Blue Pill notes (STM32F103C8T6)


#undef LED_BUILTIN
#define LED_BUILTIN PC13

$ st-info --probe
...
Found 1 stlink programmers
  version:    V2J29S7
  serial:     51FF69064975525012352367
  flash:      20971520 (pagesize: 1024)
  sram:       20480
  chipid:     0x0410
...

find /tmp/arduino* -type f  | grep bin$

st-flash --reset write /tmp/arduino_build_950069/Blink.ino.bin 0x08000000

Blink Pi (with no dot)

// BLINK PI

#undef LED_BUILTIN
#define LED_BUILTIN PC13

const char Pi[] = "31415926536";  // with no "."

void send(int n) {
  delay(500);
  for (int i = 0; i < n; i++) {
    delay(200);
    digitalWrite(LED_BUILTIN, LOW);    // ON
    delay(200);
    digitalWrite(LED_BUILTIN, HIGH);   // OFF
    delay(200);
  }
  delay(500);
}

// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);
  digitalWrite(LED_BUILTIN, HIGH);   // OFF
}

// the loop function runs over and over again forever
void loop() {
  for (int p = 0; Pi[p]; p++) {
    send(Pi[p] - '0');
  }
  delay(3000);
}

This does a square wave on PC13 with 1.37 microsecond period (optimized for space) or 1.47 microseconds (for speed, -O3):

// BLINK FAST, HOW FAST?

//#undef LED_BUILTIN
//#define LED_BUILTIN PC13

void BlinkFast(unsigned n) {
  for (unsigned i = 0; i < n; i++) {
    digitalWrite(LED_BUILTIN, LOW);    // ON
    digitalWrite(LED_BUILTIN, HIGH);   // OFF
  }
}

// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);
  digitalWrite(LED_BUILTIN, HIGH);   // OFF
}

// the loop function runs over and over again forever
void loop() {
  BlinkFast(0xFFFFFFFFu);
}

.arduino15/packages/stm32duino/hardware/STM32F1/2021.5.31/system/libmaple/include/libmaple/gpio.h

/**
 * Set or reset a GPIO pin.
 *
 * Pin must have previously been configured to output mode.
 *
 * @param dev GPIO device whose pin to set.
 * @param pin Pin on to set or reset
 * @param val If true, set the pin.  If false, reset the pin.
 */
static inline void gpio_write_bit(gpio_dev *dev, uint8 pin, uint8 val) {
    val = !val;          /* "set" bits are lower than "reset" bits  */
    dev->regs->BSRR = (1U << pin) << (16 * val);
}

/**
 * Determine whether or not a GPIO pin is set.
 *
 * Pin must have previously been configured to input mode.
 *
 * @param dev GPIO device whose pin to test.
 * @param pin Pin on dev to test.
 * @return True if the pin is set, false otherwise.
 */
static inline uint32 gpio_read_bit(gpio_dev *dev, uint8 pin) {
    return dev->regs->IDR & (1U << pin);
}

.arduino15/packages/stm32duino/hardware/STM32F1/2021.5.31/cores/maple/wirish_digital.cpp

#include "wirish_time.h"
#include "boards.h"

uint32 digitalRead(uint8 pin) {
    if (pin >= BOARD_NR_GPIO_PINS) {
        return 0;
    }

    return gpio_read_bit(PIN_MAP[pin].gpio_device, PIN_MAP[pin].gpio_bit) ?
        HIGH : LOW;
}

void digitalWrite(uint8 pin, uint8 val) {
    if (pin >= BOARD_NR_GPIO_PINS) {
        return;
    }

    gpio_write_bit(PIN_MAP[pin].gpio_device, PIN_MAP[pin].gpio_bit, val);
}

this did not blink?

// BLINK FAST, HOW FAST?

#include "wirish_time.h"
#include "boards.h"

void BlinkFaster(unsigned n) {
  gpio_dev *dev = PIN_MAP[LED_BUILTIN].gpio_device;
  auto* regs = dev->regs;
  uint8 bit = PIN_MAP[LED_BUILTIN].gpio_bit;
  uint8 on = (1U << bit) << (16 * false);
  uint8 off = (1U << bit) << (16 * true);
  volatile uint32* pointer = &regs->BSRR;
  for (unsigned i = 0; i < n; i++) {
    // regs->BSRR = on;
    // regs->BSRR = off;
    *pointer = on;
    *pointer = off;
  }
}

void BlinkFast(unsigned n) {
  for (unsigned i = 0; i < n; i++) {
    digitalWrite(LED_BUILTIN, LOW);    // ON
    digitalWrite(LED_BUILTIN, HIGH);   // OFF
  }
}

// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);
  digitalWrite(LED_BUILTIN, HIGH);   // OFF
}

// the loop function runs over and over again forever
void loop() {
  BlinkFaster(0xFFFFFFFFu);
}