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45 lines
1.8 KiB
45 lines
1.8 KiB
7 years ago
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# GEX's internal structure
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GEX is modular, composed of functional blocks called *units*. A unit can be e.g. SPI or a digital output.
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There can be more than one instance of a given unit, based on the microcontroller's hardware resources.
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Some units use hardware peripherals, others are implemented in software. Those "soft" units (typically
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bit-banged protocols) are limited only by the available GPIO pins.
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## Resources
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A system of resource claiming is implemented to avoid units conflicting with each other and interfering with
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peripherals used internally by the system (such as the LED pin). Each unit claims the resources it uses during
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initialization. If the resource needed is not available, it may try to claim an alternate resource or fail to
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initialize.
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A init failure is reported in the config file as an error message under the unit's header.
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An example of defined resources:
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- all GPIO pins
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- timers/counters
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- SPI, I2C, USART peripherals
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- DMA channels
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## Unit identification
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Each unit has a *name* and a *callsign* (1-255) used for message addressing. Both are defined in the config file.
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There can be up to 255 units, in practice fewer due to storage limitations.
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## Unit commands and events
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Units can receive command messages (`UNIT_REQUEST`) and report asynchronous events using `UNIT_REPORT` frames.
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A command is identified by a number 0-127. The highest bit (0x80) of the command number is reserved to request
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confirmation (a `SUCCESS` frame) if the command doesn't normally generate a response. This is used by the client
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library to check that an operation was completed correctly (as opposed to e.g. the firmware crashing and rebooting
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through the watchdog).
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Unit events include the unit's callsign, a number 0-255 identifying the event type, and a 64-bit microsecond
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timestamp.
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See [FRAME_FORMAT.md](FRAME_FORMAT.md) for the payloads structure.
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