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76 lines
2.2 KiB
C
76 lines
2.2 KiB
C
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/*
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* SPDX-FileCopyrightText: 2017, Intel Corporation
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*
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* SPDX-License-Identifier: Apache-2.0
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*
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* SPDX-FileContributor: 2016-2022 Espressif Systems (Shanghai) CO LTD
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*/
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/* File adapted to use on IDF FreeRTOS component, extracted
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* originally from zephyr RTOS code base:
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* https://github.com/zephyrproject-rtos/zephyr/blob/dafd348/arch/xtensa/include/xtensa-asm2-s.h
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*/
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#ifndef __XT_ASM_UTILS_H
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#define __XT_ASM_UTILS_H
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/*
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* SPILL_ALL_WINDOWS
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*
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* Spills all windowed registers (i.e. registers not visible as
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* A0-A15) to their ABI-defined spill regions on the stack.
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*
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* Unlike the Xtensa HAL implementation, this code requires that the
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* EXCM and WOE bit be enabled in PS, and relies on repeated hardware
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* exception handling to do the register spills. The trick is to do a
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* noop write to the high registers, which the hardware will trap
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* (into an overflow exception) in the case where those registers are
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* already used by an existing call frame. Then it rotates the window
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* and repeats until all but the A0-A3 registers of the original frame
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* are guaranteed to be spilled, eventually rotating back around into
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* the original frame. Advantages:
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*
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* - Vastly smaller code size
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*
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* - More easily maintained if changes are needed to window over/underflow
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* exception handling.
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*
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* - Requires no scratch registers to do its work, so can be used safely in any
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* context.
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*
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* - If the WOE bit is not enabled (for example, in code written for
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* the CALL0 ABI), this becomes a silent noop and operates compatbily.
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*
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* - Hilariously it's ACTUALLY FASTER than the HAL routine. And not
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* just a little bit, it's MUCH faster. With a mostly full register
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* file on an LX6 core (ESP-32) I'm measuring 145 cycles to spill
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* registers with this vs. 279 (!) to do it with
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* xthal_spill_windows().
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*/
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.macro SPILL_ALL_WINDOWS
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#if XCHAL_NUM_AREGS == 64
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and a12, a12, a12
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rotw 3
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and a12, a12, a12
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rotw 3
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and a12, a12, a12
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rotw 3
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and a12, a12, a12
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rotw 3
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and a12, a12, a12
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rotw 4
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#elif XCHAL_NUM_AREGS == 32
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and a12, a12, a12
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rotw 3
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and a12, a12, a12
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rotw 3
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and a4, a4, a4
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rotw 2
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#else
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#error Unrecognized XCHAL_NUM_AREGS
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#endif
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.endm
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#endif
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