File System

SPIFFS

• Compatible with internal SPI Flash and external SPI Flash
• No 'directories', flat filesystem
• maxchars 32
• blocksize 256
• We shall use custom write-back caching to reduce flash write cycles
• Since the requirement is to note down peers which are in contact for > 30 min
• TempIDs rotate every 15 min, we should note down peers TempIDs seen for >= 5 mins to allow for backend correlation

Cleanup

• Conditions
• /p/[mmdd] is older than 21 days
• Free space is < 20KB
• Process
• Delete /p/[mmdd]* which are >= 21 days, or oldest

Files

/ids

• List of all local Temp IDs
• Looked up to obtain Nth TempID on-demand
  

/p/[mmdd]

• map of peers TempID to
• a 5-digit running id 0-65535
• org : string
• deviceType
  

/p/[mmdd]/[id]

• Incident List
• Start Timestamp hhMMss : 3 bytes
• Seen Minutes : 1 byte
• RSSI min, max, mean, var/stddev : 4 bytes

Future Optimization

• In locations where certain TempIDs are permanently close to each other
• Define a metric to decide on such devices
• Note down these TempIDs to put them in an ignore / always-together list