linux-sg2042/Documentation/DocBook/z8530book.tmpl

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<book id="Z85230Guide">
 <bookinfo>
  <title>Z8530 Programming Guide</title>
  
  <authorgroup>
   <author>
    <firstname>Alan</firstname>
    <surname>Cox</surname>
    <affiliation>
     <address>
      <email>alan@lxorguk.ukuu.org.uk</email>
     </address>
    </affiliation>
   </author>
  </authorgroup>

  <copyright>
   <year>2000</year>
   <holder>Alan Cox</holder>
  </copyright>

  <legalnotice>
   <para>
     This documentation is free software; you can redistribute
     it and/or modify it under the terms of the GNU General Public
     License as published by the Free Software Foundation; either
     version 2 of the License, or (at your option) any later
     version.
   </para>
      
   <para>
     This program is distributed in the hope that it will be
     useful, but WITHOUT ANY WARRANTY; without even the implied
     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
     See the GNU General Public License for more details.
   </para>
      
   <para>
     You should have received a copy of the GNU General Public
     License along with this program; if not, write to the Free
     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
     MA 02111-1307 USA
   </para>
      
   <para>
     For more details see the file COPYING in the source
     distribution of Linux.
   </para>
  </legalnotice>
 </bookinfo>

<toc></toc>

  <chapter id="intro">
      <title>Introduction</title>
  <para>
	The Z85x30 family synchronous/asynchronous controller chips are
	used on a large number of cheap network interface cards. The
	kernel provides a core interface layer that is designed to make
	it easy to provide WAN services using this chip.
  </para>
  <para>
	The current driver only support synchronous operation. Merging the
	asynchronous driver support into this code to allow any Z85x30
	device to be used as both a tty interface and as a synchronous 
	controller is a project for Linux post the 2.4 release
  </para>
  </chapter>
  
  <chapter id="Driver_Modes">
 	<title>Driver Modes</title>
  <para>
	The Z85230 driver layer can drive Z8530, Z85C30 and Z85230 devices
	in three different modes. Each mode can be applied to an individual
	channel on the chip (each chip has two channels).
  </para>
  <para>
	The PIO synchronous mode supports the most common Z8530 wiring. Here
	the chip is interface to the I/O and interrupt facilities of the
	host machine but not to the DMA subsystem. When running PIO the
	Z8530 has extremely tight timing requirements. Doing high speeds,
	even with a Z85230 will be tricky. Typically you should expect to
	achieve at best 9600 baud with a Z8C530 and 64Kbits with a Z85230.
  </para>
  <para>
	The DMA mode supports the chip when it is configured to use dual DMA
	channels on an ISA bus. The better cards tend to support this mode
	of operation for a single channel. With DMA running the Z85230 tops
	out when it starts to hit ISA DMA constraints at about 512Kbits. It
	is worth noting here that many PC machines hang or crash when the
	chip is driven fast enough to hold the ISA bus solid.
  </para>
  <para>
	Transmit DMA mode uses a single DMA channel. The DMA channel is used
	for transmission as the transmit FIFO is smaller than the receive
	FIFO. it gives better performance than pure PIO mode but is nowhere
	near as ideal as pure DMA mode. 
  </para>
  </chapter>

  <chapter id="Using_the_Z85230_driver">
 	<title>Using the Z85230 driver</title>
  <para>
	The Z85230 driver provides the back end interface to your board. To
	configure a Z8530 interface you need to detect the board and to 
	identify its ports and interrupt resources. It is also your problem
	to verify the resources are available.
  </para>
  <para>
	Having identified the chip you need to fill in a struct z8530_dev,
	which describes each chip. This object must exist until you finally
	shutdown the board. Firstly zero the active field. This ensures 
	nothing goes off without you intending it. The irq field should
	be set to the interrupt number of the chip. (Each chip has a single
	interrupt source rather than each channel). You are responsible
	for allocating the interrupt line. The interrupt handler should be
	set to <function>z8530_interrupt</function>. The device id should
	be set to the z8530_dev structure pointer. Whether the interrupt can
	be shared or not is board dependent, and up to you to initialise.
  </para>
  <para>
	The structure holds two channel structures. 
	Initialise chanA.ctrlio and chanA.dataio with the address of the
	control and data ports. You can or this with Z8530_PORT_SLEEP to
	indicate your interface needs the 5uS delay for chip settling done
	in software. The PORT_SLEEP option is architecture specific. Other
	flags may become available on future platforms, eg for MMIO.
	Initialise the chanA.irqs to &amp;z8530_nop to start the chip up
	as disabled and discarding interrupt events. This ensures that
	stray interrupts will be mopped up and not hang the bus. Set
	chanA.dev to point to the device structure itself. The
	private and name field you may use as you wish. The private field
	is unused by the Z85230 layer. The name is used for error reporting
	and it may thus make sense to make it match the network name.
  </para>
  <para>
	Repeat the same operation with the B channel if your chip has
	both channels wired to something useful. This isn't always the
	case. If it is not wired then the I/O values do not matter, but
	you must initialise chanB.dev.
  </para>
  <para>
	If your board has DMA facilities then initialise the txdma and
	rxdma fields for the relevant channels. You must also allocate the
	ISA DMA channels and do any necessary board level initialisation
	to configure them. The low level driver will do the Z8530 and
	DMA controller programming but not board specific magic.
  </para>
  <para>
	Having initialised the device you can then call
	<function>z8530_init</function>. This will probe the chip and 
	reset it into a known state. An identification sequence is then
	run to identify the chip type. If the checks fail to pass the
	function returns a non zero error code. Typically this indicates
	that the port given is not valid. After this call the
	type field of the z8530_dev structure is initialised to either
	Z8530, Z85C30 or Z85230 according to the chip found.
  </para>
  <para>
	Once you have called z8530_init you can also make use of the utility
	function <function>z8530_describe</function>. This provides a 
	consistent reporting format for the Z8530 devices, and allows all
	the drivers to provide consistent reporting.
  </para>
  </chapter>

  <chapter id="Attaching_Network_Interfaces">
 	<title>Attaching Network Interfaces</title>
  <para>
	If you wish to use the network interface facilities of the driver,
	then you need to attach a network device to each channel that is
	present and in use. In addition to use the generic HDLC
	you need to follow some additional plumbing rules. They may seem 
	complex but a look at the example hostess_sv11 driver should
	reassure you.
  </para>
  <para>
	The network device used for each channel should be pointed to by
	the netdevice field of each channel. The hdlc-&gt; priv field of the
	network device points to your private data - you will need to be
	able to find your private data from this.
  </para>
  <para>
	The way most drivers approach this particular problem is to
	create a structure holding the Z8530 device definition and
	put that into the private field of the network device. The
	network device fields of the channels then point back to the
	network devices.
  </para>
  <para>
	If you wish to use the generic HDLC then you need to register
	the HDLC device.
  </para>
  <para>
	Before you register your network device you will also need to
	provide suitable handlers for most of the network device callbacks. 
	See the network device documentation for more details on this.
  </para>
  </chapter>

  <chapter id="Configuring_And_Activating_The_Port">
 	<title>Configuring And Activating The Port</title>
  <para>
	The Z85230 driver provides helper functions and tables to load the
	port registers on the Z8530 chips. When programming the register
	settings for a channel be aware that the documentation recommends
	initialisation orders. Strange things happen when these are not
	followed. 
  </para>
  <para>
	<function>z8530_channel_load</function> takes an array of
	pairs of initialisation values in an array of u8 type. The first
	value is the Z8530 register number. Add 16 to indicate the alternate
	register bank on the later chips. The array is terminated by a 255.
  </para>
  <para>
	The driver provides a pair of public tables. The
	z8530_hdlc_kilostream table is for the UK 'Kilostream' service and
	also happens to cover most other end host configurations. The
	z8530_hdlc_kilostream_85230 table is the same configuration using
	the enhancements of the 85230 chip. The configuration loaded is
	standard NRZ encoded synchronous data with HDLC bitstuffing. All
	of the timing is taken from the other end of the link.
  </para>
  <para>
	When writing your own tables be aware that the driver internally
	tracks register values. It may need to reload values. You should
	therefore be sure to set registers 1-7, 9-11, 14 and 15 in all
	configurations. Where the register settings depend on DMA selection
	the driver will update the bits itself when you open or close.
	Loading a new table with the interface open is not recommended.
  </para>
  <para>
	There are three standard configurations supported by the core
	code. In PIO mode the interface is programmed up to use
	interrupt driven PIO. This places high demands on the host processor
	to avoid latency. The driver is written to take account of latency
	issues but it cannot avoid latencies caused by other drivers,
	notably IDE in PIO mode. Because the drivers allocate buffers you
	must also prevent MTU changes while the port is open.
  </para>
  <para>
	Once the port is open it will call the rx_function of each channel
	whenever a completed packet arrived. This is invoked from
	interrupt context and passes you the channel and a network	
	buffer (struct sk_buff) holding the data. The data includes
	the CRC bytes so most users will want to trim the last two
	bytes before processing the data. This function is very timing
	critical. When you wish to simply discard data the support
	code provides the function <function>z8530_null_rx</function>
	to discard the data.
  </para>
  <para>
	To active PIO mode sending and receiving the <function>
	z8530_sync_open</function> is called. This expects to be passed
	the network device and the channel. Typically this is called from
	your network device open callback. On a failure a non zero error
	status is returned. The <function>z8530_sync_close</function> 
	function shuts down a PIO channel. This must be done before the 
	channel is opened again	and before the driver shuts down 
	and unloads.
  </para>
  <para>
	The ideal mode of operation is dual channel DMA mode. Here the
	kernel driver will configure the board for DMA in both directions.
	The driver also handles ISA DMA issues such as controller
	programming and the memory range limit for you. This mode is
	activated by calling the <function>z8530_sync_dma_open</function>
	function. On failure a non zero error value is returned.
	Once this mode is activated it can be shut down by calling the
	<function>z8530_sync_dma_close</function>. You must call the close
	function matching the open mode you used.
  </para>
  <para>
	The final supported mode uses a single DMA channel to drive the
	transmit side. As the Z85C30 has a larger FIFO on the receive
	channel	this tends to increase the maximum speed a little. 
	This is activated by calling the <function>z8530_sync_txdma_open
	</function>. This returns a non zero error code on failure. The
	<function>z8530_sync_txdma_close</function> function closes down
	the Z8530 interface from this mode.
  </para>
  </chapter>

  <chapter id="Network_Layer_Functions">
 	<title>Network Layer Functions</title>
  <para>
	The Z8530 layer provides functions to queue packets for
	transmission. The driver internally buffers the frame currently
	being transmitted and one further frame (in order to keep back
	to back transmission running). Any further buffering is up to
	the caller.
  </para>
  <para>
	The function <function>z8530_queue_xmit</function> takes a network
	buffer in sk_buff format and queues it for transmission. The
	caller must provide the entire packet with the exception of the
	bitstuffing and CRC. This is normally done by the caller via
	the generic HDLC interface layer. It returns 0 if the buffer has been
	queued and non zero values for queue full. If the function accepts
	the buffer it becomes property of the Z8530 layer and the caller
	should not free it.
  </para>
  <para>
	The function <function>z8530_get_stats</function> returns a pointer
	to an internally maintained per interface statistics block. This
	provides most of the interface code needed to implement the network
	layer get_stats callback.
  </para>
  </chapter>

  <chapter id="Porting_The_Z8530_Driver">
     <title>Porting The Z8530 Driver</title>
  <para>
	The Z8530 driver is written to be portable. In DMA mode it makes
	assumptions about the use of ISA DMA. These are probably warranted
	in most cases as the Z85230 in particular was designed to glue to PC
	type machines. The PIO mode makes no real assumptions.
  </para>
  <para>
	Should you need to retarget the Z8530 driver to another architecture
	the only code that should need changing are the port I/O functions.
	At the moment these assume PC I/O port accesses. This may not be
	appropriate for all platforms. Replacing 
	<function>z8530_read_port</function> and <function>z8530_write_port
	</function> is intended to be all that is required to port this
	driver layer.
  </para>
  </chapter>

  <chapter id="bugs">
     <title>Known Bugs And Assumptions</title>
  <para>
  <variablelist>
    <varlistentry><term>Interrupt Locking</term>
    <listitem>
    <para>
	The locking in the driver is done via the global cli/sti lock. This
	makes for relatively poor SMP performance. Switching this to use a
	per device spin lock would probably materially improve performance.
    </para>
    </listitem></varlistentry>

    <varlistentry><term>Occasional Failures</term>
    <listitem>
    <para>
	We have reports of occasional failures when run for very long
	periods of time and the driver starts to receive junk frames. At
	the moment the cause of this is not clear.
    </para>
    </listitem></varlistentry>
  </variablelist>
	
  </para>
  </chapter>

  <chapter id="pubfunctions">
     <title>Public Functions Provided</title>
!Edrivers/net/wan/z85230.c
  </chapter>

  <chapter id="intfunctions">
     <title>Internal Functions</title>
!Idrivers/net/wan/z85230.c
  </chapter>

</book>