IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 40, NO. 4, AUGUST 1993 91 3

A Remote Console System for Balloon Borne Experiments

Imori M., Yoshimura K., Ueda I., Yoshida T., Anraku K., Inaba S.*, Saeki T., Honda H., Matsunaga H., Motoki M.**, Nozaki M.**, Takimi N.**, Yamagami T.***

Faculty of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo 113 Japan National Laboratory for High Energy Physics(KEK)*, Oho 1-1, Tsukuba-si, Ibaraki-ken 305 Japan

Faculty of Science, Kobe University**, Rokko-dai 1-1, Nada-ku, Kobe-si 657 Japan Institute of Space and A s t r ~ ~ u t i ~ a l Science(lSAS)***,Yosinodai 3- 1-1, Sagamihara-si, Kanagawa-ken 229 Japan

AEMXACT

A remote console system is developed to improve remote control over experimental apparatus borne on the balloon. The remote console system, residing at a ground station for balloon borne experiments, sends commands to the apparatus and receives transmissions from it. The system communicates by radio with microcomputers incorporated in the experimental apparatus borne on a balloon, where the microcomputers control the apparatus individually. The system includes plural personal computers and work stations which share the transmissions from the apparatus. The transmissions from the apparatus are formatted in a bit oriented protocol, which dispenses with a fonnatter and facilitate interface with the personal computers. The article describes the implementation of the system and the communication between the ground station and the balloon-borne apparatus.

OVERVIEW

The experimental apparatus borne on a balloon is kept under the control of a ground station all the while the balloon is flown in the sky. The apparatus is linked by radio with the ground station. A remote console system is developed to improve remote control over experimental apparatus borne on the balloon. The system resides in the ground station. The system establishes remote control through communication with microcomputers incorporated in the balloon borne apparatus. The microcomputers are installed to keep individual parts of the apparatus under their control. The remote console of the microcomputers are realized in the system. A personal computer emulates a keyboard of the console and another works as its screen. The apparatus are thereby remotely controlled through the personal computers placed at the ground station. The system includes plural personal computersl(PC's) which are interconnected so as to share transmissions from the apparatus. Furthermore, one of them is incorporated into a local area network through which transactions are supplied to work stations (WS's). The transactions are processed and analyzed further in the WS's . A schematic view of the system is shown in Figure 1.

1 ~ ~ 9 8 0 1 : a product of NEC corp.

The remote console system sends command to the balloon- borne apparatus and receives transmissions from it. The apparatus is remotely controlled by commands which are typed into the emulated console keyboard. The commands are addressed to one of the microcomputers incorporated in the apparatus. The command includes the code field which specifies the microcomputer. The commands transmitted from the ground station are received by the apparatus and guided to the addressed microcomputers. Then the microcomputer processes the command. The microcomputer issues messages when the execution of the command is completed or when the microcomputer requests a command.

Storage devices of a large capacity are incorporated in the balloon-bome apparatus so that event data, the gathering of which is the object of our balloon-borne experiment, could be stored in the storage devices. So transmissions from the apparatus are limited to the messages and binary data for a monitor purpose. The transmissions received by the ground station are supplied to the remote console system. The messages are displayed by the PC which emulates the screen of the remote console. Event data and the status of the apparatus transmitted for a monitor purpose are binary formatted. The system includes PC's which are dedicated to emulate remote output devices individually. The event data and the status are displayed on the screens so that we could easily monitor the data gathering and the status.

COMMANDING

Communications with the balloon borne apparatus is based on commanding and telemetry of NSBF( National Scientific Balloon Facilities). The commanding is utilized to turn on and off switches installed in the apparatus and to send instructions to the balloon borne microcomputers where the instructions are composed of character sequences.

Discrete and Dataword Commands

An unit of radio transmission for commanding is 2 bytes wide, the one byte of which is a control field to a command receiver. The other byte is a data field and could be used for data transfer. The control field is to specify the command receiver how to process the data field. Namely, on receiving

0018-9499/93$03.00 0 1993 IEEE

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Balloon

Work Station Work Station PCs emulating remote scree

Io] - -

PC emulating Command Ground Station a remote keyboard management

computer

Figure 1: Schematic View of Remote Console System

the unit transmission, the command receiver processes the data fields specified by the control field.

When bits in the control field are set for a dataword, then the data in the data field appear on a data bus of the command receiver synchronized with the strobe pulse to sample the data bus. When the bits are set for a discrete command, the data in the data field are fed to a 8 bit decoder to activate the corresponding output of the decoder. The control field realizes continuation of the commanding over plural unit transmissions. Two byte data in successive unit transmissions are unified at the command receiver into the 16 bit data which appears on the data bus.

Command Management and Keyboard Computers

There is a command management computer which control the commanding from the ground station. A PC (hereafter called a keyboard computer) is connected to the management computer through a pair of RS232 cables. The keyboard computer communicates the management computer through an asynchronous serial link protocol where a frame is 8 bits long with a start and a stop bits and without a parity bit. The speed is 1200 bits per second.

The keyboard computer issues a request for the commanding. The format of the request differs among the dataword and the discrete commands. A dataword request includes 16 bit wide field for data. A request for a discrete command contains 8 bit field specifying the discrete command. Receiving the request, the command management computer processes the request and sends the command. The management computer acknowledges the keyboard computer after the commanding completes, returning the results of whether the Commanding is successful.

The discrete commands are used to turn on and off a variety of switches installed in the apparatus. For example, power

supplies to experimental detectors are controlled by the discrete commands. To transmit character sequences to the balloon borne computers, the dataword requests are sequentially fed to the command management computer. One dataword request is used for one byte to be transmitted. A character sequence typed into the keyboard and terminated by a carriage-return is read by the keyboard computer and converted into the byte sequence where an arbitrary number of ASCII character codes are followed by a parity byte and a null byte which is to terminate the byte sequence. Then, for each byte of the sequence, the dataword request is issued to the management computer.

Batch of Instructions

When data gathering is to be started, it is necessary to make ready experimental apparatus, to standby storage devices, to configure trigger scheme and to start the data gathering, which amounts to a lot of instructions. The same batch of instructions are required to start the data gathering. While the data gathering is running, it is also necessary to transmit, at a fmed time interval, same batch of instructions which enables us to know current status of the data gathering in details. There are many similar routine batches of instructions, for example, to turn on and off power supplies to detectors. The programs have been prepared which generate the routine batches automatically. The programs run in the keyboard computer are mostly coded in BASIC language. BASIC supports accesses to a RS232 port and manipulation of character strings. The programs run fast enough to communicate with the management computer.

TELEMETRY

Bit Oriented Protocol

Bit oriented protocol structures realize transparent data transmission from the balloon-borne apparatus. The data are

I . .

915

FLAG 1 byte

formatted according to the packet switching protocol defined in X.25 recommendation of the CCIT. The packeted data are transmitted serially in a frame format, and the data transparency is attained by zero insertion and deletion. All the frames start with an opening flag and end with a closing flag as shown in Figure 2. A frame contains the data and the frame check sequence(FCS) between these two flags. The flag is a unique pattern of 8 bits (01111110) and defines the frame boundary. The zero insertion and deletion guarantees the uniqueness of the flag sequence. A transmitter checks the transmission on a bit-by-bit basis and inserts a '0 after every sequence of five contiguous '1's lest the flag sequence should be simulated. A receiver examines the incoming frame content similarly and discards any '0' directly following the five contiguous '1's. The flags are used only to identify and synchronize the received frame. A receiver searches the incoming packets for flags on a bit-by-bit basis to establish frame synchronization.

~~

DATAFIELD FCS IFLAG Nbytes(NZ2) 2bytes I 1 byte -

Boundary buffer Frame buffer .

Receiver board

Figure 3: Relation Between Frame and Boundary Buffers

Frame Reproduction at Ground Sation

The above protocol controller is installed in the balloon- borne apparatus and works as a transmitter. A serial stream of frames from the controller is phase-modulated and fed to a radio transmitter for telemetry. Radio waves transmitted from the apparatus are received at the ground station and then submitted to the reproducing of the serial stream which was fed to the radio transmitter. The reproduced serial stream is

supplied to a bit synchronizer for demodulation. The bit synchronizer generates clocks synchronized with the frames. A simple receiver board is implemented where the protocol controller operates as a receiver. The receiver boards are installed in the individual Pc's. The serial streams of frames and the clocks are supplied to the PC's through the boards.

Frame Buffer

The receiver board interfaces the protocol controller with bus lines of the PC. The controller includes a byte-wide fifo to which data in a frame are stored temporally. The receiver board issues direct memory access @MA) requests when the fifo is not empty. While the DMA requests are present, a DMA controller operates and transfer the data in the fifo to a frame buffer allocated in the memory of the PC. The DMA controller contains a segment register and a 16 bit address counter by which an effective address of the transfer is generated. The address counter eventually points to the location in the buffer to which byte data are to be moved. The address counter is incremented everytime the DMA controller performs a byte move. Sixty-four Kbytes are allotted to the frame buffer so as to cover the range of the address counter.

The receiver board generates an interrupt when all the data in the frame have been moved to the frame buffer. Activated by the interrupt from the receiver board, a receiver handler reads the address counter and retrieves a kame boundary in the frame buffer. The handler also accesses the status register of the protocol controller and read receiver status for the current frame. A boundary buffer (B buffer) is a ring buffer with a write and a read pointers. A location in the B buffer holds frame pointers (F pointers), pointing to the frame boundary in the frame buffer, and the receiver status of the associated frame as shown in Figure 3. The receiver handler stores the boundary and the status of the current frame to the location which is pointed to by the write pointer, then modifying the write pointer to point to the next location. The read pointer, pointing to a location in B buffer, are kept under the control of a frame distributor. The read pointer is incremented when the frame pointed to by the F pointer in the location is processed by the frame distributor.

Frame Distributor

A kernel residing on the PC realizes a real-time multi-task environment. Tasks and handlers are kept under the control of the kernel. The tasks are scheduled on a event-dnven basis. The kernel supports a variety of system calls to facilitate communication and synchronization among the tasks. Event flags and queues are available in the environment. Application programs are tasks under the kernel.

The frame distributor is an application program. The frame distributor is the only task which increments the read pointer of the B buffer. The distributor is activated by the receiver handler. The event flag, which is asserted by the receiver

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handler, eventually starts the distributor. The distributor gets frame boundaries from the locations pointed to by the read pointer , modifying the read pointer incrementally. Then the distributor reads the fiist few byte of the frame to get the address of the frame, and the frame boundaries are distributed to the tasks for further process. The distributor is deactivated when the read and the write pointers come to point to the same location in the B buffer.

Network Communication and Router

Network communication is realized by system calls implemented by a network service (NS) controller. The NS controller is installed and brought under the control of the kernel where the network communication is utilized. The NS controller is a package of the handler and the tasks which cooperate to serve application programs. The handler processes interrupts from a network access board. The board interfaces the PC with communication media of the network. A processor is mounted on the board. The Intemet virtual circuit transport layer protocol is implemented on the processor. The protocol is autonomously processed by the processor, which reduces disturbances to the Pc. The NS controller supports network services at a socket layer. A socket is a bidirectional endpoint of communication. In the layer, a reliable virtual circuit transport layer is embodied in multiple paired connections of the sockets. A open system call is used to open a connection for communication. A close system call closes the opened connection. Once a connection is open, communication through the connection is attained by read and write system calls.

A router is an application program. The router is installed in a PC to forward the frames to the WS's. The boundanes of all the frames are distributed to the router. On receiving the boundary of a frame, the router reads the frame from the frame buffer and submits the frame to the socket which is connected to a socket in the WS. Frame boundaries are lost during stages of processes between the sockets. Then a process in the WS receives frames sequenced without frame boundaries. The router, therefore, fulfills reserved fields in the frame to complete data structure in the frame before the submission. The data structure enables the process in the WS to restore the frame boundaries.

Plural identical PC's and WS's are installed in the system to control and to monitor the apparatus borne on a balloon. A lot of functions are required to be provided. In the system, the required functions are implemented by the union of the PC's and the WS's. The functions are divide to parts each of which operates rather independent of others, and the computers are assigned to realize individual parts. Programs, which implement the part of the functions, can be developed independently on each computer. The independence makes the program development easier.

One of the PC's is dedicated to monitor the status of the apparatus on the balloon. The status is sent periodically from the apparatus. A program on the PC shows the status on the screen. The program controls display of the status in a flexible way. Various modes of display are controlled interactively through a terminal. Moreover the program is capable of warning. The program scans the status, and if it finds anything outside prescribed allowance, the warning is issued on the screen.

The object of the experiment is to gather data of such events that satisfy prescribed conditions. Event data are sent at a fixed time interval to the ground station for a monitor purpose. The display of the event data helps understand the status of the apparatus. One of the PC's is devoted for the purpose. A program on the PC displays the tracks of the particles and associated data on the screen. The event display is of much use to bring and to maintain the apparatus under the best condition. The program supports facilities for the purpose. Modes of display and a time interval to refresh display are interactively controlled from a terminal.

Frames received by the process in the WS are submitted to various processes. They are concemed with the accumulation, the sorting, the histogramming and the presentation of the data carried by the frames. The address of the frame shows the destination and the content of the frame. The frame is called the message, the status or the event data frame according to the content of the frame. Transputers and microcomputers installed in the apparatus are sources of frames, and the frame includes a field to show the source. Message frames having the same source are grouped and displayed on individual windows. Temperatures are measured at various points in the apparatus. Voltages and pressures are similarly measured. They are carried by the status frames. A process for the status frames displays their time dependence for the individual points. Analysis routines are applied to event data. Results of the analysis are visually displayed on windows.

We would like to thank the staff of NSBF for their supports to our experiment. Thanks are also due to the people who are involved in BESS experiment.

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[4] M. Durand, M. Dadou and P. Malaterre, "Telecommande pour Balloons Longue Distance", Adv. Space Res. Vol. 7, No. 7, 1987, pp. 89-93.

[4] C. Bannelier and A. Soubrier, 'I Use of Telephone Data Link in Statosheric Balloon Flights", Adv. Space Res. Vol. 7, No. 7, 1987, pp. 93-96.

[3] Jesse Phillips, "Remote Data Communication and