9e21dbf5c8
git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@1640 42af7a65-404d-4744-a932-0658087f49c3
111 lines
4.2 KiB
NASM
111 lines
4.2 KiB
NASM
;**************************************************************************
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; arch/z80/src/ez80/ez80_restorcontext.asm
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;
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; Copyright (C) 2008-2009 Gregory Nutt. All rights reserved.
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; Author: Gregory Nutt <spudmonkey@racsa.co.cr>
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;
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; Redistribution and use in source and binary forms, with or without
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; modification, are permitted provided that the following conditions
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; are met:
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;
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; 1. Redistributions of source code must retain the above copyright
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; notice, this list of conditions and the following disclaimer.
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; 2. Redistributions in binary form must reproduce the above copyright
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; notice, this list of conditions and the following disclaimer in
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; the documentation and/or other materials provided with the
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; distribution.
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; 3. Neither the name NuttX nor the names of its contributors may be
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; used to endorse or promote products derived from this software
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; without specific prior written permission.
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;
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; THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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; "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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; LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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; FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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; COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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; INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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; BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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; OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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; AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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; LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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; ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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; POSSIBILITY OF SUCH DAMAGE.
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;
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;**************************************************************************
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;**************************************************************************
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; Global Symbols Imported
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;**************************************************************************
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;**************************************************************************
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; Global Symbols Expported
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;**************************************************************************
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xdef _ez80_restorecontext
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;**************************************************************************
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; Code
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;**************************************************************************
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segment CODE
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.assume ADL=1
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;**************************************************************************
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; ez80_restorecontext
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;**************************************************************************
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_ez80_restorecontext:
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; On entry, stack contains return address (not used), then address
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; of the register save structure
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; Discard the return address, we won't be returning
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pop hl
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; Get the address of the beginning of the state save area. Each
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; pop will increment to the next element of the structure
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pop hl ; BC = Address of save structure
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ld sp, hl ; SP points to top of storage area
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; Disable interrupts while we muck with the alternative registers. The
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; Correct interrupt state will be restore below
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di
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; Restore registers. HL points to the beginning of the reg structure to restore
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ex af, af' ; Select alternate AF
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pop af ; Offset 0: AF' = I with interrupt state in parity
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ex af, af' ; Restore original AF
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pop bc ; Offset 1: BC
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pop de ; Offset 2: DE
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pop ix ; Offset 3: IX
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pop iy ; Offset 4: IY
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exx ; Use alternate BC/DE/HL
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pop hl ; Offset 5: HL' = Stack pointer after return
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exx ; Restore original BC/DE/HL
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pop hl ; Offset 6: HL
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pop af ; Offset 7: AF
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; Restore the stack pointer
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exx ; Use alternate BC/DE/HL
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pop de ; DE' = return address
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ld sp, hl ; Set SP = saved stack pointer value before return
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push de ; Save return address for ret instruction
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exx ; Restore original BC/DE/HL
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; Restore interrupt state
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ex af, af' ; Recover interrupt state
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jp po, noinrestore ; Odd parity, IFF2=0, means disabled
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ex af, af' ; Restore AF (before enabling interrupts)
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ei ; yes.. Enable interrupts
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ret ; and return
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noinrestore:
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ex af, af' ; Restore AF
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ret ; Return with interrupts disabled
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end
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