/****************************************************************************
 * arch/z80/src/z8/switch.h
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ****************************************************************************/

#ifndef __ARCH_Z80_SRC_Z8_SWITCH_H
#define __ARCH_Z80_SRC_Z8_SWITCH_H

/****************************************************************************
 * Included Files
 ****************************************************************************/

#ifndef __ASSEMBLY__
#  include <stdint.h>
#  include <nuttx/sched.h>
#  include <nuttx/arch.h>
#endif
#include "z80_internal.h"

/****************************************************************************
 * Pre-processor Definitions
 ****************************************************************************/

/* Z8_IRQSTATE_* definitions ************************************************
 * These are used in the state field of 'struct z8_irqstate_s' structure
 * to define the current state of the interrupt handling.
 * These definition support "lazy" interrupt context saving. See comments
 * below associated with s'truct z8_irqstate_s'.
 */

#define Z8_IRQSTATE_NONE  0 /* Not handling an interrupt */
#define Z8_IRQSTATE_ENTRY 1 /* In interrupt, context has not been saved */
#define Z8_IRQSTATE_SAVED 2 /* In interrupt, context has been saved */

/* The information saved on interrupt entry can be retained in a array of two
 * uint24_t values.  These are
 *
 *   value[0] = RP (MS byte) and Flags (LS) byte
 *   value[1] = PC
 *
 * The pointer to the save structure is a stack pointer at the time
 * that z80_doirq() was called:
 *
 *         PC[7:0]
 *         PC[15:8]
 *         Flags Register
 *   SP -> RP
 *
 * The stack pointer on return from interrupt can be obtained by adding 4
 * to the pointer to the save structure.
 */

#define Z8_IRQSAVE_RPFLAGS    (0)                      /* Index 10: RP (MS) and FLAGS (LS) */
#define Z8_IRQSAVE_PC         (1)                      /* Index 2: PC[8:15] */
#define Z8_IRQSAVE_REGS       (2)                      /* Number 16-bit values saved */

/* Byte offsets */

#define Z8_IRQSAVE_RP_OFFS    (2*Z8_IRQSAVE_RPFLAGS)   /* Offset 0: RP */
#define Z8_IRQSAVE_FLAGS_OFFS (2*Z8_IRQSAVE_RPFLAGS+1) /* Offset 1: FLAGS */
#define Z8_IRQSAVE_PCH_OFFS   (2*Z8_IRQSAVE_PC)        /* Offset 2: PC[8:15] */
#define Z8_IRQSAVE_PCL_OFFS   (2*Z8_IRQSAVE_PC+1)      /* Offset 3: PC[0:7] */
#define Z8_IRQSAVE_SIZE       (2*Z8_IRQSAVE_REGS)      /* Number 8-bit values saved */

/* Macros for portability ***************************************************
 *
 * Common logic in arch/z80/src/common is customized for the z8
 * context switching logic via the following macros.
 */

/* Initialize the IRQ state */

#define INIT_IRQCONTEXT() \
  do { \
    g_z8irqstate.state = Z8_IRQSTATE_NONE; \
  } while (0)

/* IN_INTERRUPT returns true if the system is currently operating in the
 * interrupt context.  IN_INTERRUPT is the inline equivalent
 * of up_interrupt_context().
 */

#define IN_INTERRUPT() \
  (g_z8irqstate.state != Z8_IRQSTATE_NONE)

/* The following macro is used when the system enters interrupt
 * handling logic
 *
 * NOTE: Nested interrupts are not supported in this implementation.  If you
 * want to implement nested interrupts, you would have to change the way that
 * g_current_regs is handled.  The savestate variable would not work for
 * that purpose as implemented here because only the outermost nested
 * interrupt can result in a context switch (it can probably be deleted).
 */

#define DECL_SAVESTATE() \
  struct z8_irqstate_s savestate

#define IRQ_ENTER(irq, regs) \
  do { \
    savestate.state    = g_z8irqstate.state; \
    savestate.regs     = g_z8irqstate.regs; \
    g_z8irqstate.state = Z8_IRQSTATE_ENTRY; \
    g_z8irqstate.regs  = (regs); \
    up_ack_irq(irq); \
  } while (0)

/* The following macro is used when the system exits interrupt
 * handling logic
 */

#define IRQ_LEAVE(irq) \
  do { \
    g_z8irqstate.state = savestate.state; \
    g_z8irqstate.regs  = savestate.regs; \
  } while (0)

/* The following macro is used to sample the interrupt state
 * (as a opaque handle)
 */

#define IRQ_STATE() \
  (g_z8irqstate.regs)

/* Save the current IRQ context in the specified TCB */

#define SAVE_IRQCONTEXT(tcb) \
  z8_saveirqcontext((tcb)->xcp.regs)

/* Set the current IRQ context to the state specified in the TCB */

#define SET_IRQCONTEXT(tcb) \
  do { \
    g_z8irqstate.state = Z8_IRQSTATE_SAVED; \
    g_z8irqstate.regs  = (tcb)->xcp.regs; \
  } while (0)

/* Save the user context in the specified TCB.  User context saves
 * can be simpler because only those registers normally
 * saved in a C called need be stored.
 */

#define SAVE_USERCONTEXT(tcb) \
  up_saveusercontext((tcb)->xcp.regs)

/* Restore the full context -- either a simple user state save or the full,
 * IRQ state save.
 */

#define RESTORE_USERCONTEXT(tcb) \
  z8_restorecontext((tcb)->xcp.regs)

/****************************************************************************
 * Public Types
 ****************************************************************************/

/* In order to provide faster interrupt handling, the interrupt logic does
 * "lazy" context saving as described below:
 *
 * (1) At the time of the interrupt, minimum information is saved and the
 *     register pointer is changed so that the interrupt logic does not alter
 *     the state of the interrupted task's registers.
 * (2) If no context switch occurs during the interrupt processing, then
 *     the return from interrupt is also simple.
 * (3) If a context switch occurs during interrupt processing, then
 *     (a) The full context of the interrupt task is saved, and
 *     (b) A full context switch is performed when the interrupt exits (see
 *         z8_vector.S).
 *
 * The following structure is used to manage this "lazy" context saving.
 */

#ifndef __ASSEMBLY__
struct z8_irqstate_s
{
  uint8_t    state; /* See Z8_IRQSTATE_* definitions above */
  chipreg_t *regs;  /* Saved register information */
};
#endif

/****************************************************************************
 * Public Data
 ****************************************************************************/

#ifndef __ASSEMBLY__
/* This structure holds information about the current interrupt
 * processing state
 */

extern struct z8_irqstate_s g_z8irqstate;
#endif

/****************************************************************************
 * Public Function Prototypes
 ****************************************************************************/

#ifndef __ASSEMBLY__
#ifdef __cplusplus
extern "C"
{
#endif

/* Defined in z8_irq.c */

void up_ack_irq(int irq);

/* Defined in z8_saveusercontext.asm */

int up_saveusercontext(FAR chipreg_t *regs);

/* Defined in z8_saveirqcontext.c */

void z8_saveirqcontext(FAR chipreg_t *regs);

/* Defined in z8_restorecontext.asm */

void z8_restorecontext(FAR chipreg_t *regs);

/* Defined in z8_sigsetup.c */

void z8_sigsetup(FAR struct tcb_s *tcb, sig_deliver_t sigdeliver,
                 FAR chipreg_t *regs);

#ifdef __cplusplus
}
#endif
#endif

#endif /* __ARCH_Z80_SRC_Z8_SWITCH_H */