SSI hard minimum preventing blockchain stalls when the timelord perfo…

…rmance is too low

bpx/consensus/constants.py

@@ -21,6 +21,7 @@ class ConsensusConstants:
     NUM_SPS_SUB_SLOT: uint32  # The number of signage points per sub-slot (including the 0th sp at the sub-slot start)
 
     SUB_SLOT_ITERS_STARTING: uint64  # The sub_slot_iters for the first epoch
+    SUB_SLOT_ITERS_HARD_MIN: uint64  # Hard minimum for anti-stall protection
     DIFFICULTY_CONSTANT_FACTOR: uint128  # Multiplied by the difficulty to get iterations
     DIFFICULTY_STARTING: uint64  # The difficulty for the first epoch
     # The maximum factor by which difficulty and sub_slot_iters can change per epoch

bpx/consensus/default_constants.py

@@ -10,6 +10,7 @@
     "MAX_SUB_SLOT_BLOCKS": 128,  # Must be less than half of SUB_EPOCH_BLOCKS
     "NUM_SPS_SUB_SLOT": 64,  # Must be a power of 2
     "SUB_SLOT_ITERS_STARTING": 2**20,
+    "SUB_SLOT_ITERS_HARD_MIN": 2**19,
     # DIFFICULTY_STARTING is the starting difficulty for the first epoch, which is then further
     # multiplied by another factor of DIFFICULTY_CONSTANT_FACTOR, to be used in the VDF iter calculation formula.
     "DIFFICULTY_CONSTANT_FACTOR": 2**51,

bpx/consensus/difficulty_adjustment.py

@@ -257,7 +257,7 @@ def _get_next_sub_slot_iters(
     if new_ssi_precise >= last_block_curr.sub_slot_iters:
         new_ssi_precise = uint64(min(new_ssi_precise, max_ssi))
     else:
-        new_ssi_precise = uint64(max([constants.NUM_SPS_SUB_SLOT, new_ssi_precise, min_ssi]))
+        new_ssi_precise = uint64(max([constants.SUB_SLOT_ITERS_HARD_MIN, new_ssi_precise, min_ssi]))
 
     new_ssi = truncate_to_significant_bits(new_ssi_precise, constants.SIGNIFICANT_BITS)
     new_ssi = uint64(new_ssi - new_ssi % constants.NUM_SPS_SUB_SLOT)  # Must divide the sub slot