1. 4/27/20018644-T7C - DCM Software Interface ISUAL DPU-to-DCM Interface and Protocol 8644-T7C Rev Description Date A Initial release 20-Feb-2001 SG B MMCB Format changes, List in MM 12-Apr-2001 SG C Cleanup, add flowcharts 27-Apr-2001 SG

2. 4/27/20018644-T7C - DCM Software Interface DCM Program DCM starts with a ROM program. DPU copies the compression software into Mass Memory (MM). This is called the Program Logic Block (PLB) DPU sends CDI commands to tell DCM where the PLB is located.

3. 4/27/20018644-T7C - DCM Software Interface CDI Commands for setting PLB address CDI commands to set the address of the PLB area: –operation=36 hex data=high 2 bytes of address –operation=37 hex data=low 2 bytes of address

4. 4/27/20018644-T7C - DCM Software Interface Layout of PLB Area 4 bytes - number of bytes (N) in DSP program 1 byte - checksum of DSP program (covering N bytes) N bytes - the DSP program (up to 256K bytes) Number of bytes is stored high-byte-first (example: decimal 123456 is stored hex 00 01 E2 40) This convention is used for all number storage. The PLB checksum is the exclusive-OR of all N bytes in the DSP program.

5. 4/27/20018644-T7C - DCM Software Interface How the DCM gets data to compress There is a list of 16 Mass Memory Control Blocks (MMCB), written in to MM by the DPU. MMCBs specify where the data is within MM. DCM does up to 16 compression “jobs” at a time, one for each MMCB

6. 4/27/20018644-T7C - DCM Software Interface MMCB Compression List The list of 16 MMCB copies in MM is called the “Compression List” The address of the first MMCB in the list is set by CDI commands.

7. 4/27/20018644-T7C - DCM Software Interface CDI Commands for Setting MMCB address CDI commands to set the address of the initial MMCB: –operation=34 hex data=high 2 bytes of address –operation=35 hex data=low 2 bytes of address

8. 4/27/20018644-T7C - DCM Software Interface How the DCM uses the Compression List The DCM software processes each MMCB in the list. –If the checksum fails, DCM goes to the next MMCB –Otherwise, DCM compresses the data, marks the MMCB complete and goes to the next one. –After processing the last MMCB, the DCM deactivates Busy, and waits for an ATN signal.

9. 4/27/20018644-T7C - DCM Software Interface

10. 4/27/20018644-T7C - DCM Software Interface Normal Processing

11. 4/27/20018644-T7C - DCM Software Interface MMCB Layout [offset 0, 1 byte] Status: – 0=no operation required – 1=readout complete, ready to compress – 2=compression complete [offset 1, 1 byte] Input Data type: – 0=Camera - Aurora – 1=Spectrophotometer – 2=Slow-Rate Spectrophotometer – 3=Array Photometer

12. 4/27/20018644-T7C - DCM Software Interface MMCB Layout [offset 2, 1 byte] mmcb_mode - Science Mode –1=Aurora –2=Sprite Continuous –3=Sprite Burst [offset 3, 4 bytes] mmcb_OI –Pointer to Original Input raw data in MM [offset 7, 4 bytes] mmcb_OI_n –Number of OI bytes allocated

13. 4/27/20018644-T7C - DCM Software Interface MMCB Layout [offset 11, 6 bytes] (not used by DCM) [offset 17, 6 bytes] (not used by DCM) [offset 23, 2 bytes] mmcb_ns – Number of images or samples [offset 25, 1 byte] mmcb_E3 –DCM ‘E3’ status byte

14. 4/27/20018644-T7C - DCM Software Interface MMCB Layout [offset 26, 4 bytes] mmcb_obytes –number of compressed bytes stored by the DCM [offset 30, 1 byte] mmcb_ochk –checksum of compressed output (XOR of all bytes)

15. 4/27/20018644-T7C - DCM Software Interface MMCB Layout [offset 31, 3 bytes] (not used by DCM) [offset 34, 1 byte] (not used by DCM) [offset 35, 1 byte] mmcb_checksum –Checksum of MMCB (XOR of previous 35 bytes)

16. 4/27/20018644-T7C - DCM Software Interface Notes Compressed Data will over-write the original information. DCM will compute a checksum of the compressed data, and a separate checksum of the updated MMCB First byte(s) of compressed data will tell the ground-based decompression software which algorithm to use

17. 4/27/20018644-T7C - DCM Software Interface Camera Data Camera data will be an array of images. –Number of columns = 512 –Number of rows = 128 Number of images: –1 or more in Aurora mode –8 in Burst mode –typically 6 in Continuous mode

18. 4/27/20018644-T7C - DCM Software Interface Photometer Data In Sprite modes, data is delivered as arrays of samples. –Size of array given in MMCB

19. 4/27/20018644-T7C - DCM Software Interface Ground Processing of Compressed Data The arrays of compressed data delivered by the DCM will be re-constituted on the ground, from the CCSDS packets. To un-compress this data, software is needed on the ground.

20. 4/27/20018644-T7C - DCM Software Interface Ground De-compression Software C functions which convert compressed arrays to the original uncompressed data. Suggestion for Camera function: uncmp_cam(byte *pci, int nci, byte *poi) –pci points to compressed array –nci is now many bytes in compressed array –poi is where to store the uncompressed data

21. 4/27/20018644-T7C - DCM Software Interface Photometer Functions Similarly: uncmp_sph(byte *pci, int nci, byte *poi)

22. 4/27/20018644-T7C - DCM Software Interface END