[BLE] esp32 study

자전거와 esp32를 연결하여 자전거로 운동을 한다면,
얼마나 칼로리가 소모됐는 지, 몇 시간 했는지를 알기위해 사용할 device인 esp32를 공부해보았다.

device : esp32-wroom-32d
device spec : 

Schematics

Pin Map

ESP32-WROOM-32D Specifications

Strapping Pins : 

ESP32 has five strapping pins,
1.MTDI(GPIO12)
2.GPIO0
3.GPIO2
4.MTDO(GPIO15)
5.GPIO5

Software can read the values of these five bits from register “GPIO_STRAPPING”
During Chip’s system reset release( power-on reset, watchdog reset and brownout reset), hold these bit until the chip is powered down or shut down.
To change the strapping Bit values, users can apply external pull-down/pull-up resistances, or use the host MCU’s GPIO.

CPU and Internal Memory

ESP32-D0WD contains a dual-core Xtensa® 32-bit LX6 MCU
448KB of ROM : bootloader
++user program은 외부 SPI flash에 저장한다.
520KB of on-chip SRAM : data and instructions
따라서 사용자가 일반적으로 가용할 수 있는 memory size는 4MByte(SPI flash) + 520KB(Program data)가 된다.

Boot-related pins

1.EN : reset
2.GPIO0 : Select Boot mode, default Pull-up
- High : Run SPI Flash user program
- Low : Run internal Rom Serial Boot loader
ESP32는 EN핀이 LowàHigh가 될 때, GPIO0의 상태를 읽어 부팅모드 결정
3. GPIO2 : When entering Serial Boot Mode, GPIO2 must be plotting or Low
- input mode : When esp32 is boot, if GPIO2 is high, it may not enter bootloader model.
- output mode : pull-down is stable
4. GPIO12(MTDI) : default Pull-down, 3.3V
- High : Determine voltage of internal SPI Flash as 1.8V
- Low : Determine voltage of internal SPI Flash as 3.3V
5. GPIO15(MTDO) : Boot log output at boot time
-High : Outputs the booting log (default)
-Low : Do not output booting log

 SPI, UART-related pins

전공자라면, 이정도의 정보를 통해 esp32를 자유롭게 다룰 수 있을 것이다.