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// See LICENSE.SiFive for license details.
#include "riscv/encoding.h"
#include "riscv/debug_rom_defines.h"
.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:
// Not used.
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_DSCRATCH0, 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, DEBUG_ROM_HALTED(zero)
lbu s0, DEBUG_ROM_FLAGS(s0) // 1 byte flag per hart. Only one hart advances here.
andi s0, s0, (1 << DEBUG_ROM_FLAG_GO)
bnez s0, going
csrr s0, CSR_MHARTID
lbu s0, DEBUG_ROM_FLAGS(s0) // multiple harts can resume here
andi s0, s0, (1 << DEBUG_ROM_FLAG_RESUME)
bnez s0, _resume
wfi
jal zero, entry_loop
_exception:
// Restore S0, which we always save to dscratch.
// We need this in case the user tried an abstract write to a
// non-existent CSR.
csrr s0, CSR_DSCRATCH0
sw zero, DEBUG_ROM_EXCEPTION(zero) // Let debug module know you got an exception.
ebreak
going:
csrr s0, CSR_MHARTID
sw s0, DEBUG_ROM_GOING(zero) // When debug module sees this write, the GO flag is reset.
csrr s0, CSR_DSCRATCH0 // Restore s0 here
fence
fence.i
jalr zero, zero, %lo(whereto) // Debug module will put different instructions and data in the RAM,
// so we use fence and fence.i for safety. (rocket-chip doesn't have this
// because jalr is special there)
_resume:
csrr s0, CSR_MHARTID
sw s0, DEBUG_ROM_RESUMING(zero) // When Debug Module sees this write, the RESUME flag is reset.
csrr s0, CSR_DSCRATCH0 // 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.
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