Abstract : This paper describes the construction method and implementation process of a wireless network card with an independent MAC layer protocol. An improved wireless LAN solution based on Intersil's PRISM 2 series wireless network card chipset is developed, using a DSP and CPLD to replace the MAC layer control chip, thus realizing the development of a wireless network card with an independent MAC layer protocol. Keywords : Wireless network card, PRISM2, TMS320VC5402, EPM7128AE, MAC protocol. With the growth of wireless network applications, various wireless access methods are emerging. Broadband wireless access systems based on the IEEE 802.11 wireless Ethernet standard have gained popularity due to their high data transmission rates (11-54 Mbps), fast network deployment, low operating costs, and quick return on investment. However, wireless network card chip suppliers only provide chipset solutions, which is extremely inconvenient for universities and research institutions researching MAC layer protocols for wireless LANs. The usual approach is to first develop their own MAC layer protocol software and then use a channel simulator to simulate this MAC layer protocol. The disadvantage of this approach is that it cannot be tested on a physical channel. This paper addresses this problem by using Intersil's PRISM2 series wireless LAN chipset solution. The MAC layer control chip is removed, and the TMS320VC5402 and PEM7128AE are used to control and exchange data with the other chips in the chipset, thus creating a wireless network card with an independent MAC layer protocol. 1. Wireless Network Card Solution The Intersil PRISM2 series wireless network card chipset and its main functions are listed in Table 1. Using this chipset, and based on the wireless LAN solution provided by Intersil, an IEEE 802.11b wireless network card can be easily built. Referring to the wireless LAN solution provided by Intersil, the author proposes a wireless network card solution with an independent MAC layer protocol, as shown in Figure 1. In this solution, the MAC layer control chip HFA3841 in the PRISM2 series chipset is removed, and the TMS320VC5402 and PEM7128AE are used to control and exchange data with the other chips in the PRISM2 series, thus building a wireless network card with an independent MAC layer protocol. 2. Wireless Network Card Interface Analysis According to the datasheet provided by Intersil and the interface relationships of its various chips, to build a wireless network card with an independent MAC layer protocol, the replacement chipsets TMS320VC5402 and EPM7128AE must have the following interface capabilities: ① Sufficient general-purpose I/O ports to connect to the various control pins of the chipset for set or clear operations, thereby ensuring the wireless network card is in the correct transmit/receive state. ② An SPI interface to initialize the registers in HFA3683, HFA3783, and HFA3861. It should be noted that for HFA3861, a 16-bit data transmission format is used, transmitting the most significant bit first; for HFA3783 and HFA3683, a 20-bit data transmission format is used, also transmitting the most significant bit first. ③ Continuous data transmission capability, enabling continuous data exchange with HFA3861. It should be noted that both the data reception and transmission clocks must be provided by HFA3861. According to the TMS320VC5402 chip datasheet, it features two multi-buffered synchronous serial ports (McBsp) supporting multiple interface standards and enabling high-speed bidirectional data transmission. Combining DMA with McBsp allows for the construction of an automatic serial data transmission channel without consuming CPU resources. Meanwhile, the EPM7128AE provides sufficient gate array units and I/O pins to perform set or clear operations on the wireless card's control pins. Furthermore, some 802.11b functions (such as backoff, timing, setting the NA bit, and CRC32 checksum) can be implemented within the EPM7128AE. Based on the above analysis, it is feasible to use the TMS320VC5402 and EPM7128AE to replace the HFA3841 for chip configuration, control, and data exchange, thus creating a wireless network card with its own MAC layer protocol. The interface relationship between the replacement chipset and the wireless network card chip is shown in Figure 2. In this design, serial port 0 of the TMS320VC5402 is responsible for initializing the registers of HFA3861, HFA3783, and HFA3683; serial port 1 is responsible for data exchange with HFA3861; and the I/O pins of the EPM7128AE are connected to the control pins of the chip for corresponding control operations. 3. Wireless Network Card Interface Implementation Based on the above analysis, controlling the wireless network card using the TMS320VC5402 and EPM7128AE mainly involves the following three steps: ① Initialization of the various registers of the wireless network card. Since the data transmission formats for initializing the HFA3861, HFA3783, and HFA3683 registers differ for the DSP, and the same serial port is used in this interface design, serial port 0 of the DSP must be initialized to the correct working mode before setting the registers. Furthermore, if the initialization values ​​of the registers are incorrect or the initialization order is incorrect, the initialization process cannot proceed normally, and the chips will not be in the correct working state. Due to the large number of registers involved, they will not be detailed here; please refer to the datasheet for further information. ② Control pin settings for the wireless network card. The configuration of the chip's control pins is mainly handled by the "Control Pin Configuration Module" within the CPLD. An example of the network card's data transmission process is provided, where the states of the relevant control pins are as shown in Figure 3. When the DSP wants to send data, it first sends a special configuration data CTRL_SND, which is decoded within the CPLD. Then, the "Transmit Data Control Pin Configuration Module" is activated, which handles the changes in the states of each control pin, thereby completing the data transmission. After data transmission is complete, each control pin should be set to receive mode within the first clock cycle. ③ Data transmission and reception of the wireless network card. The baseband data transmission and reception fluctuations of the wireless network card are shown in Figure 4. It uses a continuous data transmission mode, requiring the DSP's McBsp and DMA to work together to complete continuous data transmission. To ensure compatibility with general wireless network cards, the serial port needs to be set to an 8-bit data transmission mode, transmitting the high-order bits of the data first. One point to note is that both data transmission and reception require a clock provided by the HFA3861. However, the HFA3861 itself does not provide a frame synchronization signal. Therefore, frame synchronization needs to be generated within the CPLD using the clock provided by the HFA3861. However, simply generating one frame synchronization signal using eight clock cycles is not a viable method; otherwise, data misalignment will be severe. The correct approach is to fully utilize the TX_RDY and RX_RDY signals, allowing them to control the generation of a suitable frame synchronization signal. 4. Operation of the Wireless Network Card Finally, by operating the wireless network card according to the sequence shown in Figure 5, data transmission and reception can be performed correctly. 5. Conclusion Through interface timing analysis of the PRISM2 series wireless network card chipset, replacing the MAC layer control chip with a DSP and CPLD to construct a wireless network card with an independent MAC layer protocol has proven feasible. We successfully applied this in the 863 Major Project "Development of Wireless Mobile Self-Manufacturing Internet and its Experimental System," implementing an enhanced 802.11b MAC protocol.