Homework 10 Software Design Considerations
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1. first picture in the directory It then tries to connect to the IP address and port combination passed via the command line When connected it constantly tries to read in command data from the Rabbit Once the Rabbit server sends it a command it executes the corresponding command and then returns to reading commands The nextpic command simply changes the picture pointer to the next available picture file The prevpic command changes the picture pointer to the previous available picture file The getpicname command from the Rabbit causes the PC to respond by sending a sendpicname command back to the Rabbit with the name of the file pointed to by the picture pointer as the data field When the PC receives the recy command it must proceed to send the entire picture in order to the Rabbit As it sends picture data it checks to see if another command has been received Other commands can interrupt this command and take over execution This is done so the user does not have to wait for an entire picture to display to cycle through to a different picture In order to send a picture the current picture file is broken down into pixels Each pixel is converted from 24 bits per pixel to 15 bits per pixel because the Epson can only support a maximum of 15 bits per pixel without using a color table First the sendnewpic command is sent to the Rabbit that resets the Epson s address to the first address in the frame buffer and2. loads the first pixel color data Every picture thereafter uses the sendnextpixel command to implicitly increment the address pointer as well as load in the corresponding pixel color data TCP IP PC Client Flowchart Scan local directory for picture files Create list of pictures and current picture pointer Connect to Rabbit Server designated by command line arguments Update current Monitor incoming picture file pointer network data continue monitoring network Nextpic prevpic Decode command Send picture data pixel Rabbit Multitasking Flowchart Copy any available incoming network data to indata No yield control Abort Control No Control Try and extract a PC command from buffer indata Yes abort control No yield control Update Epson s Frame Buffer with the attached address and pixel data Send corresponding command via Network to the PC No Abort Control Send corresponding command via Network to PC No Abort control Debounce Button Inputs References 1 Richard Stevens Unix Network Programming Networking APIs Sockets and XTI Upper Saddle River NJ Prentice Hall PTR 1998 2 Dynamic C TCP IP User s Manual Davis CA Z World Inc 2002
3. number of bytes the included command occupies There are also 99 66 99 66 four commands sent to the Rabbit sendpicname sendnewpic sendnextpixel and sendpixeladdress Sendpicname includes a text string that is the filename as it is stored on the PC Sendnewpic resets the current address pointer to the frame buffer on the Epson graphics controller to the first address and sends the first pixel s color data Sendnextpixel increments the frame buffer address pointer and sends the corresponding color data for that pixel Sendpixeladdress sets the frame buffer address pointer to an absolute address and then sends the color data for that pixel Summary of TCPAP Communication Protocol Incoming Rabbit packets Incoming PC packets Packets can include Commands and Data Null terminated commands Total length used to distinguish between consecutive Commands Include getpicname nextpic prevpic packets stored in the Rabbit s temporary buffer Command length used to separate the Command from Data Commands include sendpicname sendnewpic sendnextpixel and sendpixeladdress The Rabbit program consists of several programming modules which are actually costatements that implement the cooperative multitasking environment described earlier The first costatement constantly runs the tcp_tick command This is done to perform all the necessary low level TCP IP bookkeeping The sec
4. Homework 10 Software Design Considerations Group Number 12 Phillip Boone Introduction The Digital Picture Box functionally is used to display to a VGA monitor a database of pictures stored remotely on a personal computer via the Internet The status LED is used to indicate the device has power and also indicates when a picture is being transferred The push buttons are used to cycle through the pictures stored on a remote PC The remote control will have the same functionality as the push buttons The picture box is designed to connect directly to any standard VGA monitor or LCD screen The box must have a custom TCP IP server running with it s own custom image transfer protocol in order for the data exchange with the PC to work The Digital Picture Box design basically consists of a small cubicle casing that has push buttons and a status LED on the front On the right side of the casing there is a VGA connector on the left side there is a RJ 45 network connector and on the rear there is a power connector The Digital Picture Box requires two major software projects the Rabbit 3000 TCP IP server and the PC picture client From a network perspective the Rabbit is a server because the Rabbit has no way of inputting an IP address with its limited push buttons and IR input However the PC client acts as a file server because all of the picture files are stored on the PC s hard drive I plan to use a custom TCP IP protocol fo
5. ction The abort function is very similar to yield however when the process regains control it starts execution at the beginning of the costatement block Software Design Narrative In order for the PC program module and Rabbit module to successfully communicate together they must obey some type of protocol It was decided to implement a custom TCP IP Picture Frame Protocol The packet data that is sent from the Rabbit to the PC file server is just plain text ending in a null terminating character The Rabbit only needs to send four commands to the PC nextpic 99 66 prevpic getpicname and recv Nextpic tells the PC to change it s current file pointer to the next available picture file Prevpic tells the PC to change it s current file pointer to the previous picture file Getpicname requests the name of the current picture file Recv tells the file server to begin sending the current picture file The packet data that is sent from the PC to the Rabbit requires the use of two length fields The Rabbit dumps all of the incoming data into a temporary buffer A total length field that is placed at the beginning of each packet is necessary to distinguish between consecutive packets dumped into the buffer Once a single packet is extracted from the buffer it is necessary to separate the included command from binary data The second part of each packet is a command length integer which is the
6. h the menu The next and previous buttons now cycle through different menu options The function button selects the highlighted menu option The Power button exits out of the overlay menu system Summary of Rabbit Programming Modules Programming Module Description tcp_tick Constantly called to perform all necessary low level network bookkeeping Listens to the network port When connected it drops all incoming data to a circular buffer if incoming _tcp __ possible Monitors the infrared port If a command is detected the corresponding command is sent via monitorIR TCP IP to the PC Monitors the button input If a command is detected the corresponding command is sent via monitor buttons TCP IP to the PC Decodes the data stored in the circular buffer The pixel data at the corresponding address is decodePCdata_ sent to the Epson controller A basic menu system is displayed All input buttons are now directed to this function while in overlay mode jthe menu system The final major programming module is the TCP IP client that can run on any standard Linux PC It is acommand line program that takes two arguments IP address of the Rabbit and port number of the Rabbit server The IP address argument can actually be a domain name that will automatically be resolved on execution The program begins by scanning the local directory for picture files in the ppm format It has a built in picture pointer that starts off pointing to the
7. ond costatement incoming_tcp starts listening on port 39 for any TCP IP connections Once it detects a connection it takes all incoming data and drops it into a temporary circular buffer called indata If indata is full it yields control until there is enough space to put the data into the circular buffer This is repeated while the PC is connected Once the PC disconnects the Rabbit goes back to listening on the network port The third costatement monitorIR polls the IR input pins two samples at a time When an IR remote button is pressed the logic value on the output of the IR pin changes This can be detected when two consecutive samples are opposite logic values indicating a recent logic change Whenever a button press is detected the Rabbit sends the corresponding command to the PC if a network connection is present The fourth costatement monitor_buttons is the same as monitorIR except it debounces the switch inputs and sends the corresponding command to the PC if there is a network connection The switches are debounced by taking three samples of each input pin There is a delay of 50 ms inserted in between each sample via the DelayMs function that automatically configures a timer interrupt Once three samples agree the logic value of the samples is compared with the previously obtained agreeing samples If a logic value zero was followed by a logic value one indicating a rising edge then a button p
8. r communication that is described later The Rabbit 3000 micro controller must be able to listen on the RJ 45 port for any incoming connections Once the client PC program connects the Rabbit will control what file to transfer as well as when to transfer it It will have to forward the data to the Epson graphics controller in a timely fashion I plan to setup a simple multitasking environment that I explain in the Software Design Narrative section which consists of several modules The first module incoming_tcp will monitor the TCP IP connection and if active dump all data to a large circular buffer The second module decodePCdata will decode the instruction stored in the circular buffer and then execute the corresponding data transfer command on the Epson graphics controller The third module monitor_buttons debounces the input buttons It sends the corresponding command via TCP IP to the PC if a different image needs to be fetched or updates text overlay if in text overlay mode The fourth module monitor_IR performs the same function as monitor_buttons but receives the command from the IR remote instead of push buttons Finally the last module overlay_mode will execute a series of overlay setup menus stored on the Rabbit The PC client software is responsible for converting the picture data to a useable format for the Epson graphics controller sending the picture data in order compiling a picture lib
9. rary and keeping track of the current displayed picture It will constantly monitor any incoming rabbit control statements and perform the corresponding command It either needs to execute commands that transfer a picture or update the pointer to the current picture Software Design Considerations The Rabbit 3000 micro controller has several general design considerations Since the controller comes with a Dynamic C compiler it automatically handles the memory mapping and management at compile time The compiler also sets up the necessary startup code so the downloaded program will automatically execute on power up There is also support for a simple multitasking environment included with the compiler The current proposed implementation for sending address information to the Epson controller is somewhat inefficient Transferring a single picture could take a fair amount of time It was decided that in order to create a responsive software interface we should take advantage of the built in multitasking functions to easily interrupt a picture transfer in progress There are three basic C functions that implement a cooperative multitasking environment First a costatement designates a piece of code to a single running process Within that process it has the option to call the yield function This gives up control to the next process When the process that called yield obtains control again it returns to the line of code after the yield fun
10. ress was successfully detected The fifth costatement decodePCdata consumes data contained in the circular buffer one command at a time Each decoded command is stored in a temporary location The command length is read in and then the entire command is read in if possible If it is not possible to decode an entire command control is yielded to the next process Once the command is decoded the proper address is sent to the address bus of the PLD s that interface with the Epson graphics controller The address is clocked in 8 bits at a time for three clock cycles until the entire address is present The 15 bit color data is then sent out on the data bus and the Rabbit generates the necessary signals to load the current pixel into the frame buffer of the Epson graphics controller The last costatement overlay_mode is only called when the Function button is pressed This will bring up a menu system that is overlaid on the VGA display A set of fonts is stored into the flash memory of the Rabbit A basic function print_character will output the character stored in the font data at a specific point on the screen The function will require an address argument to specify the point location and a character argument This basic function is used to display the entire character menu The remote controller and push buttons now are polled in the same fashion as described in the earlier functions but they now are used to navigate throug
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