Injector Sensor Hub Firmware Design Specification

Overview

Injector Sensor Hub firmware periodically reads analog sensors and reports analog data to CAN, analog sensors include pressure transducers and hall effect sensors.

Reference Documents

TODO add documentation for OX Hall and Fuel Hall sensors?

Initialization

Setup to use external oscillator with 1xPLL
Setup PPS(Peripheral Pin Select) for CAN
Initialize ADC, setup to use FVR(Fixed Voltage Reference)
Initialize CAN module with canlib

Runtime

Heart Beat

Red LED shall toggle every 500ms.

Health Check

Health check shall be performed every 500 ms. All health check erros are signaled through GENERAL_BOARD_STATUS CAN Message.

Errors signaled by health check
Name	Condition
5V_OVER_CURRENT	I _{5V_out} > 100 mA
12V_OVER_CURRENT	I _{12V_out} > 150 mA

Sensor Reading

Firmware shall read from the following sensors:

Oxidizer Pressure Transducer
Fuel Pressure Transducer
CC Pressure Transducer
Fuel Hall Sensor
Oxidizer Hall Sensor

ADC voltage reading from PTs shall be converted to pressure using formula described in Convert pressure transducer ADC pin voltage input to pressure section. Pressure output is to be send to CAN using SENSOR_ANALOG CAN message.

TODO add blurb about how Hall Sensor reading is handled.

TODO add 4-20mA pressure transducer current check.

Refer to CAN Message Sent by Firmware section below for period of transmission and sensor IDs or refer to analog_sensor_id enum definitions.

CAN Communication

CAN Message Sent by Firmware

CAN Message Sent by Firmware
Message Type	Description	Period
GENERAL_BOARD_STATUS	Report status_ok healthcheck	500 ms
SENSOR_ANALOG.PRESSURE_OX	Report Oxidizer Pressure Transducer pressure	50 ms
SENSOR_ANALOG.PRESSURE_FUEL	Report Fuel Pressure Transducer pressure	50 ms
SENSOR_ANALOG.PRESSURE_CC	Report CC Pressure Transducer pressure	50 ms
TODO fill	Report Fuel Hall Sensor reading	250 ms
TODO fill	Report Oxidizer Hall Sensor reading	250 ms

CAN Message Handled by Firmware

CAN Message Handled by Firmware
Message Type	Description
RESET_CMD	Reset board if targeted(check with `check_board_need_reset` function in canlib)

GENERAL_BOARD_STATUS board specific error field usage

GENERAL_BOARD_STATUS board_error_bitfield Bit definition
Bitfield Name	Description	Offset
PT_OUT_OF_RANGE	4-20 mA Pressure transducer signals less that 4mA or more than 20mA	0

Mathematics Model

TODO add ADC calculations including Vref and resolution for the sensors TODO anything else that sensors are doing that I’m not aware of

Describe common used math equations in the firmware, if the equation is more than one line, then a link to a Matlab model should be provided.

Convert pressure transducer ADC pin voltage input to pressure

TODO Insert formula here