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rocket-chip/scripts/debug_rom/debug_rom.S

77 lines
2.8 KiB
ArmAsm
Executable File

// 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 OK_GO 0x400
.option norvc
.global entry
.global exception
// Entry location on ebreak, Halt, or Breakpoint
// It is the same for all harts. They branch when
// their specific OK_GO 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 not be halted anymore.
entry_loop:
csrr s0, CSR_MHARTID
sw s0, HALTED(zero)
lb s0, OK_GO(s0) // 1 byte flag per hart. Only one hart advances here.
bne zero, s0, going
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 OK_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:
csrw CSR_DSCRATCH, s0 // Save s0 to allow signaling MHARTID
csrr s0, CSR_MHARTID
sw s0, RESUMING(zero) // Let the Debug Module know you're not halted anymore.
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.