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esp32: Add "Free RAM" optimisation config flags.

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This is necessary for ESP32-C2 Wi-Fi & BT to work reliably (and for TLS to
work at all). On IDF 5.4.2 the free static RAM goes from 60KB to 100KB, and
there will also be a reduction in lwIP & Wi-Fi memory use at runtime.

The performance trade-off seems low for most use cases, although it will
probably be significant for certain combinations of load (i.e. heavy
TCP/IP, heavy BT throughput, and some peripheral driver functions).

Added as a set of config flags because this is potentially useful on other
SoCs where the goal is to maximise RAM available for MicroPython.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>
This commit is contained in:
Angus Gratton
2025-07-25 13:22:00 +10:00
parent ca9916968c
commit 77c9eb7795
2 changed files with 46 additions and 0 deletions
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2
ports/esp32/boards/ESP32_GENERIC_C2/mpconfigboard.cmake
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@@ -4,4 +4,6 @@ set(SDKCONFIG_DEFAULTS
boards/sdkconfig.base
boards/sdkconfig.ble
boards/sdkconfig.c2
# C2 has unusably low free RAM without these optimisations
boards/sdkconfig.free_ram
)

44
ports/esp32/boards/sdkconfig.free_ram Normal file
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@@ -0,0 +1,44 @@
# This is a collection of sdkconfig settings that frees RAM at runtime,
# at the expense of performance.
#
# Not all options will work on all SoC families, but adding this sdkconfig
# set to a board should increase the free memory.
#
# - Many options free IRAM, which on most ESP32 families leads to
# free DRAM at runtime (original ESP32 and S2 may not).
# - The other options reduce runtime DRAM usage from the heap.
#
# IMPORTANT: If you enable these config settings on a custom build then you may
# encounter bugs or crashes. If you choose to open a MicroPython bug report then
# please mention these config settings!
# Place functions in flash whenever possible to free IRAM
CONFIG_RINGBUF_PLACE_FUNCTIONS_INTO_FLASH=y
CONFIG_FREERTOS_PLACE_FUNCTIONS_INTO_FLASH=y
CONFIG_HEAP_PLACE_FUNCTION_INTO_FLASH=y
# Use the SPI flash functions in ROM (when available). This may limit flash chip
# support and cause issues with some flash chips. Each SoC family has different
# set of chip support baked into ROM.
CONFIG_SPI_FLASH_ROM_IMPL=y
# Run the Bluetooth controller from flash not IRAM
CONFIG_BT_CTRL_RUN_IN_FLASH_ONLY=y
# lwIP adjustments to limit runtime memory usage (at expense of performance, and/or
# a reduction in number of active connections).
CONFIG_LWIP_TCPIP_RECVMBOX_SIZE=16
CONFIG_LWIP_MAX_SOCKETS=6
CONFIG_LWIP_MAX_ACTIVE_TCP=8
# These lwIP values are recommended to scale relative to the Wi-Fi buffer numbers
CONFIG_LWIP_TCP_WND_DEFAULT=3072
CONFIG_LWIP_TCP_SND_BUF_DEFAULT=3072
# Wi-Fi adjustments to reduce peak runtime memory usage, at expense of peak
# performance
CONFIG_ESP_WIFI_STATIC_RX_BUFFER_NUM=8
CONFIG_ESP_WIFI_DYNAMIC_RX_BUFFER_NUM=12
CONFIG_ESP_WIFI_DYNAMIC_TX_BUFFER_NUM=12
CONFIG_ESP_WIFI_RX_MGMT_BUF_NUM_DEF=2
CONFIG_ESP_WIFI_RX_BA_WIN=12