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+DEC 21140 Driver
+DEC 21240 Driver Introduction
+.. COMMENT: XXX add back in cross reference to list of boards.
+One aim of our project is to port RTEMS on a standard PowerPC platform.
+To achieve it, we have chosen a Motorola MCP750 board. This board includes
+an Ethernet controller based on a DEC21140 chip. Because RTEMS has a
+TCP/IP stack, we will
+have to develop the DEC21140 related ethernet driver for the PowerPC port of
+RTEMS. As this controller is able to support 100Mbps network and as there is
+a lot of PCI card using this DEC chip, we have decided to first
+implement this driver on an Intel PC386 target to provide a solution for using
+RTEMS on PC with the 100Mbps network and then to port this code on PowerPC in
+a second phase.
+The aim of this document is to give some PCI board generalities and
+to explain the software architecture of the RTEMS driver. Finally, we will see
+what will be done for ChorusOs and Netboot environment .
+Document Revision History
+*Current release*:
+- Current applicable release is 1.0.
+*Existing releases*:
+- 1.0 : Released the 10/02/98. First version of this document.
+- 0.1 : First draft of this document
+*Planned releases*:
+- None planned today.
+DEC21140 PCI Board Generalities
+.. COMMENT: XXX add crossreference to PCI Register Figure
+This chapter describes rapidely the PCI interface of this Ethernet controller.
+The board we have chosen for our PC386 implementation is a D-Link DFE-500TX.
+This is a dual-speed 10/100Mbps Ethernet PCI adapter with a DEC21140AF chip.
+Like other PCI devices, this board has a PCI device’s header containing some
+required configuration registers, as shown in the PCI Register Figure.
+By reading
+or writing these registers, a driver can obtain information about the type of
+the board, the interrupt it uses, the mapping of the chip specific registers, ...
+On Intel target, the chip specific registers can be accessed via 2
+methods : I/O port access or PCI address mapped access. We have chosen to implement
+the PCI address access to obtain compatible source code to the port the driver
+on a PowerPC target.
+.. COMMENT: PCI Device's Configuration Header Space Format
+.. image:: images/PCIreg.jpg
+.. COMMENT: XXX add crossreference to PCI Register Figure
+On RTEMS, a PCI API exists. We have used it to configure the board. After initializing
+this PCI module via the ``pci_initialize()`` function, we try to detect
+the DEC21140 based ethernet board. This board is characterized by its Vendor
+ID (0x1011) and its Device ID (0x0009). We give these arguments to the``pcib_find_by_deviceid``
+function which returns , if the device is present, a pointer to the configuration
+header space (see PCI Registers Fgure). Once this operation performed,
+the driver
+is able to extract the information it needs to configure the board internal
+registers, like the interrupt line, the base address,... The board internal
+registers will not be detailled here. You can find them in *DIGITAL
+Semiconductor 21140A PCI Fast Ethernet LAN Controller
+- Hardware Reference Manual*.
+.. COMMENT: fix citation
+RTEMS Driver Software Architecture
+In this chapter will see the initialization phase, how the controller uses the
+host memory and the 2 threads launched at the initialization time.
+Initialization phase
+The DEC21140 Ethernet driver keeps the same software architecture than the other
+RTEMS ethernet drivers. The only API the programmer can use is the ``rtems_dec21140_driver_attach````(struct rtems_bsdnet_ifconfig \*config)`` function which
+detects the board and initializes the associated data structure (with registers
+base address, entry points to low-level initialization function,...), if the
+board is found.
+Once the attach function executed, the driver initializes the DEC
+chip. Then the driver connects an interrupt handler to the interrupt line driven
+by the Ethernet controller (the only interrupt which will be treated is the
+receive interrupt) and launches 2 threads : a receiver thread and a transmitter
+thread. Then the driver waits for incoming frame to give to the protocol stack
+or outcoming frame to send on the physical link.
+Memory Buffer
+.. COMMENT: XXX add cross reference to Problem
+This DEC chip uses the host memory to store the incoming Ethernet frames and
+the descriptor of these frames. We have chosen to use 7 receive buffers and
+1 transmit buffer to optimize memory allocation due to cache and paging problem
+that will be explained in the section *Encountered Problems*.
+To reference these buffers to the DEC chip we use a buffer descriptors
+ring. The descriptor structure is defined in the Buffer Descriptor Figure.
+Each descriptor
+can reference one or two memory buffers. We choose to use only one buffer of
+1520 bytes per descriptor.
+The difference between a receive and a transmit buffer descriptor
+is located in the status and control bits fields. We do not give details here,
+please refer to the \[DEC21140 Hardware Manual].
+.. COMMENT: Buffer Descriptor
+.. image:: images/recvbd.jpg
+Receiver Thread
+This thread is event driven. Each time a DEC PCI board interrupt occurs, the
+handler checks if this is a receive interrupt and send an event “reception”
+to the receiver thread which looks into the entire buffer descriptors ring the
+ones that contain a valid incoming frame (bit OWN=0 means descriptor belongs
+to host processor). Each valid incoming ethernet frame is sent to the protocol
+stack and the buffer descriptor is given back to the DEC board (the host processor
+reset bit OWN, which means descriptor belongs to 21140).
+Transmitter Thread
+This thread is also event driven. Each time an Ethernet frame is put in the
+transmit queue, an event is sent to the transmit thread, which empty the queue
+by sending each outcoming frame. Because we use only one transmit buffer, we
+are sure that the frame is well-sent before sending the next.
+Encountered Problems
+On Intel PC386 target, we were faced with a problem of memory cache management.
+Because the DEC chip uses the host memory to store the incoming frame and because
+the DEC21140 configuration registers are mapped into the PCI address space,
+we must ensure that the data read (or written) by the host processor are the
+ones written (or read) by the DEC21140 device in the host memory and not old
+data stored in the cache memory. Therefore, we had to provide a way to manage
+the cache. This module is described in the document *RTEMS
+Cache Management For Intel*. On Intel, the
+memory region cache management is available only if the paging unit is enabled.
+We have used this paging mechanism, with 4Kb page. All the buffers allocated
+to store the incoming or outcoming frames, buffer descriptor and also the PCI
+address space of the DEC board are located in a memory space with cache disable.
+Concerning the buffers and their descriptors, we have tried to optimize
+the memory space in term of allocated page. One buffer has 1520 bytes, one descriptor
+has 16 bytes. We have 7 receive buffers and 1 transmit buffer, and for each,
+1 descriptor : (7+1)*(1520+16) = 12288 bytes = 12Kb = 3 entire pages. This
+allows not to lose too much memory or not to disable cache memory for a page
+which contains other data than buffer, which could decrease performance.
+ChorusOs DEC Driver
+Because ChorusOs is used in several Canon CRF projects, we must provide such
+a driver on this OS to ensure compatibility between the RTEMS and ChorusOs developments.
+On ChorusOs, a DEC driver source code already exists but only for a PowerPC
+target. We plan to port this code (which uses ChorusOs API) on Intel target.
+This will allow us to have homogeneous developments. Moreover, the port of the
+development performed with ChorusOs environment to RTEMS environment will be
+easier for the developers.
+Netboot DEC driver
+We use Netboot tool to load our development from a server to the target via
+an ethernet network. Currently, this tool does not support the DEC board. We
+plan to port the DEC driver for the Netboot tool.
+But concerning the port of the DEC driver into Netboot, we are faced
+with a problem : in RTEMS environment, the DEC driver is interrupt or event
+driven, in Netboot environment, it must be used in polling mode. It means that
+we will have to re-write some mechanisms of this driver.
+List of Ethernet cards using the DEC chip
+Many Ethernet adapter cards use the Tulip chip. Here is a non exhaustive list
+of adapters which support this driver :
+- Accton EtherDuo PCI.
+- Accton EN1207 All three media types supported.
+- Adaptec ANA6911/TX 21140-AC.
+- Cogent EM110 21140-A with DP83840 N-Way MII transceiver.
+- Cogent EM400 EM100 with 4 21140 100mbps-only ports + PCI Bridge.
+- Danpex EN-9400P3.
+- D-Link DFE500-Tx 21140-A with DP83840 transceiver.
+- Kingston EtherX KNE100TX 21140AE.
+- Netgear FX310 TX 10/100 21140AE.
+- SMC EtherPower10/100 With DEC21140 and 68836 SYM transceiver.
+- SMC EtherPower10/100 With DEC21140-AC and DP83840 MII transceiver.
+ Note: The EtherPower II uses the EPIC chip, which requires a different driver.
+- Surecom EP-320X DEC 21140.
+- Thomas Conrad TC5048.
+- Znyx ZX345 21140-A, usually with the DP83840 N-Way MII transciever. Some ZX345
+ cards made in 1996 have an ICS 1890 transciver instead.
+- ZNYX ZX348 Two 21140-A chips using ICS 1890 transcievers and either a 21052
+ or 21152 bridge. Early versions used National 83840 transcievers, but later
+ versions are depopulated ZX346 boards.
+- ZNYX ZX351 21140 chip with a Broadcom 100BaseT4 transciever.
+Our DEC driver has not been tested with all these cards, only with the D-Link
+- *[DEC21140 Hardware Manual] DIGITAL, *DIGITAL
+ Semiconductor 21140A PCI Fast Ethernet LAN Controller - Hardware
+ Reference Manual**.
+- *[99.TA.0021.M.ER]Emmanuel Raguet,*RTEMS Cache Management For Intel**.