These options are defined for AVR implementations:
-mmcu=mcu
The default for this option is ‘avr2’.
GCC supports the following AVR devices and ISAs:
avr2attiny22, attiny26, at90c8534, at90s2313, at90s2323, at90s2333, at90s2343, at90s4414, at90s4433, at90s4434, at90s8515, at90s8535. avr25MOVW instruction. mcu = ata5272, ata6616c, attiny13, attiny13a, attiny2313, attiny2313a, attiny24, attiny24a, attiny25, attiny261, attiny261a, attiny43u, attiny4313, attiny44, attiny44a, attiny441, attiny45, attiny461, attiny461a, attiny48, attiny828, attiny84, attiny84a, attiny841, attiny85, attiny861, attiny861a, attiny87, attiny88, at86rf401. avr3at43usb355, at76c711. avr31atmega103, at43usb320. avr35MOVW instruction. mcu = ata5505, ata6617c, ata664251, atmega16u2, atmega32u2, atmega8u2, attiny1634, attiny167, at90usb162, at90usb82. avr4ata6285, ata6286, ata6289, ata6612c, atmega48, atmega48a, atmega48p, atmega48pa, atmega48pb, atmega8, atmega8a, atmega8hva, atmega8515, atmega8535, atmega88, atmega88a, atmega88p, atmega88pa, atmega88pb, at90pwm1, at90pwm2, at90pwm2b, at90pwm3, at90pwm3b, at90pwm81. avr5ata5702m322, ata5782, ata5790, ata5790n, ata5791, ata5795, ata5831, ata6613c, ata6614q, ata8210, ata8510, atmega16, atmega16a, atmega16hva, atmega16hva2, atmega16hvb, atmega16hvbrevb, atmega16m1, atmega16u4, atmega161, atmega162, atmega163, atmega164a, atmega164p, atmega164pa, atmega165, atmega165a, atmega165p, atmega165pa, atmega168, atmega168a, atmega168p, atmega168pa, atmega168pb, atmega169, atmega169a, atmega169p, atmega169pa, atmega32, atmega32a, atmega32c1, atmega32hvb, atmega32hvbrevb, atmega32m1, atmega32u4, atmega32u6, atmega323, atmega324a, atmega324p, atmega324pa, atmega325, atmega325a, atmega325p, atmega325pa, atmega3250, atmega3250a, atmega3250p, atmega3250pa, atmega328, atmega328p, atmega328pb, atmega329, atmega329a, atmega329p, atmega329pa, atmega3290, atmega3290a, atmega3290p, atmega3290pa, atmega406, atmega64, atmega64a, atmega64c1, atmega64hve, atmega64hve2, atmega64m1, atmega64rfr2, atmega640, atmega644, atmega644a, atmega644p, atmega644pa, atmega644rfr2, atmega645, atmega645a, atmega645p, atmega6450, atmega6450a, atmega6450p, atmega649, atmega649a, atmega649p, atmega6490, atmega6490a, atmega6490p, at90can32, at90can64, at90pwm161, at90pwm216, at90pwm316, at90scr100, at90usb646, at90usb647, at94k, m3000. avr51atmega128, atmega128a, atmega128rfa1, atmega128rfr2, atmega1280, atmega1281, atmega1284, atmega1284p, atmega1284rfr2, at90can128, at90usb1286, at90usb1287. avr6atmega256rfr2, atmega2560, atmega2561, atmega2564rfr2. avrxmega2atxmega16a4, atxmega16a4u, atxmega16c4, atxmega16d4, atxmega16e5, atxmega32a4, atxmega32a4u, atxmega32c3, atxmega32c4, atxmega32d3, atxmega32d4, atxmega32e5, atxmega8e5. avrxmega4atxmega64a3, atxmega64a3u, atxmega64a4u, atxmega64b1, atxmega64b3, atxmega64c3, atxmega64d3, atxmega64d4. avrxmega5atxmega64a1, atxmega64a1u. avrxmega6atxmega128a3, atxmega128a3u, atxmega128b1, atxmega128b3, atxmega128c3, atxmega128d3, atxmega128d4, atxmega192a3, atxmega192a3u, atxmega192c3, atxmega192d3, atxmega256a3, atxmega256a3b, atxmega256a3bu, atxmega256a3u, atxmega256c3, atxmega256d3, atxmega384c3, atxmega384d3. avrxmega7atxmega128a1, atxmega128a1u, atxmega128a4u. avrtinyattiny10, attiny20, attiny4, attiny40, attiny5, attiny9. avr1attiny11, attiny12, attiny15, attiny28, at90s1200. -maccumulate-argsPopping 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 to be removed from the stack after such a function call.
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.
-mbranch-cost=cost
-mcall-prologues-mint8int to be 8-bit integer. This affects the sizes of all types: a char is 1 byte, an int is 1 byte, a long is 2 bytes, and long long is 4 bytes. Please note that this option does not conform to the C standards, but it results in smaller code size. -mn-flash=num
-mno-interrupts-mrelaxCALL resp. JMP instruction by the shorter RCALL resp. RJMP instruction if applicable. Setting -mrelax just adds the --mlink-relax option to the assembler's command line and the --relax option to the linker's command line. 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.
Relaxing must be turned on if linker stubs are needed, see the section on EIND and linker stubs below.
-mrmwXCH, LAC, LAS and LAT. -msp8This option is used internally by the compiler to select and build multilibs for architectures avr2 and avr25. These architectures mix devices with and without SPH. For any setting other than -mmcu=avr2 or -mmcu=avr25 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 SPH register or not.
-mstrict-XX in a way proposed by the hardware. This means that X is only used in indirect, post-increment or pre-decrement addressing. Without this option, the X register may be used in the same way as Y or Z which then is emulated by additional instructions. For example, loading a value with X+const addressing with a small non-negative const < 64 to a register Rn is performed as
adiw r26, const ; X += const ld Rn, X ; Rn = *X sbiw r26, const ; X -= const
-mtiny-stack-nodeviceliblibdev.a. -Waddr-space-convertEIND and Devices with More Than 128 Ki Bytes of FlashPointers 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.
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 EIND that serves as most significant part of the target address when EICALL or EIJMP instructions are used.
Indirect jumps and calls on these devices are handled as follows by the compiler and are subject to some limitations:
EIND. EIND implicitly in EICALL/EIJMP instructions or might read EIND directly in order to emulate an indirect call/jump by means of a RET instruction. EIND never changes during the startup code or during the application. In particular, EIND is not saved/restored in function or interrupt service routine prologue/epilogue. -mrelax and the linker option --relax. There are corner cases where the linker is supposed to generate stubs but aborts without relaxation and without a helpful error message. EIND = 0. If code is supposed to work for a setup with EIND != 0, a custom linker script has to be used in order to place the sections whose name start with .trampolines into the segment where EIND points to. EIND. Notice that startup code is a blend of code from libgcc and AVR-LibC. For the impact of AVR-LibC on EIND, see the AVR-LibC user manual. EIND early, for example by means of initialization code located in section .init3. 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 EIND to the segment where the vector table is located. #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");
} The __trampolines_start symbol is defined in the linker script.
gs modifier (short for generate stubs) like so: LDI r24, lo8(gs(func)) LDI r25, hi8(gs(func))
gs modifiers for code labels in the following situations: -mcall-prologues command-line option. -fno-jump-tables command-line option. gs() modifier explained above. int main (void)
{
/* Call function at word address 0x2 */
return ((int(*)(void)) 0x2)();
} Instead, a stub has to be set up, i.e. the function has to be called through a symbol (func_4 in the example):
int main (void)
{
extern int func_4 (void);
/* Call function at byte address 0x4 */
return func_4();
} and the application be linked with -Wl,--defsym,func_4=0x4. Alternatively, func_4 can be defined in the linker script.
RAMPD, RAMPX, RAMPY and RAMPZ Special Function RegistersSome 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 contentent of a RAMP register is used as high part of the address: The X, Y, Z address register is concatenated with the RAMPX, RAMPY, RAMPZ special function register, respectively, to get a wide address. Similarly, RAMPD is used together with direct addressing.
RAMP special function registers with zero. __flash is used, then RAMPZ is set as needed before the operation. RAMPZ to accomplish an operation, RAMPZ is reset to zero after the operation. RAMP register, the ISR prologue/epilogue saves/restores that SFR and initializes it with zero in case the ISR code might (implicitly) use it. RAMP registers, you must reset it to zero after the access. 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 -mmcu= command-line option.
For even more AVR-specific built-in macros see AVR Named Address Spaces and AVR Built-in Functions.
__AVR_ARCH__2, 25, 3, 31, 35, 4, 5, 51, 6
for mcu=avr2, avr25, avr3, avr31, avr35, avr4, avr5, avr51, avr6,
respectively and
100, 102, 104, 105, 106, 107
for mcu=avrtiny, avrxmega2, avrxmega4, avrxmega5, avrxmega6, avrxmega7, respectively. If mcu specifies a device, this built-in macro is set accordingly. For example, with -mmcu=atmega8 the macro is defined to 4.
__AVR_Device__
-mmcu=atmega8 defines the built-in macro __AVR_ATmega8__, -mmcu=attiny261a defines __AVR_ATtiny261A__, etc. The built-in macros' names follow the scheme __AVR_Device__ where Device is the device name as from the AVR user manual. The difference between Device in the built-in macro and device in -mmcu=device is that the latter is always lowercase.
If device is not a device but only a core architecture like ‘avr51’, this macro is not defined.
__AVR_DEVICE_NAME__-mmcu=atmega8 the macro is defined to atmega8. If device is not a device but only a core architecture like ‘avr51’, this macro is not defined.
__AVR_XMEGA____AVR_HAVE_ELPM__ELPM instruction. __AVR_HAVE_ELPMX__ELPM Rn,Z and ELPM
Rn,Z+ instructions. __AVR_HAVE_MOVW__MOVW instruction to perform 16-bit register-register moves. __AVR_HAVE_LPMX__LPM Rn,Z and LPM Rn,Z+ instructions. __AVR_HAVE_MUL____AVR_HAVE_JMP_CALL__JMP and CALL instructions. This is the case for devices with at least 16 KiB of program memory. __AVR_HAVE_EIJMP_EICALL____AVR_3_BYTE_PC__EIJMP and EICALL 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. __AVR_2_BYTE_PC____AVR_HAVE_8BIT_SP____AVR_HAVE_16BIT_SP__-mtiny-stack. __AVR_HAVE_SPH____AVR_SP8__-mmcu= and in the cases of -mmcu=avr2 and -mmcu=avr25 also by -msp8. __AVR_HAVE_RAMPD____AVR_HAVE_RAMPX____AVR_HAVE_RAMPY____AVR_HAVE_RAMPZ__RAMPD, RAMPX, RAMPY, RAMPZ special function register, respectively. __NO_INTERRUPTS__-mno-interrupts command-line option. __AVR_ERRATA_SKIP____AVR_ERRATA_SKIP_JMP_CALL__SBRS, SBRC, SBIS, SBIC and CPSE. The second macro is only defined if __AVR_HAVE_JMP_CALL__ is also set. __AVR_ISA_RMW____AVR_SFR_OFFSET__=offset
IN, OUT, SBI, etc. may use a different address as if addressed by an instruction to access RAM like LD or STS. 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. __WITH_AVRLIBC__--with-avrlibc configure option.
© Free Software Foundation
Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-6.3.0/gcc/AVR-Options.html