frame.h

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#ifndef CPU_FRAME_H
#define CPU_FRAME_H

#include <cpu/detect.h>

#include "cfg/cfg_arch.h"      /* ARCH_EMUL */
#include <cfg/compiler.h>      /* for uintXX_t */

#if CPU_X86
    #if CPU_X86_32
        #define CPU_SAVED_REGS_CNT      2
    #elif CPU_X86_64
        #define CPU_SAVED_REGS_CNT      8
    #else
        #error "unknown CPU"
    #endif
    #define CPU_STACK_GROWS_UPWARD  0
    #define CPU_SP_ON_EMPTY_SLOT    0

#elif CPU_ARM

    #define CPU_SAVED_REGS_CNT     8
    #define CPU_STACK_GROWS_UPWARD 0
    #define CPU_SP_ON_EMPTY_SLOT   0

#elif CPU_PPC

    #define CPU_SAVED_REGS_CNT     1
    #define CPU_STACK_GROWS_UPWARD 0
    #define CPU_SP_ON_EMPTY_SLOT   1

#elif CPU_DSP56K

    #define CPU_SAVED_REGS_CNT      8
    #define CPU_STACK_GROWS_UPWARD  1
    #define CPU_SP_ON_EMPTY_SLOT    0

#elif CPU_AVR

    #define CPU_SAVED_REGS_CNT     18
    #define CPU_STACK_GROWS_UPWARD  0
    #define CPU_SP_ON_EMPTY_SLOT    1

#else
    #error No CPU_... defined.
#endif

#ifndef CPU_STACK_GROWS_UPWARD
    #error CPU_STACK_GROWS_UPWARD should have been defined to either 0 or 1
#endif

#ifndef CPU_SP_ON_EMPTY_SLOT
    #error CPU_SP_ON_EMPTY_SLOT should have been defined to either 0 or 1
#endif

#ifndef CPU_REG_INIT_VALUE
    #define CPU_REG_INIT_VALUE(reg)     (reg)
#endif

/*
 * Support stack handling peculiarities of a few CPUs.
 *
 * Most processors let their stack grow downward and
 * keep SP pointing at the last pushed value.
 */
#if !CPU_STACK_GROWS_UPWARD
    #if !CPU_SP_ON_EMPTY_SLOT
        /* Most microprocessors (x86, m68k...) */
        #define CPU_PUSH_WORD(sp, data) \
            do { *--(sp) = (data); } while (0)
        #define CPU_POP_WORD(sp) \
            (*(sp)++)
    #else
        /* AVR insanity */
        #define CPU_PUSH_WORD(sp, data) \
            do { *(sp)-- = (data); } while (0)
        #define CPU_POP_WORD(sp) \
            (*++(sp))
    #endif

#else /* CPU_STACK_GROWS_UPWARD */

    #if !CPU_SP_ON_EMPTY_SLOT
        /* DSP56K and other weirdos */
        #define CPU_PUSH_WORD(sp, data) \
            do { *++(sp) = (cpu_stack_t)(data); } while (0)
        #define CPU_POP_WORD(sp) \
            (*(sp)--)
    #else
        #error I bet you cannot find a CPU like this
    #endif
#endif


#if CPU_DSP56K
    /*
     * DSP56k pushes both PC and SR to the stack in the JSR instruction, but
     * RTS discards SR while returning (it does not restore it). So we push
     * 0 to fake the same context.
     */
    #define CPU_PUSH_CALL_FRAME(sp, func) \
        do { \
            CPU_PUSH_WORD((sp), (func)); \
            CPU_PUSH_WORD((sp), 0x100); \
        } while (0);

#elif CPU_AVR
    /*
     * On AVR, addresses are pushed into the stack as little-endian, while
     * memory accesses are big-endian (actually, it's a 8-bit CPU, so there is
     * no natural endianess).
     */
    #define CPU_PUSH_CALL_FRAME(sp, func) \
        do { \
            uint16_t funcaddr = (uint16_t)(func); \
            CPU_PUSH_WORD((sp), funcaddr); \
            CPU_PUSH_WORD((sp), funcaddr>>8); \
        } while (0)

    /*
     * If the kernel is in idle-spinning, the processor executes:
     *
     * IRQ_ENABLE;
     * CPU_IDLE;
     * IRQ_DISABLE;
     *
     * IRQ_ENABLE is translated in asm as "sei" and IRQ_DISABLE as "cli".
     * We could define CPU_IDLE to expand to none, so the resulting
     * asm code would be:
     *
     * sei;
     * cli;
     *
     * But Atmel datasheet states:
     * "When using the SEI instruction to enable interrupts,
     * the instruction following SEI will be executed *before*
     * any pending interrupts", so "cli" is executed before any
     * pending interrupt with the result that IRQs will *NOT*
     * be enabled!
     * To ensure that IRQ will run a NOP is required.
     */
    #define CPU_IDLE NOP

#elif CPU_PPC

    #define CPU_PUSH_CALL_FRAME(sp, func) \
        do { \
            CPU_PUSH_WORD((sp), (cpu_stack_t)(func)); /* LR -> 8(SP) */ \
            CPU_PUSH_WORD((sp), 0);                  /* CR -> 4(SP) */ \
        } while (0)

#else
    #define CPU_PUSH_CALL_FRAME(sp, func) \
        CPU_PUSH_WORD((sp), (cpu_stack_t)(func))
#endif

#ifndef CPU_IDLE
    #define CPU_IDLE PAUSE
#endif /* !CPU_IDLE */

#ifndef CPU_CREATE_NEW_STACK

    #define CPU_CREATE_NEW_STACK(stack) \
        do { \
            size_t i; \
            /* Initialize process stack frame */ \
            CPU_PUSH_CALL_FRAME(stack, proc_entry); \
            /* Push a clean set of CPU registers for asm_switch_context() */ \
            for (i = 0; i < CPU_SAVED_REGS_CNT; i++) \
                CPU_PUSH_WORD(stack, CPU_REG_INIT_VALUE(i)); \
        } while (0)
#endif

#endif /* CPU_ATTR_H */