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Cortex-m App Flashing: Ordering and Padding Improvements #128

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Cortex-m App Flashing: Ordering and Padding Improvements #128

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e34119f
app_tab: use subregions for cortex-m apps >64kB
tyler-potyondy Jan 15, 2026
8eb9aa4
Ascending app flash order for cortex-m
tyler-potyondy Jan 15, 2026
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33 changes: 29 additions & 4 deletions tockloader/app_tab.py
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
import logging
import math
import struct
import textwrap

Expand Down Expand Up @@ -166,16 +167,40 @@ def set_size_constraint(self, constraint):
# Make sure the total app size is a power of two.
for tbf in self._get_tbfs():
current_size = tbf.tbfh.get_app_size()
original_app_size = current_size
if (current_size & (current_size - 1)) != 0:
# This is not a power of two, but should be.
count = 0
while current_size != 0:
current_size >>= 1
count += 1
tbf.tbfh.set_app_size(1 << count)
logging.debug(
"Rounding app up to ^2 size ({} bytes)".format(1 << count)
)

# Use 64kB as a heuristic for packing. Use the next power
# of two for sizes less than 64kB. Otherwise we use the
# the following to reduce wasted space:
# (X - 1) * (NextPowerOfTwo / 8) < size < X * (NextPowerOfTwo)
if original_app_size < (1024 * 64):
logging.debug(
"Rounding app up to ^2 size ({} bytes)".format(1 << count)
)
tbf.tbfh.set_app_size(1 << count)
else:
next_power2 = 1 << count
# Arm cortex-m v7 has 8 subregions for each MPU region
# of equal size, so we can enable X subregions of size
# 2^N / 8.
multiple = next_power2 / 8
number_of_unmasked_subregions = math.ceil(
original_app_size / multiple
)
new_size = int(number_of_unmasked_subregions * multiple)
logging.debug(
"Rounding app up to (X - 1) * (NextPowerOfTwo / 8) \
< size < X * (NextPowerOfTwo) ({} bytes)".format(
new_size
)
)
tbf.tbfh.set_app_size(new_size)

elif type(constraint) is tuple:
if constraint[0] == "multiple":
Expand Down
6 changes: 4 additions & 2 deletions tockloader/tockloader.py
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Original file line number Diff line number Diff line change
Expand Up @@ -76,7 +76,7 @@ class TockLoader:
# - `start_address`: The absolute address in flash where apps start and
# must be loaded.
# - `order`: How apps should be sorted when flashed onto the board.
# Supported values: size_descending, None
# Supported values: size_descending, size_ascending, None
# - `size_constraint`: Valid sizes for the entire application.
# Supported values: powers_of_two, (multiple, value),
# None
Expand All @@ -94,7 +94,7 @@ class TockLoader:
},
"arch": {
"cortex-m": {
"order": "size_descending",
"order": "size_ascending",
"size_constraint": "powers_of_two",
"alignment_constraint": "size",
}
Expand Down Expand Up @@ -1561,6 +1561,8 @@ def is_valid(slices):
pass
elif self.app_settings["order"] == "size_descending":
apps.sort(key=lambda app: app.get_size(), reverse=True)
elif self.app_settings["order"] == "size_ascending":
apps.sort(key=lambda app: app.get_size())
elif self.app_settings["order"] == None:
# Any order is fine.
pass
Expand Down