Each UART port and associated subsystem behaves at least a little bit differently. This document captures these behaviours.

UART1 - MPI

• High baud rate - 230400 baud
• DMA access

UART2 - AX100

• Baud rate: 230400 baud
• Used exclusively to receive uplinks.
• AX100 sends data encoded with KISS encoding (escape/start/end special bytes).
• Interrupt-based.
• Messages can be received at any time.
• Note that, for simplicity of implementation, downlink is commanded over I2C to the AX100.

UART3 - GNSS

• Baud rate: 115200 baud
• Interrupt-based.
• Interrupt disabled by default. Very cautious about enabling it, as the GNSS is known to spam null bytes if misconfigured.

UART4 - Camera

• Variable baud rate. 115200 default, but decreased to 9600 by command right away to ease writing to LittleFS and avoid dropped data.
• DMA access
• Does not support receiving arbitrary data after transmitting arbitrary data (via the CTS1+TCMDEXEC_uart_send_hex_get_response_hex command).
  • Justification: Unnecessary complexity. Not a mission requirement. The camera doesn't really have a "command-mode" like all other UART peripherals do.

UART5 - EPS

• Baud rate: 115200 baud
• Interrupt-based.
• Interrupt enabled by default, and is trusted.
• EPS only responds to commands, and does not send messages otherwise.

LPUART1 - Debug/Umbilical

• Baud rate: 115200 baud
• Interrupt-based.
• Interrupt enabled by default, and is trusted. Always on.