Projects developed

• Free Phone: In order to test the ideas and algorithms around the transmission of audio data trough Internet, I have built an audio tool named ``Free Phone''. It is programmed in ``C'', with a GUI in Tcl/Tk. Some characteristics include: 1. Ability to have more than just one unicast and/or multicast sessions. 2. Implements RTP v2. 3. Available codecs PCMU, VADPCM, ADPCM @ 6,5,4,3 and 2 bits, GSM, LPC. 4. Redundancy mechanisms for lost packets reconstruction. 5. Signaling protocol to establish connections. 6. High quality audio with sampling rates that range from 8 KHz to 48 KHz. 7. Compatibility with RAT, VAT 4.x (in RTP mode), and soon with NeVoT.
• Ethernet driver: Taking an incomplete driver for the 3Com 3C509 Ethernet card, I made the modifications to fix some bugs and extend its capabilities. The main extension was the use of the early interruption facilities. The driver being that included in the FreeBSD 1.1.5.1 release.
• Fair Queueing Implementation: Motivated by the need to evaluate the impact of the packet scheduling policy over the end to end delay, jitter and lost process of audio packets while going trough a router, I build up a platform to compare the Fair Queueing policy against FIFO. The environment was a test network of PCs running the UNIX like operating system FreeBSD.
• Gas Station Control System: The goal was to create a system able to control the gas pumps trough a RS-422 interface, the (proprietary) magnetic card readers (MCR) linked together with a RS-485 bus, and the data base for validation and storage of transactions. The configuration was a PC-AT (data base and graphical user interface), an embedded card based on the Intel 80188 microprocessor (for the pump and MCR's control), and small systems based on the Intel 8031 micro-controller to which the MCRs where attached.
• Frame converter: The goal was to make the bridge between a host using SDLC frames and a PC using a proprietary frame's format. The converter was an autonomous card based on the Intel 8088 microprocessor.
• Kernel in ``C'': Software programmed in C and assembler languages for the Intel 8086 family of microprocessors. Starting from a previous kernel built in PL/M-86, the goal was to minimize the kernel's overhead, and to extend its capabilities, giving the kernel the ability to be used in a variety of hardware configurations.
• Packet Assembler/Disassembler: The programming was done using the PL/M-86 and ASM-86 languages. The work was divided in three parts: 1. To implement the norms X.3, X.28 and X.29; 2. Add the facilities of a keyboard and a LCD display for configuring the equipment; and 3. Make the integration of the link and network layers of X.25.
• Kernel in ``PL/M-86'': Software programmed in PL/M-86 and ASM-86 languages for the Intel 8086 family of microprocessors. We have 3 kind of processes: 1. Normal processes scheduled by priority (once a process get the CPU it releases it once it finish its work, voluntarily or at the next blocking primitive); 2. Periodic precesses; and 3. Processes activated by a timer. The kernel provides: 1. the process' control; 2. the process communication trough channels; 3. the process synchronization trough semaphores; 4. the dynamic control of memory; and 5. the timers. It was though for applications demanding good response times in modest environments (.i.e. 8086).
• Control Processor: Design and construction of a card based on the Intel 8086 microprocessor and the minimal software for controlling the hardware of the data switch. Such a software gives a reduced set of services (e.g. create and delete connections). The heart of the data switch being a commutation matrix with 32 RS-232 non blocking ports. It is worth to mention that this switch was though to allow the resource sharing (ports to a main frame, printers, plotters, etc.) for small centers with a relatively small number of equipments all them provided with at least one RS-232 port.