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diff --git a/share/doc/gcc/AVR-Options.html b/share/doc/gcc/AVR-Options.html new file mode 100644 index 0000000..2696b80 --- /dev/null +++ b/share/doc/gcc/AVR-Options.html @@ -0,0 +1,779 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> +<html> +<!-- This file documents the use of the GNU compilers. + +Copyright (C) 1988-2023 Free Software Foundation, Inc. + +Permission is granted to copy, distribute and/or modify this document +under the terms of the GNU Free Documentation License, Version 1.3 or +any later version published by the Free Software Foundation; with the +Invariant Sections being "Funding Free Software", the Front-Cover +Texts being (a) (see below), and with the Back-Cover Texts being (b) +(see below). A copy of the license is included in the section entitled +"GNU Free Documentation License". + +(a) The FSF's Front-Cover Text is: + +A GNU Manual + +(b) The FSF's Back-Cover Text is: + +You have freedom to copy and modify this GNU Manual, like GNU + software. 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name="index-mmcu"></a> +</dd> +<dt><code>-mmcu=<var>mcu</var></code></dt> +<dd><p>Specify Atmel AVR instruction set architectures (ISA) or MCU type. +</p> +<p>The default for this option is ‘<samp>avr2</samp>’. +</p> +<p>GCC supports the following AVR devices and ISAs: +</p> + + + +<dl compact="compact"> +<dt><code>avr2</code></dt> +<dd><p>“Classic” devices with up to 8 KiB of program memory. +<br><var>mcu</var> = <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>. +</p> +</dd> +<dt><code>avr25</code></dt> +<dd><p>“Classic” devices with up to 8 KiB of program memory and with the <code>MOVW</code> instruction. +<br><var>mcu</var> = <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>. +</p> +</dd> +<dt><code>avr3</code></dt> +<dd><p>“Classic” devices with 16 KiB up to 64 KiB of program memory. +<br><var>mcu</var> = <code>at76c711</code>, <code>at43usb355</code>. +</p> +</dd> +<dt><code>avr31</code></dt> +<dd><p>“Classic” devices with 128 KiB of program memory. +<br><var>mcu</var> = <code>atmega103</code>, <code>at43usb320</code>. +</p> +</dd> +<dt><code>avr35</code></dt> +<dd><p>“Classic” devices with 16 KiB up to 64 KiB of program memory and with the <code>MOVW</code> instruction. +<br><var>mcu</var> = <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>. +</p> +</dd> +<dt><code>avr4</code></dt> +<dd><p>“Enhanced” devices with up to 8 KiB of program memory. +<br><var>mcu</var> = <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>. +</p> +</dd> +<dt><code>avr5</code></dt> +<dd><p>“Enhanced” devices with 16 KiB up to 64 KiB of program memory. +<br><var>mcu</var> = <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>atmega324pb</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>. +</p> +</dd> +<dt><code>avr51</code></dt> +<dd><p>“Enhanced” devices with 128 KiB of program memory. +<br><var>mcu</var> = <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>. +</p> +</dd> +<dt><code>avr6</code></dt> +<dd><p>“Enhanced” devices with 3-byte PC, i.e. with more than 128 KiB of program memory. +<br><var>mcu</var> = <code>atmega256rfr2</code>, <code>atmega2560</code>, <code>atmega2561</code>, <code>atmega2564rfr2</code>. +</p> +</dd> +<dt><code>avrxmega2</code></dt> +<dd><p>“XMEGA” devices with more than 8 KiB and up to 64 KiB of program memory. +<br><var>mcu</var> = <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>, <code>avr64da28</code>, <code>avr64da32</code>, <code>avr64da48</code>, <code>avr64da64</code>, <code>avr64db28</code>, <code>avr64db32</code>, <code>avr64db48</code>, <code>avr64db64</code>, <code>avr64dd14</code>, <code>avr64dd20</code>, <code>avr64dd28</code>, <code>avr64dd32</code>, <code>avr64ea28</code>, <code>avr64ea32</code>, <code>avr64ea48</code>. +</p> +</dd> +<dt><code>avrxmega3</code></dt> +<dd><p>“XMEGA” devices with up to 64 KiB of combined program memory and RAM, and with program memory visible in the RAM address space. +<br><var>mcu</var> = <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>attiny424</code>, <code>attiny426</code>, <code>attiny427</code>, <code>attiny804</code>, <code>attiny806</code>, <code>attiny807</code>, <code>attiny814</code>, <code>attiny816</code>, <code>attiny817</code>, <code>attiny824</code>, <code>attiny826</code>, <code>attiny827</code>, <code>attiny1604</code>, <code>attiny1606</code>, <code>attiny1607</code>, <code>attiny1614</code>, <code>attiny1616</code>, <code>attiny1617</code>, <code>attiny1624</code>, <code>attiny1626</code>, <code>attiny1627</code>, <code>attiny3214</code>, <code>attiny3216</code>, <code>attiny3217</code>, <code>attiny3224</code>, <code>attiny3226</code>, <code>attiny3227</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>, <code>avr16dd14</code>, <code>avr16dd20</code>, <code>avr16dd28</code>, <code>avr16dd32</code>, <code>avr32da28</code>, <code>avr32da32</code>, <code>avr32da48</code>, <code>avr32db28</code>, <code>avr32db32</code>, <code>avr32db48</code>, <code>avr32dd14</code>, <code>avr32dd20</code>, <code>avr32dd28</code>, <code>avr32dd32</code>. +</p> +</dd> +<dt><code>avrxmega4</code></dt> +<dd><p>“XMEGA” devices with more than 64 KiB and up to 128 KiB of program memory. +<br><var>mcu</var> = <code>atxmega64a3</code>, <code>atxmega64a3u</code>, <code>atxmega64a4u</code>, <code>atxmega64b1</code>, <code>atxmega64b3</code>, <code>atxmega64c3</code>, <code>atxmega64d3</code>, <code>atxmega64d4</code>, <code>avr128da28</code>, <code>avr128da32</code>, <code>avr128da48</code>, <code>avr128da64</code>, <code>avr128db28</code>, <code>avr128db32</code>, <code>avr128db48</code>, <code>avr128db64</code>. +</p> +</dd> +<dt><code>avrxmega5</code></dt> +<dd><p>“XMEGA” devices with more than 64 KiB and up to 128 KiB of program memory and more than 64 KiB of RAM. +<br><var>mcu</var> = <code>atxmega64a1</code>, <code>atxmega64a1u</code>. +</p> +</dd> +<dt><code>avrxmega6</code></dt> +<dd><p>“XMEGA” devices with more than 128 KiB of program memory. +<br><var>mcu</var> = <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>. +</p> +</dd> +<dt><code>avrxmega7</code></dt> +<dd><p>“XMEGA” devices with more than 128 KiB of program memory and more than 64 KiB of RAM. +<br><var>mcu</var> = <code>atxmega128a1</code>, <code>atxmega128a1u</code>, <code>atxmega128a4u</code>. +</p> +</dd> +<dt><code>avrtiny</code></dt> +<dd><p>“TINY” Tiny core devices with 512 B up to 4 KiB of program memory. +<br><var>mcu</var> = <code>attiny4</code>, <code>attiny5</code>, <code>attiny9</code>, <code>attiny10</code>, <code>attiny102</code>, <code>attiny104</code>, <code>attiny20</code>, <code>attiny40</code>. +</p> +</dd> +<dt><code>avr1</code></dt> +<dd><p>This ISA is implemented by the minimal AVR core and supported for assembler only. +<br><var>mcu</var> = <code>attiny11</code>, <code>attiny12</code>, <code>attiny15</code>, <code>attiny28</code>, <code>at90s1200</code>. +</p> +</dd> +</dl> + +<a name="index-mabsdata"></a> +</dd> +<dt><code>-mabsdata</code></dt> +<dd> +<p>Assume that all data in static storage can be accessed by LDS / STS +instructions. This option has only an effect on reduced Tiny devices like +ATtiny40. See also the <code>absdata</code> +<a href="AVR-Variable-Attributes.html#AVR-Variable-Attributes">variable attribute</a>. +</p> +<a name="index-maccumulate_002dargs"></a> +</dd> +<dt><code>-maccumulate-args</code></dt> +<dd><p>Accumulate outgoing function arguments and acquire/release the needed +stack space for outgoing function arguments once in function +prologue/epilogue. Without this option, outgoing arguments are pushed +before calling a function and popped afterwards. +</p> +<p>Popping the arguments after the function call can be expensive on +AVR so that accumulating the stack space might lead to smaller +executables because arguments need not be removed from the +stack after such a function call. +</p> +<p>This option can lead to reduced code size for functions that perform +several calls to functions that get their arguments on the stack like +calls to printf-like functions. +</p> +<a name="index-mbranch_002dcost-1"></a> +</dd> +<dt><code>-mbranch-cost=<var>cost</var></code></dt> +<dd><p>Set the branch costs for conditional branch instructions to +<var>cost</var>. Reasonable values for <var>cost</var> are small, non-negative +integers. The default branch cost is 0. +</p> +<a name="index-mcall_002dprologues"></a> +</dd> +<dt><code>-mcall-prologues</code></dt> +<dd><p>Functions prologues/epilogues are expanded as calls to appropriate +subroutines. Code size is smaller. +</p> +<a name="index-mdouble"></a> +<a name="index-mlong_002ddouble"></a> +</dd> +<dt><code>-mdouble=<var>bits</var></code></dt> +<dt><code>-mlong-double=<var>bits</var></code></dt> +<dd><p>Set the size (in bits) of the <code>double</code> or <code>long double</code> type, +respectively. Possible values for <var>bits</var> are 32 and 64. +Whether or not a specific value for <var>bits</var> is allowed depends on +the <code>--with-double=</code> and <code>--with-long-double=</code> +<a href="https://gcc.gnu.org/install/configure.html#avr">configure options</a><!-- /@w -->, +and the same applies for the default values of the options. +</p> +<a name="index-mgas_002disr_002dprologues"></a> +</dd> +<dt><code>-mgas-isr-prologues</code></dt> +<dd><p>Interrupt service routines (ISRs) may use the <code>__gcc_isr</code> pseudo +instruction supported by GNU Binutils. +If this option is on, the feature can still be disabled for individual +ISRs by means of the <a href="AVR-Function-Attributes.html#AVR-Function-Attributes"><code>no_gccisr</code></a> +function attribute. This feature is activated per default +if optimization is on (but not with <samp>-Og</samp>, see <a href="Optimize-Options.html#Optimize-Options">Optimize Options</a>), +and if GNU Binutils support <a href="https://sourceware.org/PR21683">PR21683</a><!-- /@w -->. +</p> +<a name="index-mint8"></a> +</dd> +<dt><code>-mint8</code></dt> +<dd><p>Assume <code>int</code> to be 8-bit integer. This affects the sizes of all types: a +<code>char</code> is 1 byte, an <code>int</code> is 1 byte, a <code>long</code> is 2 bytes, +and <code>long long</code> is 4 bytes. Please note that this option does not +conform to the C standards, but it results in smaller code +size. +</p> +<a name="index-mmain_002dis_002dOS_005ftask"></a> +</dd> +<dt><code>-mmain-is-OS_task</code></dt> +<dd><p>Do not save registers in <code>main</code>. The effect is the same like +attaching attribute <a href="AVR-Function-Attributes.html#AVR-Function-Attributes"><code>OS_task</code></a> +to <code>main</code>. It is activated per default if optimization is on. +</p> +<a name="index-mn_002dflash"></a> +</dd> +<dt><code>-mn-flash=<var>num</var></code></dt> +<dd><p>Assume that the flash memory has a size of +<var>num</var> times 64 KiB. +</p> +<a name="index-mno_002dinterrupts"></a> +</dd> +<dt><code>-mno-interrupts</code></dt> +<dd><p>Generated code is not compatible with hardware interrupts. +Code size is smaller. +</p> +<a name="index-mrelax"></a> +</dd> +<dt><code>-mrelax</code></dt> +<dd><p>Try to replace <code>CALL</code> resp. <code>JMP</code> instruction by the shorter +<code>RCALL</code> resp. <code>RJMP</code> instruction if applicable. +Setting <samp>-mrelax</samp> just adds the <samp>--mlink-relax</samp> option to +the assembler’s command line and the <samp>--relax</samp> option to the +linker’s command line. +</p> +<p>Jump relaxing is performed by the linker because jump offsets are not +known before code is located. Therefore, the assembler code generated by the +compiler is the same, but the instructions in the executable may +differ from instructions in the assembler code. +</p> +<p>Relaxing must be turned on if linker stubs are needed, see the +section on <code>EIND</code> and linker stubs below. +</p> +<a name="index-mrmw"></a> +</dd> +<dt><code>-mrmw</code></dt> +<dd><p>Assume that the device supports the Read-Modify-Write +instructions <code>XCH</code>, <code>LAC</code>, <code>LAS</code> and <code>LAT</code>. +</p> +<a name="index-mshort_002dcalls"></a> +</dd> +<dt><code>-mshort-calls</code></dt> +<dd> +<p>Assume that <code>RJMP</code> and <code>RCALL</code> can target the whole +program memory. +</p> +<p>This option is used internally for multilib selection. It is +not an optimization option, and you don’t need to set it by hand. +</p> +<a name="index-msp8"></a> +</dd> +<dt><code>-msp8</code></dt> +<dd><p>Treat the stack pointer register as an 8-bit register, +i.e. assume the high byte of the stack pointer is zero. +In general, you don’t need to set this option by hand. +</p> +<p>This option is used internally by the compiler to select and +build multilibs for architectures <code>avr2</code> and <code>avr25</code>. +These architectures mix devices with and without <code>SPH</code>. +For any setting other than <samp>-mmcu=avr2</samp> or <samp>-mmcu=avr25</samp> +the compiler driver adds or removes this option from the compiler +proper’s command line, because the compiler then knows if the device +or architecture has an 8-bit stack pointer and thus no <code>SPH</code> +register or not. +</p> +<a name="index-mstrict_002dX"></a> +</dd> +<dt><code>-mstrict-X</code></dt> +<dd><p>Use address register <code>X</code> in a way proposed by the hardware. This means +that <code>X</code> is only used in indirect, post-increment or +pre-decrement addressing. +</p> +<p>Without this option, the <code>X</code> register may be used in the same way +as <code>Y</code> or <code>Z</code> which then is emulated by additional +instructions. +For example, loading a value with <code>X+const</code> addressing with a +small non-negative <code>const < 64</code> to a register <var>Rn</var> is +performed as +</p> +<div class="example"> +<pre class="example">adiw r26, const ; X += const +ld <var>Rn</var>, X ; <var>Rn</var> = *X +sbiw r26, const ; X -= const +</pre></div> + +<a name="index-mtiny_002dstack"></a> +</dd> +<dt><code>-mtiny-stack</code></dt> +<dd><p>Only change the lower 8 bits of the stack pointer. +</p> +<a name="index-mfract_002dconvert_002dtruncate"></a> +</dd> +<dt><code>-mfract-convert-truncate</code></dt> +<dd><p>Allow to use truncation instead of rounding towards zero for fractional fixed-point types. +</p> +<a name="index-nodevicelib"></a> +</dd> +<dt><code>-nodevicelib</code></dt> +<dd><p>Don’t link against AVR-LibC’s device specific library <code>lib<mcu>.a</code>. +</p> +<a name="index-nodevicespecs"></a> +</dd> +<dt><code>-nodevicespecs</code></dt> +<dd><p>Don’t add <samp>-specs=device-specs/specs-<var>mcu</var></samp> to the compiler driver’s +command line. The user takes responsibility for supplying the sub-processes +like compiler proper, assembler and linker with appropriate command line +options. This means that the user has to supply her private device specs +file by means of <samp>-specs=<var>path-to-specs-file</var></samp>. There is no +more need for option <samp>-mmcu=<var>mcu</var></samp>. +</p> +<p>This option can also serve as a replacement for the older way of +specifying custom device-specs files that needed <samp>-B <var>some-path</var></samp> to point to a directory +which contains a folder named <code>device-specs</code> which contains a specs file named +<code>specs-<var>mcu</var></code>, where <var>mcu</var> was specified by <samp>-mmcu=<var>mcu</var></samp>. +</p> +<a name="index-Waddr_002dspace_002dconvert"></a> +<a name="index-Wno_002daddr_002dspace_002dconvert"></a> +</dd> +<dt><code>-Waddr-space-convert</code></dt> +<dd><p>Warn about conversions between address spaces in the case where the +resulting address space is not contained in the incoming address space. +</p> +<a name="index-Wmisspelled_002disr"></a> +<a name="index-Wno_002dmisspelled_002disr"></a> +</dd> +<dt><code>-Wmisspelled-isr</code></dt> +<dd><p>Warn if the ISR is misspelled, i.e. without __vector prefix. +Enabled by default. +</p></dd> +</dl> + +<a name="EIND-and-Devices-with-More-Than-128-Ki-Bytes-of-Flash"></a> +<h4 class="subsubsection">3.19.6.1 <code>EIND</code> and Devices with More Than 128 Ki Bytes of Flash</h4> +<a name="index-EIND"></a> +<p>Pointers in the implementation are 16 bits wide. +The address of a function or label is represented as word address so +that indirect jumps and calls can target any code address in the +range of 64 Ki words. +</p> +<p>In order to facilitate indirect jump on devices with more than 128 Ki +bytes of program memory space, there is a special function register called +<code>EIND</code> that serves as most significant part of the target address +when <code>EICALL</code> or <code>EIJMP</code> instructions are used. +</p> +<p>Indirect jumps and calls on these devices are handled as follows by +the compiler and are subject to some limitations: +</p> +<ul> +<li> The compiler never sets <code>EIND</code>. + +</li><li> The compiler uses <code>EIND</code> implicitly in <code>EICALL</code>/<code>EIJMP</code> +instructions or might read <code>EIND</code> directly in order to emulate an +indirect call/jump by means of a <code>RET</code> instruction. + +</li><li> The compiler assumes that <code>EIND</code> never changes during the startup +code or during the application. In particular, <code>EIND</code> is not +saved/restored in function or interrupt service routine +prologue/epilogue. + +</li><li> For indirect calls to functions and computed goto, the linker +generates <em>stubs</em>. Stubs are jump pads sometimes also called +<em>trampolines</em>. Thus, the indirect call/jump jumps to such a stub. +The stub contains a direct jump to the desired address. + +</li><li> Linker relaxation must be turned on so that the linker generates +the stubs correctly in all situations. See the compiler option +<samp>-mrelax</samp> and the linker option <samp>--relax</samp>. +There are corner cases where the linker is supposed to generate stubs +but aborts without relaxation and without a helpful error message. + +</li><li> The default linker script is arranged for code with <code>EIND = 0</code>. +If code is supposed to work for a setup with <code>EIND != 0</code>, a custom +linker script has to be used in order to place the sections whose +name start with <code>.trampolines</code> into the segment where <code>EIND</code> +points to. + +</li><li> The startup code from libgcc never sets <code>EIND</code>. +Notice that startup code is a blend of code from libgcc and AVR-LibC. +For the impact of AVR-LibC on <code>EIND</code>, see the +<a href="https://www.nongnu.org/avr-libc/user-manual/"><span class="nolinebreak">AVR-LibC</span> user manual</a><!-- /@w -->. + +</li><li> It is legitimate for user-specific startup code to set up <code>EIND</code> +early, for example by means of initialization code located in +section <code>.init3</code>. Such code runs prior to general startup code +that initializes RAM and calls constructors, but after the bit +of startup code from AVR-LibC that sets <code>EIND</code> to the segment +where the vector table is located. +<div class="example"> +<pre class="example">#include <avr/io.h> + +static void +__attribute__((section(".init3"),naked,used,no_instrument_function)) +init3_set_eind (void) +{ + __asm volatile ("ldi r24,pm_hh8(__trampolines_start)\n\t" + "out %i0,r24" :: "n" (&EIND) : "r24","memory"); +} +</pre></div> + +<p>The <code>__trampolines_start</code> symbol is defined in the linker script. +</p> +</li><li> Stubs are generated automatically by the linker if +the following two conditions are met: +<ul class="no-bullet"> +<li>- The address of a label is taken by means of the <code>gs</code> modifier +(short for <em>generate stubs</em>) like so: +<div class="example"> +<pre class="example">LDI r24, lo8(gs(<var>func</var>)) +LDI r25, hi8(gs(<var>func</var>)) +</pre></div> +</li><li>- The final location of that label is in a code segment +<em>outside</em> the segment where the stubs are located. +</li></ul> + +</li><li> The compiler emits such <code>gs</code> modifiers for code labels in the +following situations: +<ul class="no-bullet"> +<li>- Taking address of a function or code label. +</li><li>- Computed goto. +</li><li>- If prologue-save function is used, see <samp>-mcall-prologues</samp> +command-line option. +</li><li>- Switch/case dispatch tables. If you do not want such dispatch +tables you can specify the <samp>-fno-jump-tables</samp> command-line option. +</li><li>- C and C++ constructors/destructors called during startup/shutdown. +</li><li>- If the tools hit a <code>gs()</code> modifier explained above. +</li></ul> + +</li><li> Jumping to non-symbolic addresses like so is <em>not</em> supported: + +<div class="example"> +<pre class="example">int main (void) +{ + /* Call function at word address 0x2 */ + return ((int(*)(void)) 0x2)(); +} +</pre></div> + +<p>Instead, a stub has to be set up, i.e. the function has to be called +through a symbol (<code>func_4</code> in the example): +</p> +<div class="example"> +<pre class="example">int main (void) +{ + extern int func_4 (void); + + /* Call function at byte address 0x4 */ + return func_4(); +} +</pre></div> + +<p>and the application be linked with <samp>-Wl,--defsym,func_4=0x4</samp>. +Alternatively, <code>func_4</code> can be defined in the linker script. +</p></li></ul> + +<a name="Handling-of-the-RAMPD_002c-RAMPX_002c-RAMPY-and-RAMPZ-Special-Function-Registers"></a> +<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> +<a name="index-RAMPD"></a> +<a name="index-RAMPX"></a> +<a name="index-RAMPY"></a> +<a name="index-RAMPZ"></a> +<p>Some AVR devices support memories larger than the 64 KiB range +that can be accessed with 16-bit pointers. To access memory locations +outside this 64 KiB range, the content of a <code>RAMP</code> +register is used as high part of the address: +The <code>X</code>, <code>Y</code>, <code>Z</code> address register is concatenated +with the <code>RAMPX</code>, <code>RAMPY</code>, <code>RAMPZ</code> special function +register, respectively, to get a wide address. Similarly, +<code>RAMPD</code> is used together with direct addressing. +</p> +<ul> +<li> The startup code initializes the <code>RAMP</code> special function +registers with zero. + +</li><li> If a <a href="Named-Address-Spaces.html#AVR-Named-Address-Spaces">named address space</a> other than +generic or <code>__flash</code> is used, then <code>RAMPZ</code> is set +as needed before the operation. + +</li><li> If the device supports RAM larger than 64 KiB and the compiler +needs to change <code>RAMPZ</code> to accomplish an operation, <code>RAMPZ</code> +is reset to zero after the operation. + +</li><li> If the device comes with a specific <code>RAMP</code> register, the ISR +prologue/epilogue saves/restores that SFR and initializes it with +zero in case the ISR code might (implicitly) use it. + +</li><li> RAM larger than 64 KiB is not supported by GCC for AVR targets. +If you use inline assembler to read from locations outside the +16-bit address range and change one of the <code>RAMP</code> registers, +you must reset it to zero after the access. + +</li></ul> + +<a name="AVR-Built_002din-Macros"></a> +<h4 class="subsubsection">3.19.6.3 AVR Built-in Macros</h4> + +<p>GCC defines several built-in macros so that the user code can test +for the presence or absence of features. Almost any of the following +built-in macros are deduced from device capabilities and thus +triggered by the <samp>-mmcu=</samp> command-line option. +</p> +<p>For even more AVR-specific built-in macros see +<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>. +</p> +<dl compact="compact"> +<dt><code>__AVR_ARCH__</code></dt> +<dd><p>Build-in macro that resolves to a decimal number that identifies the +architecture and depends on the <samp>-mmcu=<var>mcu</var></samp> option. +Possible values are: +</p> +<p><code>2</code>, <code>25</code>, <code>3</code>, <code>31</code>, <code>35</code>, +<code>4</code>, <code>5</code>, <code>51</code>, <code>6</code> +</p> +<p>for <var>mcu</var>=<code>avr2</code>, <code>avr25</code>, <code>avr3</code>, <code>avr31</code>, +<code>avr35</code>, <code>avr4</code>, <code>avr5</code>, <code>avr51</code>, <code>avr6</code>, +</p> +<p>respectively and +</p> +<p><code>100</code>, +<code>102</code>, <code>103</code>, <code>104</code>, +<code>105</code>, <code>106</code>, <code>107</code> +</p> +<p>for <var>mcu</var>=<code>avrtiny</code>, +<code>avrxmega2</code>, <code>avrxmega3</code>, <code>avrxmega4</code>, +<code>avrxmega5</code>, <code>avrxmega6</code>, <code>avrxmega7</code>, respectively. +If <var>mcu</var> specifies a device, this built-in macro is set +accordingly. For example, with <samp>-mmcu=atmega8</samp> the macro is +defined to <code>4</code>. +</p> +</dd> +<dt><code>__AVR_<var>Device</var>__</code></dt> +<dd><p>Setting <samp>-mmcu=<var>device</var></samp> defines this built-in macro which reflects +the device’s name. For example, <samp>-mmcu=atmega8</samp> defines the +built-in macro <code>__AVR_ATmega8__</code>, <samp>-mmcu=attiny261a</samp> defines +<code>__AVR_ATtiny261A__</code>, etc. +</p> +<p>The built-in macros’ names follow +the scheme <code>__AVR_<var>Device</var>__</code> where <var>Device</var> is +the device name as from the AVR user manual. The difference between +<var>Device</var> in the built-in macro and <var>device</var> in +<samp>-mmcu=<var>device</var></samp> is that the latter is always lowercase. +</p> +<p>If <var>device</var> is not a device but only a core architecture like +‘<samp>avr51</samp>’, this macro is not defined. +</p> +</dd> +<dt><code>__AVR_DEVICE_NAME__</code></dt> +<dd><p>Setting <samp>-mmcu=<var>device</var></samp> defines this built-in macro to +the device’s name. For example, with <samp>-mmcu=atmega8</samp> the macro +is defined to <code>atmega8</code>. +</p> +<p>If <var>device</var> is not a device but only a core architecture like +‘<samp>avr51</samp>’, this macro is not defined. +</p> +</dd> +<dt><code>__AVR_XMEGA__</code></dt> +<dd><p>The device / architecture belongs to the XMEGA family of devices. +</p> +</dd> +<dt><code>__AVR_HAVE_ELPM__</code></dt> +<dd><p>The device has the <code>ELPM</code> instruction. +</p> +</dd> +<dt><code>__AVR_HAVE_ELPMX__</code></dt> +<dd><p>The device has the <code>ELPM R<var>n</var>,Z</code> and <code>ELPM +R<var>n</var>,Z+</code> instructions. +</p> +</dd> +<dt><code>__AVR_HAVE_MOVW__</code></dt> +<dd><p>The device has the <code>MOVW</code> instruction to perform 16-bit +register-register moves. +</p> +</dd> +<dt><code>__AVR_HAVE_LPMX__</code></dt> +<dd><p>The device has the <code>LPM R<var>n</var>,Z</code> and +<code>LPM R<var>n</var>,Z+</code> instructions. +</p> +</dd> +<dt><code>__AVR_HAVE_MUL__</code></dt> +<dd><p>The device has a hardware multiplier. +</p> +</dd> +<dt><code>__AVR_HAVE_JMP_CALL__</code></dt> +<dd><p>The device has the <code>JMP</code> and <code>CALL</code> instructions. +This is the case for devices with more than 8 KiB of program +memory. +</p> +</dd> +<dt><code>__AVR_HAVE_EIJMP_EICALL__</code></dt> +<dt><code>__AVR_3_BYTE_PC__</code></dt> +<dd><p>The device has the <code>EIJMP</code> and <code>EICALL</code> instructions. +This is the case for devices with more than 128 KiB of program memory. +This also means that the program counter +(PC) is 3 bytes wide. +</p> +</dd> +<dt><code>__AVR_2_BYTE_PC__</code></dt> +<dd><p>The program counter (PC) is 2 bytes wide. This is the case for devices +with up to 128 KiB of program memory. +</p> +</dd> +<dt><code>__AVR_HAVE_8BIT_SP__</code></dt> +<dt><code>__AVR_HAVE_16BIT_SP__</code></dt> +<dd><p>The stack pointer (SP) register is treated as 8-bit respectively +16-bit register by the compiler. +The definition of these macros is affected by <samp>-mtiny-stack</samp>. +</p> +</dd> +<dt><code>__AVR_HAVE_SPH__</code></dt> +<dt><code>__AVR_SP8__</code></dt> +<dd><p>The device has the SPH (high part of stack pointer) special function +register or has an 8-bit stack pointer, respectively. +The definition of these macros is affected by <samp>-mmcu=</samp> and +in the cases of <samp>-mmcu=avr2</samp> and <samp>-mmcu=avr25</samp> also +by <samp>-msp8</samp>. +</p> +</dd> +<dt><code>__AVR_HAVE_RAMPD__</code></dt> +<dt><code>__AVR_HAVE_RAMPX__</code></dt> +<dt><code>__AVR_HAVE_RAMPY__</code></dt> +<dt><code>__AVR_HAVE_RAMPZ__</code></dt> +<dd><p>The device has the <code>RAMPD</code>, <code>RAMPX</code>, <code>RAMPY</code>, +<code>RAMPZ</code> special function register, respectively. +</p> +</dd> +<dt><code>__NO_INTERRUPTS__</code></dt> +<dd><p>This macro reflects the <samp>-mno-interrupts</samp> command-line option. +</p> +</dd> +<dt><code>__AVR_ERRATA_SKIP__</code></dt> +<dt><code>__AVR_ERRATA_SKIP_JMP_CALL__</code></dt> +<dd><p>Some AVR devices (AT90S8515, ATmega103) must not skip 32-bit +instructions because of a hardware erratum. Skip instructions are +<code>SBRS</code>, <code>SBRC</code>, <code>SBIS</code>, <code>SBIC</code> and <code>CPSE</code>. +The second macro is only defined if <code>__AVR_HAVE_JMP_CALL__</code> is also +set. +</p> +</dd> +<dt><code>__AVR_ISA_RMW__</code></dt> +<dd><p>The device has Read-Modify-Write instructions (XCH, LAC, LAS and LAT). +</p> +</dd> +<dt><code>__AVR_SFR_OFFSET__=<var>offset</var></code></dt> +<dd><p>Instructions that can address I/O special function registers directly +like <code>IN</code>, <code>OUT</code>, <code>SBI</code>, etc. may use a different +address as if addressed by an instruction to access RAM like <code>LD</code> +or <code>STS</code>. This offset depends on the device architecture and has +to be subtracted from the RAM address in order to get the +respective I/O address. +</p> +</dd> +<dt><code>__AVR_SHORT_CALLS__</code></dt> +<dd><p>The <samp>-mshort-calls</samp> command line option is set. +</p> +</dd> +<dt><code>__AVR_PM_BASE_ADDRESS__=<var>addr</var></code></dt> +<dd><p>Some devices support reading from flash memory by means of <code>LD*</code> +instructions. The flash memory is seen in the data address space +at an offset of <code>__AVR_PM_BASE_ADDRESS__</code>. If this macro +is not defined, this feature is not available. If defined, +the address space is linear and there is no need to put +<code>.rodata</code> into RAM. This is handled by the default linker +description file, and is currently available for +<code>avrtiny</code> and <code>avrxmega3</code>. Even more convenient, +there is no need to use address spaces like <code>__flash</code> or +features like attribute <code>progmem</code> and <code>pgm_read_*</code>. +</p> +</dd> +<dt><code>__WITH_AVRLIBC__</code></dt> +<dd><p>The compiler is configured to be used together with AVR-Libc. +See the <samp>--with-avrlibc</samp> configure option. +</p> +</dd> +<dt><code>__HAVE_DOUBLE_MULTILIB__</code></dt> +<dd><p>Defined if <samp>-mdouble=</samp> acts as a multilib option. +</p> +</dd> +<dt><code>__HAVE_DOUBLE32__</code></dt> +<dt><code>__HAVE_DOUBLE64__</code></dt> +<dd><p>Defined if the compiler supports 32-bit double resp. 64-bit double. +The actual layout is specified by option <samp>-mdouble=</samp>. +</p> +</dd> +<dt><code>__DEFAULT_DOUBLE__</code></dt> +<dd><p>The size in bits of <code>double</code> if <samp>-mdouble=</samp> is not set. +To test the layout of <code>double</code> in a program, use the built-in +macro <code>__SIZEOF_DOUBLE__</code>. +</p> +</dd> +<dt><code>__HAVE_LONG_DOUBLE32__</code></dt> +<dt><code>__HAVE_LONG_DOUBLE64__</code></dt> +<dt><code>__HAVE_LONG_DOUBLE_MULTILIB__</code></dt> +<dt><code>__DEFAULT_LONG_DOUBLE__</code></dt> +<dd><p>Same as above, but for <code>long double</code> instead of <code>double</code>. +</p> +</dd> +<dt><code>__WITH_DOUBLE_COMPARISON__</code></dt> +<dd><p>Reflects the <code>--with-double-comparison={tristate|bool|libf7}</code> +<a href="https://gcc.gnu.org/install/configure.html#avr">configure option</a><!-- /@w --> +and is defined to <code>2</code> or <code>3</code>. +</p> +</dd> +<dt><code>__WITH_LIBF7_LIBGCC__</code></dt> +<dt><code>__WITH_LIBF7_MATH__</code></dt> +<dt><code>__WITH_LIBF7_MATH_SYMBOLS__</code></dt> +<dd><p>Reflects the <code>--with-libf7={libgcc|math|math-symbols}</code> +<a href="https://gcc.gnu.org/install/configure.html#avr">configure option</a><!-- /@w -->. +</p> +</dd> +</dl> + +<hr> +<div class="header"> +<p> +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="previous">ARM Options</a>, Up: <a href="Submodel-Options.html#Submodel-Options" accesskey="u" rel="up">Submodel Options</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Indices.html#Indices" title="Index" rel="index">Index</a>]</p> +</div> + + + +</body> +</html> |