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dev:devmanual [2006/07/16 09:37] stockholm |
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| ==== Background information ==== | ==== Background information ==== | ||
| + | There are several types of network adapter architecture. The simplest to understand is probably programmed I/O. This where the controller reads incoming packets into memory that resides on the adapter and the driver uses ''in'' instructions to extract the packet data, word by word, or sometimes byte by byte. Similarly, packets are readied for transmission by writing the data into the adapter's memory using ''out'' instructions. This architecture is used on the NE2000 and 3C509. The disadvantage of this architecture is the load on the CPU imposed by the I/O. However this is of no import to Etherboot (who cares how loaded the CPU is during booting), but will be to Linux. Next in the sophistication scale are shared memory adapters such as the Western Digital or SMC series, of which the WD8013 is a good example. Here the adapter's memory is also accessible in the memory space of the main CPU. Transferring data between the driver and the adapter is done with memory copy instructions. Load on the CPU is light. Adapters in this category are some of the best performers for the ISA bus. Finally there are bus mastering cards such as the Lance series for the ISA bus and practically all good PCI adapters (but not the NE2000 PCI). Here the data is transferred between the main memory and the adapter controller using Direct Memory Access. Setting up the transfers usually involves a sequence of operations with the registers of the controller. | ||
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| ==== Structure of the code ==== | ==== Structure of the code ==== | ||
| ==== Rom naming rules ==== | ==== Rom naming rules ==== | ||
