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[/] [neorv32/] [trunk/] [sw/] [ocd-firmware/] [park_loop.S] - Rev 63
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/* ################################################################################################# */
/* # << NEORV32 - park_loop.S - Execution-Based On-Chip Debugger - Park Loop Code >> # */
/* # ********************************************************************************************* # */
/* # BSD 3-Clause License # */
/* # # */
/* # Copyright (c) 2021, Stephan Nolting. All rights reserved. # */
/* # # */
/* # Redistribution and use in source and binary forms, with or without modification, are # */
/* # permitted provided that the following conditions are met: # */
/* # # */
/* # 1. Redistributions of source code must retain the above copyright notice, this list of # */
/* # conditions and the following disclaimer. # */
/* # # */
/* # 2. Redistributions in binary form must reproduce the above copyright notice, this list of # */
/* # conditions and the following disclaimer in the documentation and/or other materials # */
/* # provided with the distribution. # */
/* # # */
/* # 3. Neither the name of the copyright holder nor the names of its contributors may be used to # */
/* # endorse or promote products derived from this software without specific prior written # */
/* # permission. # */
/* # # */
/* # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS # */
/* # OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF # */
/* # MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE # */
/* # COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, # */
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/* # NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED # */
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/* # ********************************************************************************************* # */
/* # The NEORV32 Processor - https://github.com/stnolting/neorv32 (c) Stephan Nolting # */
/* ################################################################################################# */
// debug memory address map
.equ DBMEM_CODE_BASE, 0xfffff800 // base address of dbmem.code_memory
.equ DBMEM_PBUF_BASE, 0xfffff880 // base address of dbmem.program_buffer
.equ DBMEM_DBUF_BASE, 0xfffff900 // base address of dbmem.data_buffer
.equ DBMEM_SREG_BASE, 0xfffff980 // base address of dbmem.status_register
// status register (SREG) bits
.equ SREG_HALTED_ACK, (1<<0) // -/w: CPU is halted in debug mode and waits in park loop
.equ SREG_RESUME_REQ, (1<<1) // r/-: DM requests CPU to resume
.equ SREG_RESUME_ACK, (1<<2) // -/w: CPU starts resuming
.equ SREG_EXECUTE_REQ, (1<<3) // r/-: DM requests to execute program buffer
.equ SREG_EXECUTE_ACK, (1<<4) // -/w: CPU starts to execute program buffer
.equ SREG_EXCEPTION_ACK, (1<<5) // -/w: CPU has detected an exception
.file "park_loop.S"
.section .text
.balign 4
.option norvc
.global _start
.global entry_normal
.global entry_exception
_start:
// BASE + 0: entry for ebreak in debug-mode, halt request or return from single-stepped instruction
entry_normal:
jal zero, parking_loop_start
// BASE + 4: entry for exceptions - signal EXCEPTION to DM and restart parking loop
entry_exception:
csrw dscratch0, s0 // save s0 to dscratch0 so we have a general purpose register available
addi s0, zero, SREG_EXCEPTION_ACK // mask exception acknowledge flag
sw s0, DBMEM_SREG_BASE(zero) // trigger exception acknowledge to inform DM
csrr s0, dscratch0 // restore s0 from dscratch0
ebreak // restart parking loop
// "parking loop": endless loop that polls the status register to check if the DM
// wants to execute code from the program buffer or to resume normal CPU/application operation
parking_loop_start:
csrw dscratch0, s0 // save s0 to dscratch0 so we have a general purpose register available
addi s0, zero, SREG_HALTED_ACK
sw s0, DBMEM_SREG_BASE(zero) // ACK that CPU has halted
parking_loop:
lw s0, DBMEM_SREG_BASE(zero) // get status register
andi s0, s0, SREG_EXECUTE_REQ // request to execute program buffer?
bnez s0, execute_progbuf // execute program buffer
lw s0, DBMEM_SREG_BASE(zero) // get status register
andi s0, s0, SREG_RESUME_REQ // request to resume?
bnez s0, resume // resume normal operation
jal zero, parking_loop // restart parking loop polling
// resume normal operation
resume:
addi s0, zero, SREG_RESUME_ACK
sw s0, DBMEM_SREG_BASE(zero) // ACK that CPU is about to resume
csrr s0, dscratch0 // restore s0 from dscratch0
dret // end debug mode
// execute program buffer
execute_progbuf:
addi s0, zero, SREG_EXECUTE_ACK
sw s0, DBMEM_SREG_BASE(zero) // ACK that execution is about to start
csrr s0, dscratch0 // restore s0 from dscratch0
fence.i // synchronize i-cache & prefetch with memory (program buffer)
jalr zero, zero, %lo(DBMEM_PBUF_BASE) // jump to beginning of program buffer
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