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| <a name="RX-Options-1"></a> |
| <h4 class="subsection">3.17.38 RX Options</h4> |
| <a name="index-RX-Options"></a> |
| |
| <p>These command-line options are defined for RX targets: |
| </p> |
| <dl compact="compact"> |
| <dt><code>-m64bit-doubles</code></dt> |
| <dt><code>-m32bit-doubles</code></dt> |
| <dd><a name="index-m64bit_002ddoubles-1"></a> |
| <a name="index-m32bit_002ddoubles-1"></a> |
| <p>Make the <code>double</code> data type be 64 bits (<samp>-m64bit-doubles</samp>) |
| or 32 bits (<samp>-m32bit-doubles</samp>) in size. The default is |
| <samp>-m32bit-doubles</samp>. <em>Note</em> RX floating-point hardware only |
| works on 32-bit values, which is why the default is |
| <samp>-m32bit-doubles</samp>. |
| </p> |
| </dd> |
| <dt><code>-fpu</code></dt> |
| <dt><code>-nofpu</code></dt> |
| <dd><a name="index-fpu"></a> |
| <a name="index-nofpu"></a> |
| <p>Enables (<samp>-fpu</samp>) or disables (<samp>-nofpu</samp>) the use of RX |
| floating-point hardware. The default is enabled for the RX600 |
| series and disabled for the RX200 series. |
| </p> |
| <p>Floating-point instructions are only generated for 32-bit floating-point |
| values, however, so the FPU hardware is not used for doubles if the |
| <samp>-m64bit-doubles</samp> option is used. |
| </p> |
| <p><em>Note</em> If the <samp>-fpu</samp> option is enabled then |
| <samp>-funsafe-math-optimizations</samp> is also enabled automatically. |
| This is because the RX FPU instructions are themselves unsafe. |
| </p> |
| </dd> |
| <dt><code>-mcpu=<var>name</var></code></dt> |
| <dd><a name="index-mcpu-9"></a> |
| <p>Selects the type of RX CPU to be targeted. Currently three types are |
| supported, the generic ‘<samp>RX600</samp>’ and ‘<samp>RX200</samp>’ series hardware and |
| the specific ‘<samp>RX610</samp>’ CPU. The default is ‘<samp>RX600</samp>’. |
| </p> |
| <p>The only difference between ‘<samp>RX600</samp>’ and ‘<samp>RX610</samp>’ is that the |
| ‘<samp>RX610</samp>’ does not support the <code>MVTIPL</code> instruction. |
| </p> |
| <p>The ‘<samp>RX200</samp>’ series does not have a hardware floating-point unit |
| and so <samp>-nofpu</samp> is enabled by default when this type is |
| selected. |
| </p> |
| </dd> |
| <dt><code>-mbig-endian-data</code></dt> |
| <dt><code>-mlittle-endian-data</code></dt> |
| <dd><a name="index-mbig_002dendian_002ddata"></a> |
| <a name="index-mlittle_002dendian_002ddata"></a> |
| <p>Store data (but not code) in the big-endian format. The default is |
| <samp>-mlittle-endian-data</samp>, i.e. to store data in the little-endian |
| format. |
| </p> |
| </dd> |
| <dt><code>-msmall-data-limit=<var>N</var></code></dt> |
| <dd><a name="index-msmall_002ddata_002dlimit"></a> |
| <p>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 (usually <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 are pushed onto |
| the stack instead of being held in this register. |
| </p> |
| <p>Note, common variables (variables that have not been initialized) and |
| constants are not placed into the small data area as they are assigned |
| to other sections in the output executable. |
| </p> |
| <p>The default value is zero, which disables this feature. Note, this |
| feature is not enabled by default with higher optimization levels |
| (<samp>-O2</samp> etc) because of the potentially detrimental effects of |
| reserving a register. It is up to the programmer to experiment and |
| discover whether this feature is of benefit to their program. See the |
| description of the <samp>-mpid</samp> option for a description of how the |
| actual register to hold the small data area pointer is chosen. |
| </p> |
| </dd> |
| <dt><code>-msim</code></dt> |
| <dt><code>-mno-sim</code></dt> |
| <dd><a name="index-msim-8"></a> |
| <a name="index-mno_002dsim"></a> |
| <p>Use the simulator runtime. The default is to use the libgloss |
| board-specific runtime. |
| </p> |
| </dd> |
| <dt><code>-mas100-syntax</code></dt> |
| <dt><code>-mno-as100-syntax</code></dt> |
| <dd><a name="index-mas100_002dsyntax"></a> |
| <a name="index-mno_002das100_002dsyntax"></a> |
| <p>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 it is not generated by default. |
| </p> |
| </dd> |
| <dt><code>-mmax-constant-size=<var>N</var></code></dt> |
| <dd><a name="index-mmax_002dconstant_002dsize"></a> |
| <p>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> |
| <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. |
| </p> |
| </dd> |
| <dt><code>-mrelax</code></dt> |
| <dd><a name="index-mrelax-5"></a> |
| <p>Enable linker relaxation. Linker relaxation is a process whereby the |
| linker attempts to reduce the size of a program by finding shorter |
| versions of various instructions. Disabled by default. |
| </p> |
| </dd> |
| <dt><code>-mint-register=<var>N</var></code></dt> |
| <dd><a name="index-mint_002dregister"></a> |
| <p>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> is 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. |
| </p> |
| </dd> |
| <dt><code>-msave-acc-in-interrupts</code></dt> |
| <dd><a name="index-msave_002dacc_002din_002dinterrupts"></a> |
| <p>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. |
| </p> |
| </dd> |
| <dt><code>-mpid</code></dt> |
| <dt><code>-mno-pid</code></dt> |
| <dd><a name="index-mpid"></a> |
| <a name="index-mno_002dpid"></a> |
| <p>Enables the generation of position independent data. When enabled any |
| access to constant data is done via an offset from a base address |
| held in a register. This allows the location of constant data to be |
| determined at run time without requiring the executable to be |
| relocated, which is a benefit to embedded applications with tight |
| memory constraints. Data that can be modified is not affected by this |
| option. |
| </p> |
| <p>Note, using this feature reserves a register, usually <code>r13</code>, for |
| the constant data base address. This can result in slower and/or |
| larger code, especially in complicated functions. |
| </p> |
| <p>The actual register chosen to hold the constant data base address |
| depends upon whether the <samp>-msmall-data-limit</samp> and/or the |
| <samp>-mint-register</samp> command-line options are enabled. Starting |
| with register <code>r13</code> and proceeding downwards, registers are |
| allocated first to satisfy the requirements of <samp>-mint-register</samp>, |
| then <samp>-mpid</samp> and finally <samp>-msmall-data-limit</samp>. Thus it |
| is possible for the small data area register to be <code>r8</code> if both |
| <samp>-mint-register=4</samp> and <samp>-mpid</samp> are specified on the |
| command line. |
| </p> |
| <p>By default this feature is not enabled. The default can be restored |
| via the <samp>-mno-pid</samp> command-line option. |
| </p> |
| </dd> |
| <dt><code>-mno-warn-multiple-fast-interrupts</code></dt> |
| <dt><code>-mwarn-multiple-fast-interrupts</code></dt> |
| <dd><a name="index-mno_002dwarn_002dmultiple_002dfast_002dinterrupts"></a> |
| <a name="index-mwarn_002dmultiple_002dfast_002dinterrupts"></a> |
| <p>Prevents GCC from issuing a warning message if it finds more than one |
| fast interrupt handler when it is compiling a file. The default is to |
| issue a warning for each extra fast interrupt handler found, as the RX |
| only supports one such interrupt. |
| </p> |
| </dd> |
| </dl> |
| |
| <p><em>Note:</em> The generic GCC command-line option <samp>-ffixed-<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 ensures |
| 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>-ffixed-<var>reg</var></samp> or <samp>-mint-register</samp> command-line |
| options. |
| </p> |
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