Most wireless chip sets, such as wireless chipsets for 802.11 Wi-Fi applications, have a PCI bus to facilitate connection to an external processor. The reason for choosing the PCI bus is simply because there are a large number of PCs that may use wireless interfaces. However, this type of bus greatly limits the use of wireless chip sets in other applications, especially in portable devices. Even though some chipsets support miniPCI and Cardbus, they still exclude embedded controllers that are widely used. The bridging method can solve this problem.
Bridging method opens the door to the embedded controller
The bridge is just an interface between the PCI bus and the wireless transceiver and the target microcontroller local bus. If the processor bus supports an external device control bus and writes data directly to the processor's memory, this bridge can forward the DMA data transfer that was completed by the wireless chip set to the system RAM. However, if the processor does not support direct access to RAM, the processor must actively read and write data on the local bus. In order to effectively perform data transfer with the main memory, an addressable main memory is generally allocated to the wireless chip set through the descriptor chain, and the DMA controller in the wireless chip set must be able to access the descriptor, so that the bridge must be configured as a two-way cache. So that the wireless chipset can access the cache and descriptor chain via the PCI DMA, the processor accesses the other side of the cache through the local bus.
In addition, the local bus and PCI bus data streams must be synchronized with the bridge RAM cache. The RAM buffer capacity of the bridge is a key design factor, and the local bus latency between local bus transfer requests and processor execution is also a key design factor. For those processors that allow external devices to control the local bus, there is an excellent alternative to deliberately enabling the bridge to address the processor RAM directly. This gives a wireless chipset the ability to use DMA to transfer data directly through a transparent bridge. To the processor RAM, the processor is not burdening the data transmission and can use the standard PC software driver without modification.
Bridge implementation
The bridge can be customized with a single FPGA, and a better alternative would be to implement a commercial bridging solution. Because these bridges have low power consumption, small size, and personalized programmable logic that supports various processors, it is possible to provide a mixed-in solution that enables the concept of bridging to continue. Atheros, Intel and Renesas have already used such bridges in their products.
Potential for growth in application
Wireless chipsets with low-power bridges have found wider use. These include video surveillance, IP telephony, POS terminals, cars, GPS navigation, and remote control. Moreover, bridging methods and other wireless chipsets including WiMAX, Wireless USB, and Ultra-Wideband work very well, and the bridge is also an interface solution between hard disk drives and controllers. A typical example of this interface is Advanced Technology Attachment (ATA).
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