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✨ Add SiFive debug rom
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zarubaf committed Jul 10, 2018
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202 changes: 202 additions & 0 deletions LICENSE.SiFive
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Copyright 2016-2017 SiFive, Inc.

Licensed under the Apache License, Version 2.0 (the "License");
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31 changes: 31 additions & 0 deletions src/debug/debug_rom/Makefile
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# See LICENSE.SiFive for license details
# Recursive make is bad, but in this case we're cross compiling which is a
# pretty unusual use case.

CC = $(RISCV)/bin/riscv64-unknown-elf-gcc
OBJCOPY = $(RISCV)/bin/riscv64-unknown-elf-objcopy

COMPILE = $(CC) -nostdlib -nostartfiles -I$(RISCV)/include/ -Tlink.ld

ELFS = debug_rom
DEPS = debug_rom.S link.ld

all: $(patsubst %,%.h,$(ELFS))

publish: debug_rom.scala
mv $< ../../src/main/scala/uncore/devices/debug/DebugRomContents.scala

%.scala: %.raw
xxd -i $^ | sed -e "s/^unsigned char debug_rom_raw\[\] = {/\/\/ This file was auto-generated by 'make publish' in debug\/ directory.\n\npackage uncore.devices\n\nobject DebugRomContents {\n\n def apply() : Array[Byte] = { Array (/" \
-e "s/};/ ).map(_.toByte) }\n\n}/" \
-e "s/^unsigned int debug_rom_raw_len.*//" > $@


%.raw: %
$(OBJCOPY) -O binary --only-section .text $^ $@

debug_rom: $(DEPS)
$(COMPILE) -o $@ $^

clean:
rm -f $(ELFS) debug_rom*.raw debug_rom*.h
81 changes: 81 additions & 0 deletions src/debug/debug_rom/debug_rom.S
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// See LICENSE.SiFive for license details.

#include "spike/encoding.h"

// These are implementation-specific addresses in the Debug Module
#define HALTED 0x100
#define GOING 0x104
#define RESUMING 0x108
#define EXCEPTION 0x10C

// Region of memory where each hart has 1
// byte to read.
#define FLAGS 0x400
#define FLAG_GO 0
#define FLAG_RESUME 1

.option norvc
.global entry
.global exception

// Entry location on ebreak, Halt, or Breakpoint
// It is the same for all harts. They branch when
// their GO or RESUME bit is set.

entry:
jal zero, _entry
resume:
jal zero, _resume
exception:
jal zero, _exception

_entry:
// This fence is required because the execution may have written something
// into the Abstract Data or Program Buffer registers.
fence
csrw CSR_DSCRATCH, s0 // Save s0 to allow signaling MHARTID

// We continue to let the hart know that we are halted in order that
// a DM which was reset is still made aware that a hart is halted.
// We keep checking both whether there is something the debugger wants
// us to do, or whether we should resume.
entry_loop:
csrr s0, CSR_MHARTID
sw s0, HALTED(zero)
lbu s0, FLAGS(s0) // 1 byte flag per hart. Only one hart advances here.
andi s0, s0, (1 << FLAG_GO)
bnez s0, going
csrr s0, CSR_MHARTID
lbu s0, FLAGS(s0) // multiple harts can resume here
andi s0, s0, (1 << FLAG_RESUME)
bnez s0, resume
jal zero, entry_loop

_exception:
sw zero, EXCEPTION(zero) // Let debug module know you got an exception.
ebreak

going:
csrr s0, CSR_DSCRATCH // Restore s0 here
sw zero, GOING(zero) // When debug module sees this write, the GO flag is reset.
jalr zero, zero, %lo(whereto) // Rocket-Chip has a specific hack which is that jalr in
// Debug Mode will flush the I-Cache. We need that so that the
// remainder of the variable instructions will be what Debug Module
// intends.
_resume:
csrr s0, CSR_MHARTID
sw s0, RESUMING(zero) // When Debug Module sees this write, the RESUME flag is reset.
csrr s0, CSR_DSCRATCH // Restore s0
dret

// END OF ACTUAL "ROM" CONTENTS. BELOW IS JUST FOR LINKER SCRIPT.

.section .whereto
whereto:
nop
// Variable "ROM" This is : jal x0 abstract, jal x0 program_buffer,
// or jal x0 resume, as desired.
// Debug Module state machine tracks what is 'desired'.
// We don't need/want to use jalr here because all of the
// Variable ROM contents are set by
// Debug Module before setting the OK_GO byte.
16 changes: 16 additions & 0 deletions src/debug/debug_rom/link.ld
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/* See LICENSE.SiFive for license details. */
OUTPUT_ARCH( "riscv" )
ENTRY( entry )
SECTIONS
{
.whereto 0x300 :
{
*(.whereto)
}
. = 0x800;
.text :
{
*(.text)
}
_end = .;
}

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