Improve flash usage with STM32F030F4P6

[evil-gears]

Hello, would like to request a "flash usage improvement" (not really sure what to call it) for STM32F030F4P6.

The issue is that this MCU is already limited in terms of flash size when compared to others of the F030 line by having only 16KB, however the main problem is that in core 2.10.1@Arduino IDE 2.3.4, even using the "smallest with LTO" compiler optimization, a completely empty sketch consumes around 8576 bytes (52%) of the flash and 1328 bytes (32%) of the SRAM, which effectively limits the program size to around 8KB, which is easily taken up completely by a simple sketch if a library or a timer is included.

If I disable U(S)ART support (even though it's not even called/initialized) it gets a bit better at 2708 bytes (16%) of program storage space, so I suspect it has to do with all the HAL libraries it has to load up.

Meanwhile, an AVR board of the same flash size compiles an empty sketch at no more than 1% of the program storage space. I know the architectures are very different, but I think that a 32-bit MCU should be better flash-wise than an 8-bit one, not worse...

In my case, I have a code that runs on HSI, uses TIM3 as an interrupt callback for timing and has a state-machine composed of a half-dozen cases inside a switch-case funtion that toggles 6 outputs based on 2 inputs. This rather simple code takes up 12884 bytes (78%) of the program storage space with LTO and a whooping 15392 bytes (93%) without LTO. These numbers go down to a much nicer 7616 bytes (46%) with LTO and 11612 bytes (70%) without LTO if I disable U(S)ART, and in this case I'm not using it anyway.

However, I still think it's rather absurd the core has to take up so much flash to do these simple tasks. Is there something that could be improved on the next release to fix this? Thanks in advance.

[fpistm]

Hi @evil-gears
I know the core use lot of flash for basic sketch and is not compatible by default with small device.
Core is generic and so thi increase the size compared to a bare code. That's why compared it to a core designed for a dedicated board is not relevant compare to a core supporting more than 1k boards.

You can try to:

• disable unneeded HAL module:
  https://github.com/stm32duino/Arduino_Core_STM32/wiki/HAL-configuration#example-of-blinkino-for-nucleo-l031k6-with-32768-bytes-of-flash-and-8192-bytes-of-ram
• redefine the system clock config to use only LL API.
• redefine pinmap array if you used pin from it, specifically TIM if you use it, if you disable some HAL module some of them will be disabled by default: https://github.com/stm32duino/Arduino_Core_STM32/wiki/Custom-definitions#custom-pinmap-array

[fpistm]

Here result with different step for a Nucleo F042K6 with this example:

Serial enabled (Default config)

Sketch uses 24852 bytes (75%) of program storage space. Maximum is 32768 bytes.
Global variables use 1384 bytes (22%) of dynamic memory, leaving 4760 bytes for local variables. Maximum is 6144 bytes.

Serial disabled:

Sketch uses 17232 bytes (52%) of program storage space. Maximum is 32768 bytes.
Global variables use 844 bytes (13%) of dynamic memory, leaving 5300 bytes for local variables. Maximum is 6144 bytes.

Serial disabled + build_opt.h

Sketch uses 16508 bytes (50%) of program storage space. Maximum is 32768 bytes.
Global variables use 524 bytes (8%) of dynamic memory, leaving 5620 bytes for local variables. Maximum is 6144 bytes.

Serial disabled + build_opt.h + PinMap_TIM redefined

Sketch uses 16184 bytes (49%) of program storage space. Maximum is 32768 bytes.
Global variables use 524 bytes (8%) of dynamic memory, leaving 5620 bytes for local variables. Maximum is 6144 bytes.

Serial disabled + build_opt.h + PinMap_TIM redefined + LL clock config

Sketch uses 13944 bytes (42%) of program storage space. Maximum is 32768 bytes.
Global variables use 524 bytes (8%) of dynamic memory, leaving 5620 bytes for local variables. Maximum is 6144 bytes.

No change if LTO enabled. After all this step hard to reduce main excet if you implement yourself the timer management done by the HardwareTimer library.

build_opt.h content:

-DHAL_ADC_MODULE_DISABLED
-DHAL_I2C_MODULE_DISABLED
-DHAL_RTC_MODULE_DISABLED
-DHAL_SPI_MODULE_DISABLED
-DHAL_DAC_MODULE_DISABLED
-DHAL_EXTI_MODULE_DISABLED
-DHAL_ETH_MODULE_DISABLED
-DHAL_SD_MODULE_DISABLED
-DHAL_QSPI_MODULE_DISABLED

PinMap_TIM redefined as:

const PinMap PinMap_TIM[] = {
  {PB_3,      TIM2,  STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM2, 2, 0)}, // TIM2_CH2
  {NC,        NP,    0}
};

SystemClock_Config using LL:

void SystemClock_Config(void) {
  LL_FLASH_SetLatency(LL_FLASH_LATENCY_1);
  while (LL_FLASH_GetLatency() != LL_FLASH_LATENCY_1) {
  }
  LL_RCC_HSI48_Enable();

  /* Wait till HSI48 is ready */
  while (LL_RCC_HSI48_IsReady() != 1) {
  }
  LL_RCC_SetAHBPrescaler(LL_RCC_SYSCLK_DIV_1);
  LL_RCC_SetAPB1Prescaler(LL_RCC_APB1_DIV_1);
  LL_RCC_SetSysClkSource(LL_RCC_SYS_CLKSOURCE_HSI48);

  /* Wait till System clock is ready */
  while (LL_RCC_GetSysClkSource() != LL_RCC_SYS_CLKSOURCE_STATUS_HSI48) {
  }
  LL_Init1msTick(48000000);
  LL_SetSystemCoreClock(48000000);
}

Final sketch, build_opt.h have to be created with above content:

/*
  All-in-one setPWM
  This example shows how to configure a PWM with HardwareTimer in one single function call.
  PWM is generated on `LED_BUILTIN` if available.
  No interruption callback used: PWM is generated by hardware.
  Once configured, there is no CPU load.
*/

/*
  Note: Please verify that 'pin' used for PWM has HardwareTimer capability for your board
  This is specially true for F1 serie (BluePill, ...)
*/
#include "stm32yyxx_ll_rcc.h"
#include "stm32yyxx_ll_system.h"
#include "stm32yyxx_ll_utils.h"

#if defined(LED_BUILTIN)
#define pin LED_BUILTIN
#else
#define pin D2
#endif

const PinMap PinMap_TIM[] = {
  { PB_3, TIM2, STM_PIN_DATA_EXT(STM_MODE_AF_PP, GPIO_PULLUP, GPIO_AF2_TIM2, 2, 0) },  // TIM2_CH2
  { NC, NP, 0 }
};

void SystemClock_Config(void) {
  LL_FLASH_SetLatency(LL_FLASH_LATENCY_1);
  while (LL_FLASH_GetLatency() != LL_FLASH_LATENCY_1) {
  }
  LL_RCC_HSI48_Enable();

  /* Wait till HSI48 is ready */
  while (LL_RCC_HSI48_IsReady() != 1) {
  }
  LL_RCC_SetAHBPrescaler(LL_RCC_SYSCLK_DIV_1);
  LL_RCC_SetAPB1Prescaler(LL_RCC_APB1_DIV_1);
  LL_RCC_SetSysClkSource(LL_RCC_SYS_CLKSOURCE_HSI48);

  /* Wait till System clock is ready */
  while (LL_RCC_GetSysClkSource() != LL_RCC_SYS_CLKSOURCE_STATUS_HSI48) {
  }
  LL_Init1msTick(48000000);
  LL_SetSystemCoreClock(48000000);
}

void setup() {
  // no need to configure pin, it will be done by HardwareTimer configuration
  // pinMode(pin, OUTPUT);

  // Automatically retrieve TIM instance and channel associated to pin
  // This is used to be compatible with all STM32 series automatically.
  TIM_TypeDef *Instance = (TIM_TypeDef *)pinmap_peripheral(digitalPinToPinName(pin), PinMap_PWM);
  uint32_t channel = STM_PIN_CHANNEL(pinmap_function(digitalPinToPinName(pin), PinMap_PWM));


  // Instantiate HardwareTimer object. Thanks to 'new' instantiation, HardwareTimer is not destructed when setup() function is finished.
  HardwareTimer *MyTim = new HardwareTimer(Instance);

  // Configure and start PWM
  // MyTim->setPWM(channel, pin, 5, 10, NULL, NULL); // No callback required, we can simplify the function call
  MyTim->setPWM(channel, pin, 5, 10);  // 5 Hertz, 10% dutycycle
}


void loop() {
  /* Nothing to do all is done by hardware. Even no interrupt required. */
}