What does CDHS do?
CDHS aka Command and Data Handling System is basically an on-board computer that controls the operation of the satellite during normal conditions. In CDHS, mission and housekeeping data from all subsystems is stored and prepared for downlink via COM. CDHS also runs the processes of the Attitude Determination and Control System (ADCS).
Inside CDHS
The system contains two STM32F103 ARM processors, one of which is turned on at a time. Two cold redundant processors allow for the satellite to remain operational in case of a processor failure. External memory devices are shared between the processors.
On board CDHS, there are 3 SPI Flash memories (Spansion S25FL128P), 16 MB each. Flash memories are used for storing large amounts of mission and housekeeping data as well as camera photos. In addition, there are 5 SPI FRAM devices (Ramtron FM25V20), 256 KB each. FRAM is used for storing file system metadata, system files and CDHS firmware images.
| No. | Device | Feature | Value |
|---|---|---|---|
| 2 | STM32F103VFT | Flash | 768 KB |
| SRAM | 96 KB | ||
| Clock | .. 72 MHz | ||
| 5 | FM25V20 | SPI FRAM | 256 KB (1280 KB in total) |
| SPI Clock | .. 20 MHz | ||
| 3 | S25FL128P | SPI Flash | 16 MB (48 MB in total) |
| SPI Clock | .. 20 MHz | ||
| 1 | DS3234 | SPI RTC |