This directory contains the firmware source code for the Data Acquisition (DAQ) board, responsible for data collection, storage, and streaming.

Directory Structure

• main.c / main.h - Main entry point for DAQ firmware, responsible for initialization and thread management.
• can_irq/ - CAN RX IRQ implementations, consuming CAN busses and feeding the SPMC
• spmc/ - Custom lockless Single Producer Multiple Consumer queue implementation for high throughput data buffering between CAN IRQs and consumer threads (SD card writing, Ethernet streaming).
• rtc_sync/ - Synchronization of the RTC peripheral with the reported GPS time
• sd_card/ - SD logging and file management
• ethernet/ - Real-time UDP streaming of CAN bus activity wirelessly

DAQ SPMC Queue

Specialized data structure designed specifically for DAQ.

• Lockless
• Priority aware
• High throughput
• DMA friendly

DAQ26 setup:

• Producer(s): CAN1 and CAN2 ISRs
• Master Consumer: SD thread
• Follower Consumer: Ethernet thread

Notes:

• Even though there are actually two producing ISRs (CAN1 and CAN2), they have the same priority and cannot preempt each other, so we can treat them as a single producer for the purposes of this data structure.
• Data is returned to the consumers in contiguous chunks to optimize for DMA transfers.
  • The total capacity of the buffer is sized to be a multiple of chunk size to prevent fragmentation.
• If the SD thread falls behind, data will be dropped until it catches up. These "overflows" are tracked in a counter.
  • Several buffer parameters can be tuned to reduce the likelihood of overflows.
• If the ETH thread falls far behind the SD thread, it will fast-forward its tail to the location of the SD thread. The "dropped frames" are also tracked in a counter.

Note

todo more detailed docs

sd fsm

timing diagram