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# This code should be functional. Doesn't have to be optimal.
# I'm writing it to prove that it can be done.
#include "riscv/encoding.h"
# TODO: Update these constants once they're finalized in the doc.
#define DCSR 0x790
#define DCSR_CAUSE_DEBINT 3
#define DCSR_HALT_OFFSET 3
#define DCSR_DEBUGINT_OFFSET 10
#define DSCRATCH 0x792
#define DEBUG_RAM 0x400
#define DEBUG_RAM_SIZE 64
#define SETHALTNOT 0x100
#define CLEARDEBINT 0x108
.global entry
.global resume
.global exception
# Automatically called when Debug Mode is first entered.
entry: j _entry
# Should be called by Debug RAM code that has finished execution and
# wants to return to Debug Mode.
resume:
j _resume
exception:
# Set the last word of Debug RAM to all ones, to indicate that we hit
# an exception.
li s0, ~0
j _resume2
_resume:
li s0, 0
_resume2:
# Clear debug interrupt.
csrr s1, CSR_MHARTID
sw s1, CLEARDEBINT(zero)
fence
# Restore s1.
csrr s1, CSR_MISA
bltz s1, restore_not_32
restore_32:
lw s1, (DEBUG_RAM + DEBUG_RAM_SIZE - 4)(zero)
j check_halt
restore_not_32:
slli s1, s1, 1
bltz s1, restore_128
restore_64:
ld s1, (DEBUG_RAM + DEBUG_RAM_SIZE - 8)(zero)
j check_halt
restore_128:
nop #lq s1, (DEBUG_RAM + DEBUG_RAM_SIZE - 16)(zero)
# s0 contains ~0 if we got here through an exception, and 0 otherwise.
# Store this to the last word in Debug RAM so the debugger can tell if
# an exception occurred.
sw s0, (DEBUG_RAM + DEBUG_RAM_SIZE - 4)(zero)
check_halt:
csrr s0, DCSR
andi s0, s0, (1<<DCSR_HALT_OFFSET)
beqz s0, exit
j wait_for_interrupt
exit:
# Restore s0.
csrr s0, DSCRATCH
dret
_entry:
# Save s0 in DSCRATCH
csrw DSCRATCH, s0
# Check why we're here
csrr s0, DCSR
# cause is in bits 2:0 of dcsr
andi s0, s0, 7
addi s0, s0, -DCSR_CAUSE_DEBINT
bnez s0, spontaneous_halt
jdebugram:
# Save s1 so that the debug program can use two registers.
fence.i
csrr s0, CSR_MISA
bltz s0, save_not_32
save_32:
sw s1, (DEBUG_RAM + DEBUG_RAM_SIZE - 4)(zero)
jr zero, DEBUG_RAM
save_not_32:
slli s0, s0, 1
bltz s0, save_128
save_64:
sd s1, (DEBUG_RAM + DEBUG_RAM_SIZE - 8)(zero)
jr zero, DEBUG_RAM
save_128:
nop #sq s1, (DEBUG_RAM + DEBUG_RAM_SIZE - 16)(zero)
jr zero, DEBUG_RAM
spontaneous_halt:
csrr s0, CSR_MHARTID
sw s0, SETHALTNOT(zero)
csrsi DCSR, (1<<DCSR_HALT_OFFSET)
wait_for_interrupt:
csrr s0, DCSR
andi s0, s0, (1<<DCSR_DEBUGINT_OFFSET)
beqz s0, wait_for_interrupt
j jdebugram
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