#ifndef ARM_SEMIHOSTING_H_
#define ARM_SEMIHOSTING_H_

// ----------------------------------------------------------------------------

// Semihosting operations.
enum OperationNumber
{
    // Regular operations
    SEMIHOSTING_EnterSVC = 0x17,
    SEMIHOSTING_ReportException = 0x18,
    SEMIHOSTING_SYS_CLOSE = 0x02,
    SEMIHOSTING_SYS_CLOCK = 0x10,
    SEMIHOSTING_SYS_ELAPSED = 0x30,
    SEMIHOSTING_SYS_ERRNO = 0x13,
    SEMIHOSTING_SYS_FLEN = 0x0C,
    SEMIHOSTING_SYS_GET_CMDLINE = 0x15,
    SEMIHOSTING_SYS_HEAPINFO = 0x16,
    SEMIHOSTING_SYS_ISERROR = 0x08,
    SEMIHOSTING_SYS_ISTTY = 0x09,
    SEMIHOSTING_SYS_OPEN = 0x01,
    SEMIHOSTING_SYS_READ = 0x06,
    SEMIHOSTING_SYS_READC = 0x07,
    SEMIHOSTING_SYS_REMOVE = 0x0E,
    SEMIHOSTING_SYS_RENAME = 0x0F,
    SEMIHOSTING_SYS_SEEK = 0x0A,
    SEMIHOSTING_SYS_SYSTEM = 0x12,
    SEMIHOSTING_SYS_TICKFREQ = 0x31,
    SEMIHOSTING_SYS_TIME = 0x11,
    SEMIHOSTING_SYS_TMPNAM = 0x0D,
    SEMIHOSTING_SYS_WRITE = 0x05,
    SEMIHOSTING_SYS_WRITEC = 0x03,
    SEMIHOSTING_SYS_WRITE0 = 0x04,

    // Codes returned by SEMIHOSTING_ReportException
    ADP_Stopped_ApplicationExit = ((2 << 16) + 38),
    ADP_Stopped_RunTimeError = ((2 << 16) + 35),

};

// ----------------------------------------------------------------------------

// SWI numbers and reason codes for RDI (Angel) monitors.
#define AngelSWI_ARM                    0x123456
#ifdef __thumb__
#define AngelSWI                        0xAB
#else
#define AngelSWI                        AngelSWI_ARM
#endif
// For thumb only architectures use the BKPT instruction instead of SWI.
#if defined(__ARM_ARCH_7M__)     \
    || defined(__ARM_ARCH_7EM__) \
    || defined(__ARM_ARCH_6M__)
#define AngelSWIInsn                    "bkpt"
#define AngelSWIAsm                     bkpt
#else
#define AngelSWIInsn                    "swi"
#define AngelSWIAsm                     swi
#endif

#if defined(OS_DEBUG_SEMIHOSTING_FAULTS)
// Testing the local semihosting handler cannot use another BKPT, since this
// configuration cannot trigger HaedFault exceptions while the debugger is
// connected, so we use an illegal op code, that will trigger an
// UsageFault exception.
#define AngelSWITestFault       "setend be"
#define AngelSWITestFaultOpCode (0xB658)
#endif

static inline int
__attribute__ ((always_inline))
call_host (int reason, void* arg)
{
    int value;
    asm volatile (

        " mov r0, %[rsn]  \n"
        " mov r1, %[arg]  \n"
#if defined(OS_DEBUG_SEMIHOSTING_FAULTS)
        " " AngelSWITestFault " \n"
#else
        " " AngelSWIInsn " %[swi] \n"
#endif
        " mov %[val], r0"

        : [val] "=r" (value) /* Outputs */
        : [rsn] "r" (reason), [arg] "r" (arg), [swi] "i" (AngelSWI) /* Inputs */
        : "r0", "r1", "r2", "r3", "ip", "lr", "memory", "cc"
        // Clobbers r0 and r1, and lr if in supervisor mode
    );

    // Accordingly to page 13-77 of ARM DUI 0040D other registers
    // can also be clobbered. Some memory positions may also be
    // changed by a system call, so they should not be kept in
    // registers. Note: we are assuming the manual is right and
    // Angel is respecting the APCS.
    return value;
}

// ----------------------------------------------------------------------------

// Function used in _exit() to return the status code as Angel exception.
static inline void
__attribute__ ((always_inline,noreturn))
report_exception (int reason)
{
    call_host (SEMIHOSTING_ReportException, (void*) reason);

    for (;;)
        ;
}

// ----------------------------------------------------------------------------

#endif // ARM_SEMIHOSTING_H_