Flash Memory Guide

Estimated time to complete: 8 minutes

This guide explains the role and structure of flash memory on the OBC (On-Board Computer) board. Flash memory is used to store housekeeping (HK) and mission data from various subsystems, which can later be downlinked to the Ground Station. Communication between the OBC and these memories is handled via SPI.

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Overview of Flash Memory Usage

Flash memories are shared between the OBC and peripheral subsystems. These are non-volatile memories used for storing telemetry, payload data, configuration states, and communication-related logs.

• Communication Interface: SPI
• Memory Sector Size: 64 kB
• Main Partitions:
  • Main FM: Primary flash for core OBC operations
  • Shared Mission FM: Shared by all mission subsystems
  • Shared COM FM: Shared for communication subsystem needs

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Flash Memory Map Summary

Below is the memory allocation template. Each row describes a type of data, its address range, and the sectors it occupies:

Data Type	Address Range	Sectors	Size (kB)	Used In
SAT_Log	0x00000000 - 0x00170000	0–23	1536	Main FM, COM FM
Reset_HK	0x00190000 - 0x01850000	25–389	23360	Main FM
Address Location	0x01870000	391	64	Main FM
Address Data	0x01880000 - 0x018A0000	392–394	192	Main FM
Flag Data	0x018B0000	395	64	Main FM
RSV_Data	0x018C0000 - 0x01900000	396–400	320	Main FM
FAB_HK	0x01910000 - 0x02BC0000	401–700	19200	Main FM
FAB_CW	0x02BD0000 - 0x02EE0000	701–750	3200	Main FM
Mission STATUS	0x02EF0000 - 0x03200000	751–800	3200	Shared Mission FM
PMSN APRS Data	0x03210000 - 0x03840000	801–900	6400	Main FM, Shared COM FM
I-C Data	0x03850000 - 0x03E80000	901–1000	6400	Shared Mission FM
RMSN CAM Thumbnails	0x03E90000 - 0x041A0000	1001–1050	3200	Shared Mission FM
RMSN CAM Images	0x041B0000 - 0x044C0000	1051–1100	3200	Main FM, Shared COM FM
TUM Payload Data	0x044D0000 - 0x04B00000	1101–1200	6400	Main FM, Shared COM FM
ADCS Data	0x04B10000 - 0x05140000	1201–1300	6400	Main FM
TLE (GPS) Data	0x05150000 - 0x05460000	1301–1350	3200	Main FM, Shared COM FM

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Key Notes

• Address Location stores the starting address of data logs; this address is updated on boot and overwrites old data.
• Address Data contains structured metadata (e.g., flag and HK addresses) used by the OBC firmware.
• Flag and RSV Data are used for system state management and reserved operations.
• Mission Subsystems (like Paraguay, Moldova, and Rwanda missions) store their payload data in designated shared areas.
• ADCS & GPS store telemetry relevant to satellite orientation and positioning.

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Best Practices

• Avoid Overwriting: Some memory areas (e.g., Address Data, Flag Data) overwrite older content—ensure your firmware handles this safely.
• Mission Isolation: When allocating new memory for a mission, ensure no overlap with existing sectors.
• Clear Sector Mapping: Always update the sector map and inform team members of changes to avoid conflicts.

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Visualization

Below is an example memory map diagram :

pie title Flash Memory Allocation (by sector count)
    "SAT_Log [1536kB]" : 24
    "Reset_HK [23360kB]" : 365
    "Address Data location [64kB]" : 1
    "Address Data [192kB]" : 3
    "Flag Data [64kB]" : 1
    "RSV_Data [320kB]" : 5
    "FAB_HK [19200kB]" : 300
    "FAB_CW [3200kB]" : 50
    "Mission STATUS [3200kB]" : 50
    "PMSN APRS payload data [6400kB]" : 100
    "I-C [6400kB]" : 100
    "RMSN CAM Thumb [3200kB]" : 50
    "RMSN CAM IMG [3200kB]" : 50
    "TUM payload data [6400kB]" : 100
    "ADCS [6400kB]" : 100
    "TLE [3200kB]" : 50