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[sw/ocd-firmware] optimize park-loop

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faster debugging response
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stnolting 2022-12-16 17:39:37 +01:00
parent ba2fc9701f
commit 5095a0072a
3 changed files with 29 additions and 51 deletions
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22
sw/ocd-firmware/README.md
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@ -1,18 +1,20 @@
# NEORV32 On-Chip Debugger (OCD) - "Park Loop" Code
# NEORV32 On-Chip Debugger (OCD) - "Park Loop" Code (Firmware)
This folder contains the ASM sources for the *execution-based* debugger code ROM.
`park_loop.S` contains the "park loop" that is executed when the CPU is in debug mode. This code is used to communicate
with the *debug module (DM)* and is responsible for:
This folder contains the source code for the *execution-based* debugger code ROM (firmware).
`park_loop.S` contains the "park loop" that is executed when the CPU is in debug mode. This code
is used to communicate with the *debug module (DM)* and is responsible for:
* acknowledging halt requests
* processing and acknowledging resume requests
* processing and acknowledging "execute program buffer" requests
* executing the program buffer (provided by the DM)
* catching exceptions while in debug mode
* catching and acknowledging exceptions while in debug mode
The park loop code is implemented as endless loop that polls the status register of the *debug memory (DBMEM)* module
to check for requests from the DM and sets according flags in the status register to acknowledge these requests.
The park loop code is implemented as endless loop that polls the status register of
the _debug memory (DM)_ module to check for requests from the DM and sets according flags in the
status register to acknowledge these requests.
:warning: Executing `make clean_all all` will **NOT** update the actual debugger code ROM that will be synthesized.
The interface with the DM will break if there are any bugs in this code. However, if you wish to update the code ROM,
copy the array content from `neorv32_debug_mem.code.vhd` to the `code_rom_file` constant in `rtl/core/neorv32_debug_dbmem.vhd`.
:warning: Executing `make clean_all all` will **NOT** update the actual debugger code ROM that
will be synthesized. The interface with the DM will break if there are any bugs in this code.
However, if you wish to update the code ROM, copy the array content from `neorv32_debug_mem.code.vhd`
to the `code_rom_file` constant in `rtl/core/neorv32_debug_dm.vhd`.

24
sw/ocd-firmware/debug_rom.ld
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@ -1,7 +1,7 @@
/* ################################################################################################# */
/* # << NEORV32 - RISC-V GCC Linker Script >> # */
/* # ********************************************************************************************* # */
/* # For the execution based on-chip debugger code memory (/ROM() - "park loop" code # */
/* # For the execution-based on-chip debugger code memory (/ROM() - "park loop" code (firmware) # */
/* # ********************************************************************************************* # */
/* # BSD 3-Clause License # */
/* # # */
@ -34,37 +34,19 @@
/* # The NEORV32 Processor - https://github.com/stnolting/neorv32 (c) Stephan Nolting # */
/* ################################################################################################# */
/* Default linker script, for normal executables */
/* Copyright (C) 2014-2020 Free Software Foundation, Inc.
Copying and distribution of this script, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved. */
/* modified for the NEORV32 processor by Stephan Nolting */
OUTPUT_FORMAT("elf32-littleriscv")
OUTPUT_ARCH(riscv)
ENTRY(_start)
SEARCH_DIR("/opt/riscv/riscv32-unknown-elf/lib")
SEARCH_DIR("=/usr/local/lib")
SEARCH_DIR("=/lib")
SEARCH_DIR("=/usr/lib")
ENTRY(__start)
MEMORY
{
debug_mem (rx) : ORIGIN = 0xFFFFF800, LENGTH = 128
debug_mem (rx) : ORIGIN = 0xFFFFF800, LENGTH = 128
}
/* ************************************************************************* */
SECTIONS
{
/* Actual instructions */
.text :
{
KEEP(*(.text));
} > debug_mem
}

34
sw/ocd-firmware/park_loop.S
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@ -1,9 +1,9 @@
/* ################################################################################################# */
/* # << NEORV32 - park_loop.S - Execution-Based On-Chip Debugger - Park Loop Code >> # */
/* # << NEORV32 - park_loop.S - Execution-Based On-Chip Debugger Firmware - Park Loop Code >> # */
/* # ********************************************************************************************* # */
/* # BSD 3-Clause License # */
/* # # */
/* # Copyright (c) 2021, Stephan Nolting. All rights reserved. # */
/* # Copyright (c) 2022, 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: # */
@ -50,42 +50,36 @@
.section .text
.balign 4
.option norvc
.global _start
.global entry_normal
.global __start
.global entry_exception
.global entry_normal
__start:
_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
// BASE + 0: 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
addi s0, zero, SREG_EXCEPTION_ACK // set 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
jal zero, parking_loop_halt // start parking loop
// BASE + 16: entry for ebreak in debug-mode, halt request or return from single-stepped instruction
// "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:
entry_normal:
csrw dscratch0, s0 // save s0 to dscratch0 so we have a general purpose register available
parking_loop_halt:
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
bnez s0, execute // 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
beqz s0, parking_loop // no: restart parking loop; yes: resume normal operation
// resume normal operation
resume:
@ -95,7 +89,7 @@ resume:
dret // end debug mode
// execute program buffer
execute_progbuf:
execute:
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