Figure 2.15 is a top-level block diagram showing the flow of information to and from the MIPS instrument. As shown in the Figure, operational parameters are converted into the appropriate command blocks at the ground station, which are then uplinked to Spitzer. Instrument-specific commands are received and distributed by the spacecraft command and data handler (C&DH). The C&DH provides the interface between the Spitzer spacecraft and the Spitzer instruments. The spacecraft C&DH sends the MIPS-specific commands on to the IRS/MIPS processor; there they are interpreted and executed by the Control Section Flight Software (CSFS). Engineering and science data are gathered by the various components of the MIPS embedded flight software and downlinked, via the spacecraft processor, to the ground for processing.
The CSFS configures and controls the instrument components through four major electronics sections: the Spitzer Instrument Command and Data handling (C&DH) subsystem interface, the Control Section Electronics (CSE), the Silicon Detector Focal Plane Array (Si FPA) Interface Electronics, the Germanium Detector Focal Plane Array (Ge FPA) Interface Electronics, and the Cryogenic Scan Mirror Mechanism (CSMM) Interface. Within the IRS/MIPS electronics, the CSFS provides the instruments with the computational, interface, and memory resources necessary for performing overall instrument control and science data collection and processing tasks. Commands are accepted through an RS-422 Command/Response Serial interface to the spacecraft C&DH and then processed by the CSFS. The engineering telemetry data are output by the CSFS to the spacecraft C&DH via the same interface. Instrument science data and diagnostic data are output by the CSFS to the spacecraft C&DH via the 1Mb RS-422 Science Data interface. The Si FPA Interface Electronics and the Ge FPA Interface Electronics provide the commanding and science data interface between MIPS detectors and the CSFS. The Si and Ge FPA Interface Electronics also control the instrument stimulators and the Si focal plane array temperature. The Ge FPA Interface Electronics control the MIPS cryogenic scan mirror.
Figure 2.15: MIPS software block diagram.
To perform its main function of collecting and outputting science and engineering data within the constraints of the Spitzer system, the CSFS provides the ability to operate the instrument in two separate software states: the boot state and the operate state. Within each software state, various subsets of the full set of commands and subsets of the full set of telemetry data are valid.
When power is applied to the main electronics of the MIPS instrument, the MIPS processor begins execution of the boot state flight software. The functions for the boot state software are:
· Provide the ability to upload and download data to/from the Error Detection and Correction / Electrically Eraseable Programmable Read Only Memory (EDAC/EEPROM) memory areas from/to the ground system via the spacecraft C&DH.
· Provide the ability to transfer the code from the EEPROM memory area into the EDAC RAM.
· Provide the ability to begin execution of the Operate state software at an uplinked address location.
· Provide the ability to monitor and output a subset of the full complement of engineering data indicating the current state of the instrument.
· Collect detector, memory dump, and diagnostic data telemetry.
To protect this basic upload and transfer capability, the flight software necessary to perform the boot state software functions resides in a write-protected area of radiation-hardened EEPROM. To reduce the complexity and increase the reliability of the boot state flight software, it has been written without incorporating the real-time operating system that is being utilized in the operate state flight software. The boot state flight software utilizes a basic cyclic executive to handle its operations.
After the boot state software has copied the operate state software from EEPROM to EDAC RAM, the instrument may be commanded into the operate state, where instrument science activities can be performed. All instrument calibrations, science observations and instrument diagnostic activities are performed by the operate state software. To accomplish this, the operate state software supports the following tasks:
· Configure and operate the MIPS detectors.
· Configure and operate the MIPS scan mirror.
· Configure and control the MIPS instrument stimulators.
· Collect detector, memory dump, and diagnostic data telemetry.
· Collect and monitor engineering data and scan mirror position data.
· Format and output science data to the RS-422 Serial interface.
· Format and output engineering telemetry data to the RS-422 Serial interface.
