All OpenIMU hardware modules come shipped pre-configured with a special bootloader resident in their FLASH memory. This bootloader allows for in-system code updates using a UART connection without using JTAG. Sample code that utilizes this Bootloader can be found in the OpenIMU Python driver. An example of how to invoke the Python driver for code loading is here.
The full details of the bootloader serial protocol is described below. These commands are executed using OpenIMU’s standard serial interface:
A user can initiate bootloader at any time by sending ‘JI’ command (see below command’s format) to application program. This command forces the unit to enter bootloader mode. The unit will communicate at 57.6Kbps baud rate regardless of the original baud rate the unit is configured to. The Bootloader always communicates at 57.6Kbps until the firmware upgrade is complete.
As an additional device recovery option immediately after powering up, every OpenIMU will enter a recovery window of 100ms prior to application start. During this 100mS window, the user can send ‘JI’ command at 57.6Kbs to the Bootloader in order to force the unit to remain in Bootloader mode.
Once the device enters Bootloader mode via the ‘JI’ command either during recovery window or from normal operation, a user can send a sequence of ‘WA’ commands to write a complete application image into the device’s FLASH.
After loading the entire firmware image with successive ‘WA’ commands, a ‘JA’ command is sent to instruct the unit to exit Bootloader mode and begin application execution. At this point the device will return to its original baud rate.
Optionally, the system can be rebooted by toggling the power or toggling nRst (pull low and release) to restart the system.
Firmware Update Commands
The commands detailed below are used for upgrading a new firmware version via the UART at 57.6Kbps.
Jump to Bootloader Command
Jump To Bootloader (‘JI’=0x4A49) Preamble Packet Type Length Payload Termination 0x5555 0x4A49 0x00 CRC(U2)
The command allows system to enter bootloader mode.
Write App Command
Write APP (‘WA’=0x5741) Preamble Packet Type Length Payload Termination 0x5555 0x5741 len+5 CRC(U2)
The command allows users to write binary sequentially to flash memory in bootloader mode. The total length is the sum of payload’s length and 4-byte address followed by 1-byte data length. See the following table of the payload’s format.
WA Payload Contents Byte Offset Name Format Scaling Units Description 0 staringAddr U4
bytes The FLASH word offsetto begin writing data 4 byteLength U1
bytes The word length of thethe data to write 5 dataByte0 U1
Flash data 6 dataByte1 U1
Falsh data … … 4+byteLength dataByte U1
Payload starts from 4-byte address of flash memory where the binary is located. The fifth byte is the number of bytes of dataBytess, but less than 240 bytes. User must truncate the binary to less than 240-byte blocks and fill each of blocks into payload starting from the sixth-byte. See the reference code, function write_block(), in Appendix F.
Jump to Application Command
Jump To Application (‘JA”=0x4A41) Preamble Packet Type Length Payload Termination 0x5555 0x4A41 0x00 CRC(U2)
The command allows system directly to enter application mode.