAVE_MUL__</code></dt>
  593. <dd><p>The device has a hardware multiplier.
  594. </p>
  595. </dd>
  596. <dt><code>__AVR_HAVE_JMP_CALL__</code></dt>
  597. <dd><p>The device has the <code>JMP</code> and <code>CALL</code> instructions.
  598. This is the case for devices with more than 8&nbsp;KiB of program
  599. memory.
  600. </p>
  601. </dd>
  602. <dt><code>__AVR_HAVE_EIJMP_EICALL__</code></dt>
  603. <dt><code>__AVR_3_BYTE_PC__</code></dt>
  604. <dd><p>The device has the <code>EIJMP</code> and <code>EICALL</code> instructions.
  605. This is the case for devices with more than 128&nbsp;KiB of program memory.
  606. This also means that the program counter
  607. (PC) is 3&nbsp;bytes wide.
  608. </p>
  609. </dd>
  610. <dt><code>__AVR_2_BYTE_PC__</code></dt>
  611. <dd><p>The program counter (PC) is 2&nbsp;bytes wide. This is the case for devices
  612. with up to 128&nbsp;KiB of program memory.
  613. </p>
  614. </dd>
  615. <dt><code>__AVR_HAVE_8BIT_SP__</code></dt>
  616. <dt><code>__AVR_HAVE_16BIT_SP__</code></dt>
  617. <dd><p>The stack pointer (SP) register is treated as 8-bit respectively
  618. 16-bit register by the compiler.
  619. The definition of these macros is affected by <samp>-mtiny-stack</samp>.
  620. </p>
  621. </dd>
  622. <dt><code>__AVR_HAVE_SPH__</code></dt>
  623. <dt><code>__AVR_SP8__</code></dt>
  624. <dd><p>The device has the SPH (high part of stack pointer) special function
  625. register or has an 8-bit stack pointer, respectively.
  626. The definition of these macros is affected by <samp>-mmcu=</samp> and
  627. in the cases of <samp>-mmcu=avr2</samp> and <samp>-mmcu=avr25</samp> also
  628. by <samp>-msp8</samp>.
  629. </p>
  630. </dd>
  631. <dt><code>__AVR_HAVE_RAMPD__</code></dt>
  632. <dt><code>__AVR_HAVE_RAMPX__</code></dt>
  633. <dt><code>__AVR_HAVE_RAMPY__</code></dt>
  634. <dt><code>__AVR_HAVE_RAMPZ__</code></dt>
  635. <dd><p>The device has the <code>RAMPD</code>, <code>RAMPX</code>, <code>RAMPY</code>,
  636. <code>RAMPZ</code> special function register, respectively.
  637. </p>
  638. </dd>
  639. <dt><code>__NO_INTERRUPTS__</code></dt>
  640. <dd><p>This macro reflects the <samp>-mno-interrupts</samp> command-line option.
  641. </p>
  642. </dd>
  643. <dt><code>__AVR_ERRATA_SKIP__</code></dt>
  644. <dt><code>__AVR_ERRATA_SKIP_JMP_CALL__</code></dt>
  645. <dd><p>Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit
  646. instructions because of a hardware erratum. Skip instructions are
  647. <code>SBRS</code>, <code>SBRC</code>, <code>SBIS</code>, <code>SBIC</code> and <code>CPSE</code>.
  648. The second macro is only defined if <code>__AVR_HAVE_JMP_CALL__</code> is also
  649. set.
  650. </p>
  651. </dd>
  652. <dt><code>__AVR_ISA_RMW__</code></dt>
  653. <dd><p>The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT).
  654. </p>
  655. </dd>
  656. <dt><code>__AVR_SFR_OFFSET__=<var>offset</var></code></dt>
  657. <dd><p>Instructions that can address I/O special function registers directly
  658. like <code>IN</code>, <code>OUT</code>, <code>SBI</code>, etc. may use a different
  659. address as if addressed by an instruction to access RAM like <code>LD</code>
  660. or <code>STS</code>. This offset depends on the device architecture and has
  661. to be subtracted from the RAM address in order to get the
  662. respective I/O&nbsp;address.
  663. </p>
  664. </dd>
  665. <dt><code>__AVR_SHORT_CALLS__</code></dt>
  666. <dd><p>The <samp>-mshort-calls</samp> command line option is set.
  667. </p>
  668. </dd>
  669. <dt><code>__AVR_PM_BASE_ADDRESS__=<var>addr</var></code></dt>
  670. <dd><p>Some devices support reading from flash memory by means of <code>LD*</code>
  671. instructions. The flash memory is seen in the data address space
  672. at an offset of <code>__AVR_PM_BASE_ADDRESS__</code>. If this macro
  673. is not defined, this feature is not available. If defined,
  674. the address space is linear and there is no need to put
  675. <code>.rodata</code> into RAM. This is handled by the default linker
  676. description file, and is currently available for
  677. <code>avrtiny</code> and <code>avrxmega3</code>. Even more convenient,
  678. there is no need to use address spaces like <code>__flash</code> or
  679. features like attribute <code>progmem</code> and <code>pgm_read_*</code>.
  680. </p>
  681. </dd>
  682. <dt><code>__WITH_AVRLIBC__</code></dt>
  683. <dd><p>The compiler is configured to be used together with AVR-Libc.
  684. See the <samp>--with-avrlibc</samp> configure option.
  685. </p>
  686. </dd>
  687. <dt><code>__HAVE_DOUBLE_MULTILIB__</code></dt>
  688. <dd><p>Defined if <samp>-mdouble=</samp> acts as a multilib option.
  689. </p>
  690. </dd>
  691. <dt><code>__HAVE_DOUBLE32__</code></dt>
  692. <dt><code>__HAVE_DOUBLE64__</code></dt>
  693. <dd><p>Defined if the compiler supports 32-bit double resp. 64-bit double.
  694. The actual layout is specified by option <samp>-mdouble=</samp>.
  695. </p>
  696. </dd>
  697. <dt><code>__DEFAULT_DOUBLE__</code></dt>
  698. <dd><p>The size in bits of <code>double</code> if <samp>-mdouble=</samp> is not set.
  699. To test the layout of <code>double</code> in a program, use the built-in
  700. macro <code>__SIZEOF_DOUBLE__</code>.
  701. </p>
  702. </dd>
  703. <dt><code>__HAVE_LONG_DOUBLE32__</code></dt>
  704. <dt><code>__HAVE_LONG_DOUBLE64__</code></dt>
  705. <dt><code>__HAVE_LONG_DOUBLE_MULTILIB__</code></dt>
  706. <dt><code>__DEFAULT_LONG_DOUBLE__</code></dt>
  707. <dd><p>Same as above, but for <code>long double</code> instead of <code>double</code>.
  708. </p>
  709. </dd>
  710. <dt><code>__WITH_DOUBLE_COMPARISON__</code></dt>
  711. <dd><p>Reflects the <code>--with-double-comparison={tristate|bool|libf7}</code>
  712. <a href="https://gcc.gnu.org/install/configure.html#avr">configure&nbsp;option</a><!-- /@w -->
  713. and is defined to <code>2</code> or <code>3</code>.
  714. </p>
  715. </dd>
  716. <dt><code>__WITH_LIBF7_LIBGCC__</code></dt>
  717. <dt><code>__WITH_LIBF7_MATH__</code></dt>
  718. <dt><code>__WITH_LIBF7_MATH_SYMBOLS__</code></dt>
  719. <dd><p>Reflects the <code>--with-libf7={libgcc|math|math-symbols}</code>
  720. <a href="https://gcc.gnu.org/install/configure.html#avr">configure&nbsp;option</a><!-- /@w -->.
  721. </p>
  722. </dd>
  723. </dl>
  724. <hr>
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