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dev:devmanual [2006/07/16 09:35] stockholm |
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| ===== Writing an EtherBoot Driver ===== | ===== Writing an EtherBoot Driver ===== | ||
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| ==== Preliminaries ==== | ==== Preliminaries ==== | ||
| + | So Etherboot does not have a driver for your network adapter and you want to write one. You should have a good grasp of C, especially with respect to bit operations. You should also understand hardware interfacing concepts, such as the fact that the x86 architecture has a separate I/O space and that peripherals are commanded with ''out'' instructions and their status read with ''in'' instructions. A microprocessor course such as those taught in engineering or computer science curricula would have given you the fundamentals. (Note to educators and students in computer engineering: An Etherboot driver should be feasible as a term project for a final year undergraduate student. I estimate about 40 hours of work is required. I am willing to be a source of technical advice.) | ||
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| + | Next you need a development machine. This can be your normal Linux machine. You need another test machine, networked to the development machine. This should be a machine you will not feel upset rebooting very often. So the reset button should be in working condition. :-) It should have a floppy drive on it but does not need a hard disk, and in fact a hard disk will slow down rebooting. Alternatively, it should have another network adapter which can netboot; see discussion further down. Needless to say, you need a unit of the adapter you are trying to write a driver for. You should gather all the documentation you can find for the hardware, from the manufacturer and other sources. | ||
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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 ==== | ||
