Implementation of USB

The proposed solution to establish serial communication using USB protocol is to design a circuit that can handle this communication protocol and interfaced it to the Microcontroller. By looking for a suitable ways to achieve this task two approaches for USB protocol implementation were found:

1- Using a Single IC chip for RS232 to USB conversion with a given Microcontroller circuit equipped with a built-in UART.

2- Using a single chip parallel to USB conversion with any Microcontroller circuit, only one 8-bits port is needed.

But as extra work to improve the design we start thinking to develop a soft core for the USB protocol that can be integrated with a given Microcontroller core.

In this section each one of the above approaches will be explained in details and by the end of this chapter the chosen one will be applied.

4.2.1 USB Cores for FPGA

Any USB device should be able to have interface with any industry standard Microcontroller on one side and with any standard USB transceiver on the other side.

The core should implement all functionality required at physical (digital) layer and protocol layer of USB specification.

4.2.1.1 Physical Layer This layer is responsible of:

- Synchronization (DPLL) - NRZI decoding / encoding - Bit stuffing /un stuffing - Parallel to serial conversion - serial to Parallel conversion

this layer is simply divided into a transmitter and receiver , the transmitter converts the data from Parallel to serial , stuff zero bits if needed then performs encoding process .The receiver performs decoding process, un-stuff zeros if needed then converts the data from serial to Parallel

4.2.1.2 Protocol layer

This layer is the layer responsible for understanding the host requests and doing the proper actions. To develop this layer all fields and packets which is descried in chapter 2 for USB must be generated.

Several trials had been done during this work to get a working core for this layer. No dedicated block diagrams for this layer were available. On the other hand most of the available free cores either those written in Verilog, System C or even in VHDL have limited operational descriptions. Several efforts were done to put them in operation but unfortunately they did not work. By contacting the owners of these cores, some of them did not answer at all, while others demanded high price for their help. Other approach was to contact companies that supply soft cores with full documents. The obtained prices for USB cores are very high and out of the budget of this work. Also, they asked for some justifications from the university that this core will not be used in industrial applications or for developing any commercial product.

From the above it was concluded that we have to address the hardware solution as proposed to implement the USB circuit, and in this case two choices, as regarding the Microcontroller interfacing, are available:

1- Serial Interfacing to Microcontroller 2- Parallel Interfacing to microcontroller.

Both of these techniques will be introduced and analyzed.

4.2.2 Serial Interfacing to Microcontroller

This technique is the commonly used by most of the designers. Most of the available off- shelf Microcontroller has built-in UART circuit. The RS 232 serial interface is a well known serial data link, understood by most of the designers and almost all serial interfaces for peripheral devices outside the physical layer of a given Data Terminal Equipments (DTE) are built using this interface [12]. So, the most straight forward solution from the IC,s manufacturing companies was to develop a single chip that converts between the RS232 and the USB physical and protocol layers. Typical example for this solution is that given by Maxim [13] that impalements USB interface with the PIC Microcontroller by using the FT 232BM as shown in Figure 4.1

Several other implementations are also available in literature. One disadvantage of this solution is the limitation of speed imposed by the maximum data rates supported by the RS232 serial data link [3]. The USB physical circuit can support higher data rates and this may be accomplished by going to parallel interfacing.

4.2.3 Parallel Interfacing to Microcontroller

Recently, introduced in the market some IC chips that work as USB peripheral controller with parallel interface such as the PDIUSBD12 from Philips semiconductor [14] and the FT245R from FDTI [15]. Since we have parallel interface (ports) in PicoBlaze Microcontroller Core that may provide high connection speed (compared to Serial) FT245R parallel to USB chip will be used (see appendix C for its data sheet). Figure 4.4 gives the block diagram of this circuit where we can identify the following blocks:

4.3 Hardware verification of Microcontroller Core with USB interface

From the previous section it clearly that using a USB chip with Parallel Interfacing can be used and eliminate the speed restriction of using USB chip with serial interface. In chapter 3 a PicoBlaze core for Microcontroller was selected to be the used Microcontroller in this study

In order to test the PicoBlaze micro controller core with the USB chip FT245R an emulation testing board is needed. This board enables us to download the microcontroller code onto the FPGA chip, make all the possible connections with the FFT245R chip and provide USB standard socket. This board consists of four parts:

Part 1: FPGA test and development board containing the target FPGA chip with all the necessary hardware and software facilities that enable downloading, testing and verifying a given VHDL code.

NEXYSII board was chosen and supplied from Digilent Company [16], one of the most popular companies for manufacturing development boards. Its schematic diagram is given in appendix D, however, its Data sheet is not completed yet and it is under preparation figure 4.3 showing this board.

Part 2 : An extension board (FX2BB ) that can be attached to the board of part1 to allow adding more hardware components needed for system building .

Part 3: FT245R USB chip

Part 4: the Physical implementation of the USB B jack

A proposed test configuration is given in Figure 4.4

Figure 4.4: proposed block diagram for Microcontroller with USB

4.4 Experimental work

The block diagram given in Figure 4.4 is completely built in the laboratory and used to verify the hardware functionality of the proposed design. The test is divided into three steps:

Step1: testing the PicoBlaze VHDL code as written to impalement the Microcontroller on NEXYSII board

Step 2: Integrate the hardware built in step1 with the FT245R chip and prepare the USB physical connection.

Step 3: Writing the necessary VHDL codes to achieve the proposed solution to get Microcontroller with USB interface

Step 4: Testing the overall circuit by establishing a serial communication connection with the USB interface of any computer host using familiar communication package like Hyper Terminal under windows [26].

4.4.1 Hardware verification of PicoBlaze testing code

In section 3.3.5 one basic program to read switched and update LED’s accordingly for PicoBlaze Microcontroller core was simulated using Aldec tool, now we need to test this program in real signal environment. Since Xilinx FPGA will be used here, another tool from Xilinx (ISE 9.1) [11] is recommended for programming and downloading. This version was used during this study.

By synthesizing the codes in section 3.3.5 and downloading this code into the target FPGA on board NEXYSII the circuit may be experimentally tested .figure 4.5 shows that the code given in section 3.3.5 is verified experimentally and it is clear that the LEDs are reflecting the status of the switches

Figure 4.5: Hardware verification for PicoBlaze code

4.4.2 Integrating the FPGA board (NEXYSII) with (FT245R) USB Chip

Integration of the Microcontroller PicoBlaze core downloaded on the FPGA with the USB Chip (FT245R) needs the following steps:

1- Doing a correct assignment for the FPGA pins to handle the input output ports and other control pins, in this board version some pins assigned only for serial

2- The pins which have been assigned are already connected to the extended board FX2BB connector, since NEXYSII is a new board and its datasheet is still under preparation, the schematic of the board and the layout should be used to trace the connection.

3- Wiring the connections of the extended board FX2BB to the USB chip FT245R.

Figure 4.6 shows on board connection of the system.

Figure 4.3: Microcontroller with USB on board Figure 4.6: Microcontroller with USB on board

4.4.3 Assembly and VHDL codes for Microcontroller with USB

As can be seen in figure 4.5 the Hardware is completed and need to be tested, so the next step is to write an assembly code for PicoBlaze Microcontroller and VHDL code for all the system.

4.4.3.1 PicoBlaze assembly program for Microcontroller with USB

This program reads the status value of 8 switches in hex format. This value is then transferred to the attached PC through the built USB interface and displayed using the Hyper Terminal under windows as the ASCII equivalent of read HEX value. On the same time any character entered by the key board of the PC through the Hyper Terminal window will be displayed on the 8 LED display of the NEXYSII board. A reset function of all LED is also available.

This assembly program contains the following parts:

1- the definition of all constants in addition to the ASCII table

2- USB communication routines

This routines is the main part of the assembly program since it will handle the reading and writing from/to the USB chip.

a- Sending to USB

Microcontroller will transmit data to USB chip using this routine and at the beginning of this routine the program will read the control port then test the transmit buffer is it empty or full if empty the data port will be loaded by the data and the write to USB chip bit in the control port should be set send data to the USB chip and finally the control port should be rest to be ready.

b- Read from USB

In this routine the Microcontroller will read from the USB chip and this will be done by testing if there is a data in data buffer of the chip or not and read it if existing then reset the Zero flag to use it again in other process

3- the main program

This part will contain the sending menu text and waiting the input of the user to choose reading switches and update LED’s or reset the LED’s

4- reading Switches routine

To read switches value and send it to the USB chip to show it in the terminal program

5- Updating LED’s routines

To Update LED’s with the Value which the user interred

6- Text messages

These routines will send the text messages to the terminal such as menus and it will be done by sending character by character

For all the program (See appendix E)and this program will be converted to ROM VHDL code using PicoBlaze assembler which was provided by Xilinx and will be added to the VHDL code in next section to complete all VHDL codes that are needed to test the proposed solution

4.4.3.2 VHDL code for testing Microcontroller with USB interface

The next step is to complete the system VHDL code (see appendix F) and download it to on board FPGA

Figure 4.7 gives the block diagram of VHDL code

Figure 4.7: Block diagram of VHDL code The top level code is contains of the following parts:

1- the tope level entity that representing the black block in figure 4.7 and assigning the input and output of the system as following

2- declaration of (KCPSM3) the PicoBlaze Microcontroller (see appendix J for the VHDL code for it )

3- declaration of the ROM

5- Signals used to connect KCPSM3 to USB/FIFO interface and LED’s/Switches

6- Switches, and LEDs connections and USB/FIFO control register connections

8- KCPSM3 output ports

9- The FPGA will drive USB data bus all the time and need to be released when reading from USB chip

All these codes (the assembly code in ROM which explained in section 4.4.3.1 and the above Top VHDL code) are synthesized and downloaded to the FPGA on NEXYSII board

4.4.4 Testing the overall circuit

In previous sections the Overall circuit is built on board and the assembly program was also written. The all VHDL codes are the downloaded on the FPGA, now the circuit is ready to be tested.

On power starting, the Microcontroller sends the menu shown in Figure 4.8 to the terminal program in the PC (Hyper Terminal for example), and keep waiting for user response. The user responds by either input 1 or 2 or 3.

Figure 4.8: Hyper Terminal showing the program Menu

By pressing 1 the program will read the switch value which is in this example 30HEX and showing character 0 as the ASCII code equivalent to 30 HEX.

By pressing 2 the program will ask user to enter any character by pressing a key in the keyboard. The HEX value equivalent to the ASCII code of the pressed key will be displayed on the led display. In this example key corresponds to Num 1 was pressed and the LED display is showing 31 HEX which is the equivalent ASCII code.

Figure 4.9: Hyper Terminal window program execution

Typical real time run results are given in Figs 4.9 which gives the Hyper Terminal window during program execution. Figure 4.10 shows the status of the 8 switches read by the program and the resulted LED display after program execution.

From previous results the proposed circuit was designed and implemented and gave expected results and this circuit achieved a design of Microcontroller with USB interface.

Most of the M2M Mobile modules available in the market are still having serial interface type RS232; while Modern PC’s and laptops are going to use high speed USB interfaces rather than RS232 (Most of the Laptops available now in the market do not have any RS232). So, in next chapter the M2M Mobile modules available in the Ericsson Lab [1] will be integrated with the above described Microcontroller system to provide users with a complete M2M Mobile modules having USB interface.