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| <h4 class="subsection">3.17.32 RX Options</h4> |
| |
| <p><a name="index-RX-Options-1881"></a> |
| These command line options are defined for RX targets: |
| |
| <dl> |
| <dt><code>-m64bit-doubles</code><dt><code>-m32bit-doubles</code><dd><a name="index-m64bit_002ddoubles-1882"></a><a name="index-m32bit_002ddoubles-1883"></a>Make the <code>double</code> data type be 64-bits (<samp><span class="option">-m64bit-doubles</span></samp>) |
| or 32-bits (<samp><span class="option">-m32bit-doubles</span></samp>) in size. The default is |
| <samp><span class="option">-m32bit-doubles</span></samp>. <em>Note</em> RX floating point hardware only |
| works on 32-bit values, which is why the default is |
| <samp><span class="option">-m32bit-doubles</span></samp>. |
| |
| <br><dt><code>-fpu</code><dt><code>-nofpu</code><dd><a name="index-fpu-1884"></a><a name="index-nofpu-1885"></a>Enables (<samp><span class="option">-fpu</span></samp>) or disables (<samp><span class="option">-nofpu</span></samp>) the use of RX |
| floating point hardware. The default is enabled for the <var>RX600</var> |
| series and disabled for the <var>RX200</var> series. |
| |
| <p>Floating point instructions will only be generated for 32-bit floating |
| point values however, so if the <samp><span class="option">-m64bit-doubles</span></samp> option is in |
| use then the FPU hardware will not be used for doubles. |
| |
| <p><em>Note</em> If the <samp><span class="option">-fpu</span></samp> option is enabled then |
| <samp><span class="option">-funsafe-math-optimizations</span></samp> is also enabled automatically. |
| This is because the RX FPU instructions are themselves unsafe. |
| |
| <br><dt><code>-mcpu=</code><var>name</var><dt><code>-patch=</code><var>name</var><dd><a name="index-g_t_002dmcpu-1886"></a><a name="index-g_t_002dpatch-1887"></a>Selects the type of RX CPU to be targeted. Currently three types are |
| supported, the generic <var>RX600</var> and <var>RX200</var> series hardware and |
| the specific <var>RX610</var> cpu. The default is <var>RX600</var>. |
| |
| <p>The only difference between <var>RX600</var> and <var>RX610</var> is that the |
| <var>RX610</var> does not support the <code>MVTIPL</code> instruction. |
| |
| <p>The <var>RX200</var> series does not have a hardware floating point unit |
| and so <samp><span class="option">-nofpu</span></samp> is enabled by default when this type is |
| selected. |
| |
| <br><dt><code>-mbig-endian-data</code><dt><code>-mlittle-endian-data</code><dd><a name="index-mbig_002dendian_002ddata-1888"></a><a name="index-mlittle_002dendian_002ddata-1889"></a>Store data (but not code) in the big-endian format. The default is |
| <samp><span class="option">-mlittle-endian-data</span></samp>, ie to store data in the little endian |
| format. |
| |
| <br><dt><code>-msmall-data-limit=</code><var>N</var><dd><a name="index-msmall_002ddata_002dlimit-1890"></a>Specifies the maximum size in bytes of global and static variables |
| which can be placed into the small data area. Using the small data |
| area can lead to smaller and faster code, but the size of area is |
| limited and it is up to the programmer to ensure that the area does |
| not overflow. Also when the small data area is used one of the RX's |
| registers (<code>r13</code>) is reserved for use pointing to this area, so |
| it is no longer available for use by the compiler. This could result |
| in slower and/or larger code if variables which once could have been |
| held in <code>r13</code> are now pushed onto the stack. |
| |
| <p>Note, common variables (variables which have not been initialised) and |
| constants are not placed into the small data area as they are assigned |
| to other sections in the output executable. |
| |
| <p>The default value is zero, which disables this feature. Note, this |
| feature is not enabled by default with higher optimization levels |
| (<samp><span class="option">-O2</span></samp> etc) because of the potentially detrimental effects of |
| reserving register <code>r13</code>. It is up to the programmer to |
| experiment and discover whether this feature is of benefit to their |
| program. |
| |
| <br><dt><code>-msim</code><dt><code>-mno-sim</code><dd><a name="index-msim-1891"></a><a name="index-mno_002dsim-1892"></a>Use the simulator runtime. The default is to use the libgloss board |
| specific runtime. |
| |
| <br><dt><code>-mas100-syntax</code><dt><code>-mno-as100-syntax</code><dd><a name="index-mas100_002dsyntax-1893"></a><a name="index-mno_002das100_002dsyntax-1894"></a>When generating assembler output use a syntax that is compatible with |
| Renesas's AS100 assembler. This syntax can also be handled by the GAS |
| assembler but it has some restrictions so generating it is not the |
| default option. |
| |
| <br><dt><code>-mmax-constant-size=</code><var>N</var><dd><a name="index-mmax_002dconstant_002dsize-1895"></a>Specifies the maximum size, in bytes, of a constant that can be used as |
| an operand in a RX instruction. Although the RX instruction set does |
| allow constants of up to 4 bytes in length to be used in instructions, |
| a longer value equates to a longer instruction. Thus in some |
| circumstances it can be beneficial to restrict the size of constants |
| that are used in instructions. Constants that are too big are instead |
| placed into a constant pool and referenced via register indirection. |
| |
| <p>The value <var>N</var> can be between 0 and 4. A value of 0 (the default) |
| or 4 means that constants of any size are allowed. |
| |
| <br><dt><code>-mrelax</code><dd><a name="index-mrelax-1896"></a>Enable linker relaxation. Linker relaxation is a process whereby the |
| linker will attempt to reduce the size of a program by finding shorter |
| versions of various instructions. Disabled by default. |
| |
| <br><dt><code>-mint-register=</code><var>N</var><dd><a name="index-mint_002dregister-1897"></a>Specify the number of registers to reserve for fast interrupt handler |
| functions. The value <var>N</var> can be between 0 and 4. A value of 1 |
| means that register <code>r13</code> will be reserved for the exclusive use |
| of fast interrupt handlers. A value of 2 reserves <code>r13</code> and |
| <code>r12</code>. A value of 3 reserves <code>r13</code>, <code>r12</code> and |
| <code>r11</code>, and a value of 4 reserves <code>r13</code> through <code>r10</code>. |
| A value of 0, the default, does not reserve any registers. |
| |
| <br><dt><code>-msave-acc-in-interrupts</code><dd><a name="index-msave_002dacc_002din_002dinterrupts-1898"></a>Specifies that interrupt handler functions should preserve the |
| accumulator register. This is only necessary if normal code might use |
| the accumulator register, for example because it performs 64-bit |
| multiplications. The default is to ignore the accumulator as this |
| makes the interrupt handlers faster. |
| |
| </dl> |
| |
| <p><em>Note:</em> The generic GCC command line <samp><span class="option">-ffixed-</span><var>reg</var></samp> |
| has special significance to the RX port when used with the |
| <code>interrupt</code> function attribute. This attribute indicates a |
| function intended to process fast interrupts. GCC will will ensure |
| that it only uses the registers <code>r10</code>, <code>r11</code>, <code>r12</code> |
| and/or <code>r13</code> and only provided that the normal use of the |
| corresponding registers have been restricted via the |
| <samp><span class="option">-ffixed-</span><var>reg</var></samp> or <samp><span class="option">-mint-register</span></samp> command line |
| options. |
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