71 lines
2.3 KiB
ArmAsm
71 lines
2.3 KiB
ArmAsm
/***************************************************************************
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* Copyright (C) 2014 Angus Gratton *
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* gus@projectgus.com *
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* *
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* This program is free software; you can redistribute it and/or modify *
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* it under the terms of the GNU General Public License as published by *
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* the Free Software Foundation; either version 2 of the License, or *
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* (at your option) any later version. *
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* *
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* This program is distributed in the hope that it will be useful, *
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* but WITHOUT ANY WARRANTY; without even the implied warranty of *
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the *
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* GNU General Public License for more details. *
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* *
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* You should have received a copy of the GNU General Public License *
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* along with this program; if not, write to the *
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* Free Software Foundation, Inc. *
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***************************************************************************/
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.text
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.syntax unified
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.cpu cortex-m0
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.thumb
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/*
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* Params :
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* r0 = byte count
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* r1 = buffer start
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* r2 = buffer end
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* r3 = target address
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* r6 = watchdog refresh value
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* r7 = watchdog refresh register address
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*/
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.thumb_func
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.global _start
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_start:
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wait_fifo:
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// Kick the watchdog
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str r6, [r7, #0]
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// Load write pointer
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ldr r5, [r1, #0]
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// Abort if it is NULL
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cmp r5, #0
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beq.n exit
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// Load read pointer
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ldr r4, [r1, #4]
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// Continue waiting if it equals the write pointer
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cmp r4, r5
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beq.n wait_fifo
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// Copy one word from buffer to target, and increment pointers
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ldmia r4!, {r5}
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stmia r3!, {r5}
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// If at end of buffer, wrap back to buffer start
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cmp r4, r2
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bcc.n no_wrap
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mov r4, r1
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adds r4, #8
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no_wrap:
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// Update read pointer inside the buffer
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str r4, [r1, #4]
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// Deduce the word transferred from the byte count
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subs r0, #4
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// Start again
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bne.n wait_fifo
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exit:
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// Wait for OpenOCD
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bkpt #0x00
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.pool
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