Bootloader design - hardware

Bootloader design - software

Program flow

Bootloader detection

• sensor_pullup_cmd pin is set low
• delay
• if sensor_sig voltage > 0.9*Vcc - enter bootloader

Supported commands

Command codes are selected to be hard to be mistaken if software UART reading is started in the middle of bit.

• Erase (0x81)
  • Application flash, not bootloader
• Write data (0x82)
  • In 128B chunks
  • CRC32
• Get information (0x84)
  • 1024B block with CRC
  • Bootloader version
  • Application version (info block in application flash)
  • Chip ID
  • Other bytes reserved (logs?)
• Run application (0x88)

Bootloader tests

Communication tests

Transmission from device via high side driver

Test is done using circuit below: First test with no serial and parallel resistors. Falling edge is slow and transistor turn off threshold voltage is too high.

• CH1: HEATER
• CH2: OUT Second test with Serial 220k and parallel 2k2 resistors.
• CH1: HEATER
• CH2: OUT
• CH3: IN Rise and fall time are ~100us and ~150us. But according to datasheet, they can be as high as 500us.

Reception from USB-UART

Test is done using circuit below: