Can we reduce ESP IDF boiler plate size? - c

Question

I tested running bare bones code using ESP IDF on an ESP32 chip using duinotech XC-3800, and obtained the following results in terms of image size.
Analysis Binary Size for ESP32
Folder Structure
temp/
main/
CMakeLists.txt
main.c
CMakeLists.txt
File contents
CMakeLists.txt
# The following lines of boilerplate have to be in your project's
# CMakeLists in this exact order for cmake to work correctly
cmake_minimum_required(VERSION 3.5)
include($ENV{IDF_PATH}/tools/cmake/project.cmake)
project(temp)
main>CMakeLists.txt
idf_component_register(SRCS "main.c"
INCLUDE_DIRS "")
Test 1 main>main.c
#include <stdio.h>
void app_main(void) {
printf("Hello world!\n");
for (int i = 10; i >= 0; i--) {
printf("Restarting in %d seconds...\n", i);
}
printf("Restarting now.\n");
fflush(stdout);
}
Test 2 main>main.c
#include <stdio.h>
void app_main(void) { printf("Hello world!\n"); }
Test 3 main>main.c
void app_main(void) {}
Size comparison
Obtained by running idf_size.py build/temp.map
Test 1
Total sizes:
DRAM .data size: 8320 bytes
DRAM .bss size: 4072 bytes
Used static DRAM: 12392 bytes ( 168344 available, 6.9% used)
Used static IRAM: 38804 bytes ( 92268 available, 29.6% used)
Flash code: 75408 bytes
Flash rodata: 23844 bytes
Total image size:~ 146376 bytes (.bin may be padded larger)
Test 2
Total sizes:
DRAM .data size: 8320 bytes
DRAM .bss size: 4072 bytes
Used static DRAM: 12392 bytes ( 168344 available, 6.9% used)
Used static IRAM: 38804 bytes ( 92268 available, 29.6% used)
Flash code: 75240 bytes
Flash rodata: 23796 bytes
Total image size:~ 146160 bytes (.bin may be padded larger)
Test 3
Total sizes:
DRAM .data size: 8320 bytes
DRAM .bss size: 4072 bytes
Used static DRAM: 12392 bytes ( 168344 available, 6.9% used)
Used static IRAM: 38804 bytes ( 92268 available, 29.6% used)
Flash code: 75004 bytes
Flash rodata: 23780 bytes
Total image size:~ 145908 bytes (.bin may be padded larger)
Analysis
Size for code obtained by running stat --format="%s" main/main.c
All Sizes are in Bytes
Test No. | Code | Image | Flash Code | Flash rodata
-------- | -----| ------ | ---------- | ------------
1 | 207 | 146376 | 75408 | 23844
2 | 70 | 146160 | 75240 | 23796
3 | 43 | 145908 | 75004 | 23780
At least 145KB of boiler plate code just to get an empty main run.
Speculation
I suspect that the 145KB is made up of a number of libraries that are always loaded onto the chip whether you use them or not. Some of them must be the FreeRTOS, WiFi, HTTP etc.
Can we bring down this size somehow and load only the bare minimum required for operation?

Answer 1

You can get more detailed size information by running idf.py size-components and idf.py size-files. Here are the results for your "Test 3" (i.e. empty function) on my dev environment (note that my Total Image Size is already slightly larger than the one you posted.
Total sizes:
DRAM .data size: 7860 bytes
DRAM .bss size: 4128 bytes
Used static DRAM: 11988 bytes ( 168748 available, 6.6% used)
Used static IRAM: 32706 bytes ( 98366 available, 25.0% used)
Flash code: 76002 bytes
Flash rodata: 32164 bytes
Total image size:~ 148732 bytes (.bin may be padded larger)
Per-archive contributions to ELF file:
Archive File DRAM .data & .bss IRAM Flash code & rodata Total
libc.a 0 0 0 55348 3829 59177
libesp32.a 2132 2351 6767 5976 8076 25302
libfreertos.a 4140 776 12432 0 1653 19001
libdriver.a 76 20 0 4003 7854 11953
libsoc.a 161 4 4953 612 3852 9582
libvfs.a 240 103 0 5464 950 6757
libheap.a 877 4 3095 830 986 5792
libspi_flash.a 24 290 1855 779 890 3838
libefuse.a 16 4 0 1142 2213 3375
libnewlib.a 152 272 766 830 96 2116
libapp_update.a 0 4 109 159 1221 1493
libesp_ringbuf.a 0 0 848 0 209 1057
liblog.a 8 268 429 82 0 787
libhal.a 0 0 515 0 32 547
libpthread.a 8 12 0 256 0 276
libgcc.a 0 0 0 0 160 160
libbootloader_support.a 0 0 0 126 0 126
libm.a 0 0 0 88 0 88
libcxx.a 0 0 0 11 0 11
libxtensa-debug-module.a 0 0 8 0 0 8
libmain.a 0 0 0 5 0 5
(exe) 0 0 0 0 0 0
libmbedcrypto.a 0 0 0 0 0 0
libmbedtls.a 0 0 0 0 0 0
libwpa_supplicant.a 0 0 0 0 0 0
Per-file contributions to ELF file:
Object File DRAM .data & .bss IRAM Flash code & rodata Total
lib_a-vfprintf.o 0 0 0 14193 756 14949
lib_a-svfprintf.o 0 0 0 13838 756 14594
lib_a-svfiprintf.o 0 0 0 9642 1210 10852
lib_a-vfiprintf.o 0 0 0 9945 738 10683
uart.c.obj 44 12 0 2985 7293 10334
tasks.c.obj 12 700 5546 0 531 6789
vfs_uart.c.obj 48 63 0 3680 808 4599
panic.c.obj 2023 5 1989 0 0 4017
esp_err_to_name.c.obj 0 0 0 50 3947 3997
portasm.S.obj 3084 0 484 0 0 3568
lib_a-dtoa.o 0 0 0 3522 13 3535
multi_heap.c.obj 873 0 2277 0 0 3150
intr_alloc.c.obj 8 22 618 1703 722 3073
esp_efuse_utility.c.obj 0 0 0 867 2205 3072
cpu_start.c.obj 0 1 1068 331 1352 2752
queue.c.obj 0 0 2310 0 325 2635
lib_a-mprec.o 0 0 0 2134 296 2430
rtc_clk.c.obj 161 4 2098 0 0 2263
dbg_stubs.c.obj 0 2072 32 108 0 2212
vfs.c.obj 192 40 0 1784 142 2158
rtc_periph.c.obj 0 0 0 0 2080 2080
esp_timer_esp32.c.obj 8 26 1068 262 538 1902
xtensa_vectors.S.obj 8 0 1776 0 36 1820
flash_mmap.c.obj 0 264 1092 114 339 1809
task_wdt.c.obj 53 4 0 1178 548 1783
heap_caps.c.obj 4 0 818 52 617 1491
timers.c.obj 8 56 1006 0 233 1303
cache_utils.c.obj 4 14 749 81 402 1250
soc_memory_layout.c.obj 0 0 0 0 1181 1181
heap_caps_init.c.obj 0 4 0 778 369 1151
port.c.obj 0 16 625 0 493 1134
esp_ota_ops.c.obj 0 4 0 147 965 1116
xtensa_intr_asm.S.obj 1024 0 51 0 0 1075
ringbuf.c.obj 0 0 848 0 209 1057
rtc_time.c.obj 0 0 815 0 198 1013
memory_layout_utils.c.ob 0 0 0 612 393 1005
rtc_init.c.obj 0 0 992 0 0 992
periph_ctrl.c.obj 8 0 0 615 280 903
lib_a-fseeko.o 0 0 0 866 0 866
time.c.obj 0 32 122 703 0 857
clk.c.obj 0 0 64 559 221 844
esp_timer.c.obj 8 16 261 406 134 825
dport_access.c.obj 8 40 444 189 137 818
log.c.obj 8 268 429 82 0 787
rtc_wdt.c.obj 0 0 743 0 0 743
partition.c.obj 0 8 0 522 149 679
ipc.c.obj 0 28 159 283 120 590
locks.c.obj 8 0 485 0 94 587
crosscore_int.c.obj 8 8 193 130 156 495
syscall_table.c.obj 144 240 0 82 0 466
system_api.c.obj 0 0 439 0 0 439
timer.c.obj 16 0 0 112 281 409
int_wdt.c.obj 0 1 91 306 0 398
freertos_hooks.c.obj 8 128 43 216 0 395
esp_app_desc.c.obj 0 0 109 12 256 377
brownout.c.obj 0 0 0 149 201 350
windowspill_asm.o 0 0 311 0 0 311
rtc_module.c.obj 8 8 0 291 0 307
xtensa_context.S.obj 0 0 306 0 0 306
cpu_util.c.obj 0 0 305 0 0 305
dport_panic_highint_hdl. 8 0 242 0 0 250
lib_a-reent.o 0 0 0 232 0 232
lib_a-fopen.o 0 0 0 224 0 224
lib_a-snprintf.o 0 0 0 214 0 214
esp_efuse_api.c.obj 0 4 0 193 0 197
pthread_local_storage.c. 8 4 0 180 0 192
cache_err_int.c.obj 0 0 56 98 0 154
xtensa_intr.c.obj 0 0 108 0 35 143
list.c.obj 0 0 142 0 0 142
syscalls.c.obj 0 0 91 45 0 136
lib_a-assert.o 0 0 0 68 60 128
lib_a-flags.o 0 0 0 127 0 127
bootloader_common.c.obj 0 0 0 126 0 126
lib_a-s_frexp.o 0 0 0 110 0 110
flash_ops.c.obj 20 4 14 62 0 100
lib_a-vprintf.o 0 0 0 94 0 94
lib_a-s_fpclassify.o 0 0 0 88 0 88
lib_a-fiprintf.o 0 0 0 84 0 84
pthread.c.obj 0 8 0 76 0 84
esp_efuse_fields.c.obj 0 0 0 82 0 82
clock.o 0 0 72 0 0 72
reent_init.c.obj 0 0 68 0 2 70
state_asm--restore_extra 0 0 62 0 0 62
state_asm--save_extra_nw 0 0 62 0 0 62
xtensa_vector_defaults.S 0 0 46 0 0 46
lib_a-fseek.o 0 0 0 45 0 45
_divdi3.o 0 0 0 0 40 40
_moddi3.o 0 0 0 0 40 40
_udivdi3.o 0 0 0 0 40 40
_umoddi3.o 0 0 0 0 40 40
xtensa_init.c.obj 0 4 32 0 0 36
interrupts--intlevel.o 0 0 0 0 32 32
esp_efuse_table.c.obj 16 0 0 0 8 24
lib_a-errno.o 0 0 0 10 0 10
pm_esp32.c.obj 0 0 0 8 0 8
int_asm--set_intclear.o 0 0 8 0 0 8
eri.c.obj 0 0 8 0 0 8
cxx_exception_stubs.cpp. 0 0 0 6 0 6
cxx_guards.cpp.obj 0 0 0 5 0 5
hello_world_main.c.obj 0 0 0 5 0 5
FreeRTOS-openocd.c.obj 4 0 0 0 0 4
dummy_main_src.c.obj 0 0 0 0 0 0
bootloader_flash.c.obj 0 0 0 0 0 0
bootloader_random.c.obj 0 0 0 0 0 0
bootloader_sha.c.obj 0 0 0 0 0 0
esp_image_format.c.obj 0 0 0 0 0 0
flash_partitions.c.obj 0 0 0 0 0 0
lib_a-fputs.o 0 0 0 0 0 0
lib_a-printf.o 0 0 0 0 0 0
lib_a-putc.o 0 0 0 0 0 0
lib_a-putchar.o 0 0 0 0 0 0
lib_a-puts.o 0 0 0 0 0 0
lib_a-sprintf.o 0 0 0 0 0 0
lib_a-strerror.o 0 0 0 0 0 0
lib_a-u_strerr.o 0 0 0 0 0 0
lib_a-xpg_strerror_r.o 0 0 0 0 0 0
gpio.c.obj 0 0 0 0 0 0
hw_random.c.obj 0 0 0 0 0 0
pm_locks.c.obj 0 0 0 0 0 0
_addsubdf3.o 0 0 0 0 0 0
_cmpdf2.o 0 0 0 0 0 0
_divdf3.o 0 0 0 0 0 0
_fixdfsi.o 0 0 0 0 0 0
_floatdidf.o 0 0 0 0 0 0
_floatsidf.o 0 0 0 0 0 0
_muldf3.o 0 0 0 0 0 0
_popcountsi2.o 0 0 0 0 0 0
platform.c.obj 0 0 0 0 0 0
platform_util.c.obj 0 0 0 0 0 0
sha256.c.obj 0 0 0 0 0 0
esp_mem.c.obj 0 0 0 0 0 0
gpio_periph.c.obj 0 0 0 0 0 0
spi_flash_rom_patch.c.ob 0 0 0 0 0 0
md5-internal.c.obj 0 0 0 0 0 0
From a library point of view, the major contributor is libc which is the C standard library. While you could probably cherry-pick some functions and drop others from there, I don't think anyone would recommend that.
Next up is libesp32, which provides critical functions such as start_cpu0(). Again, you may be able to cherry-pick only the functions you need, if you really want to.
You can figure out what a library provides by looking up the .a file (e.g. find build -name libesp32.a, and then running nm build/esp-idf/esp32/libesp32.a on the found path.
The second table lists the same size-data, but split per source-file instead of per library.