[otbnsim] Refactor loop address handling
The loop code deals with various instruction addresses. Introduce a
couple helper functions and use them to make the semantics and
relationships between them easier to understand.
Signed-off-by: Philipp Wagner <phw@lowrisc.org>
diff --git a/hw/ip/otbn/dv/otbnsim/sim/loop.py b/hw/ip/otbn/dv/otbnsim/sim/loop.py
index a21c389..2f8455c 100644
--- a/hw/ip/otbn/dv/otbnsim/sim/loop.py
+++ b/hw/ip/otbn/dv/otbnsim/sim/loop.py
@@ -33,7 +33,8 @@
start_addr is the first instruction inside the loop (the instruction
following the loop instruction). insn_count is the number of instructions
in the loop (and must be positive). restarts is one less than the number of
- iterations, and must be non-negative.
+ iterations, and must be non-negative. last_addr is the address of the last
+ instruction in the loop body.
'''
def __init__(self, start_addr: int, insn_count: int, restarts: int):
@@ -44,7 +45,12 @@
self.loop_count = 1 + restarts
self.restarts_left = restarts
self.start_addr = start_addr
- self.match_addr = start_addr + 4 * insn_count
+ self.last_addr = start_addr + 4 * insn_count - 4
+
+ def get_loop_insn_addr(self) -> int:
+ '''The address of the LOOP or LOOPI instruction.'''
+ assert self.start_addr >= 4
+ return self.start_addr - 4
class LoopStack:
@@ -83,37 +89,44 @@
self.trace.append(TraceLoopStart(loop_count, insn_count))
self.stack.append(LoopLevel(start_addr, insn_count, loop_count - 1))
+ def is_last_insn_in_loop_body(self, pc: int) -> bool:
+ '''Is pc the last instruction address the current loop body?'''
+
+ if not self.stack:
+ return False
+
+ top = self.stack[-1]
+ return pc == top.last_addr
+
def check_insn(self, pc: int, insn_affects_control: bool) -> None:
'''Check for branch instructions at the end of a loop body'''
- if self.stack:
- top = self.stack[-1]
- if pc + 4 == top.match_addr:
- # We're about to execute the last instruction in the loop body.
- # Make sure that it isn't a jump, branch or another loop
- # instruction.
- if insn_affects_control:
- self.err_flag = True
+ if self.is_last_insn_in_loop_body(pc) and insn_affects_control:
+ # We're about to execute the last instruction in the loop body.
+ # Make sure that it isn't a jump, branch or another loop
+ # instruction.
+ self.err_flag = True
- def step(self, next_pc: int) -> Optional[int]:
+ def step(self, pc: int) -> Optional[int]:
'''Update loop stack. If we should loop, return new PC'''
- if self.stack:
+
+ if self.is_last_insn_in_loop_body(pc):
+ assert self.stack
top = self.stack[-1]
- if next_pc == top.match_addr:
- assert top.restarts_left >= 0
+ assert top.restarts_left >= 0
- # 1-based iteration number
- loop_idx = top.loop_count - top.restarts_left
+ # 1-based iteration number
+ loop_idx = top.loop_count - top.restarts_left
- if not top.restarts_left:
- self.stack.pop()
- ret_val = None
- else:
- top.restarts_left -= 1
- ret_val = top.start_addr
+ if not top.restarts_left:
+ self.stack.pop()
+ ret_val = None
+ else:
+ top.restarts_left -= 1
+ ret_val = top.start_addr
- self.trace.append(TraceLoopIteration(loop_idx, top.loop_count))
- return ret_val
+ self.trace.append(TraceLoopIteration(loop_idx, top.loop_count))
+ return ret_val
return None
diff --git a/hw/ip/otbn/dv/otbnsim/sim/state.py b/hw/ip/otbn/dv/otbnsim/sim/state.py
index 325991f..2036049 100644
--- a/hw/ip/otbn/dv/otbnsim/sim/state.py
+++ b/hw/ip/otbn/dv/otbnsim/sim/state.py
@@ -69,7 +69,7 @@
self.loop_stack.start_loop(next_pc, iterations, bodysize)
def loop_step(self) -> None:
- back_pc = self.loop_stack.step(self.pc + 4)
+ back_pc = self.loop_stack.step(self.pc)
if back_pc is not None:
self.pc_next = back_pc
