Design main engine workflow

[cristoferz]

The workflow has to be able to handle the following features:

• Arduino ports configuration (Input, Output, Analogic, PWM). May be necessary to reserve some ports according to arduino features
• Store the ladder logic for the engine
• Configuration and logic has to be stored on EEPROM
• Be possible to store some variables on EEPROM to preserve current states
• Be possible to monitor ports and variables states via USB interface as well to set variables
• Have a unique identifier (maybe UUID) for each arduino

[cristoferz]

Initial drawing for the EEPROM memory structure for storing the configuration:

|DEVICE-UUID|VERSION-UUID|VARIABLES|CONFIGURATION|PROGRAM|

These memory areas is detailed as following:

• DEVICE-UUID: Uniquely identifies the device. Has to be generated on first usage of device. Size: 16 bytes
• VERSION-UUID: Uniquely identify the loaded version of program to the arduino. On each load is recommended to be generated a new one. Size: 16 bytes
• VARIABLES: Stores variables to preserve states across possible device reboots. Is recommend to be cleared whenever a new program version is loaded to device to avoid inconsistent reads. The size can be defined to better suit the available EEPROM for each device.
• CONFIGURATION: General setup configurations necessary for the device. At this point stores only port configurations. The size can vary according to used board, since there are different number of ports or features.
• PROGRAM: Stores the engine logic to be executed by the engine. The size can vary according to available EEPROM on each device.

[cristoferz]

Once started, the arduino can load the program to memory and start running it in cycles, applying the logics for each lane. In case of program reload, the memory have to also be reloaded.

[cristoferz]

As ladder logic is mostly based on flows, the result of an operation can be passed to the next one, until the end of the lane. Some operation does not use this previous state, so can be ignored. If some operations do not change states, so they can just pass the previous state forward.

[cristoferz]

Port configuration can be of types:

• Input: 0x00
• Output: 0x01
• Output (PWM): 0x02

As supported by Arduino. Analogic ports can use the same values except for PWM. As configuration will have 1-byte, the remaining values can be reserved for future features (e.g. I2C communications)