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Linux/Documentation/w1/masters/omap-hdq.rst

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  1 ========================================
  2 Kernel driver for omap HDQ/1-wire module
  3 ========================================
  4 
  5 Supported chips:
  6 ================
  7 HDQ/1-wire controller on the TI OMAP 2430/3430 platforms.
  8 
  9 A useful link about HDQ basics:
 10 ===============================
 11 http://focus.ti.com/lit/an/slua408a/slua408a.pdf
 12 
 13 Description:
 14 ============
 15 The HDQ/1-Wire module of TI OMAP2430/3430 platforms implement the hardware
 16 protocol of the master functions of the Benchmark HDQ and the Dallas
 17 Semiconductor 1-Wire protocols. These protocols use a single wire for
 18 communication between the master (HDQ/1-Wire controller) and the slave
 19 (HDQ/1-Wire external compliant device).
 20 
 21 A typical application of the HDQ/1-Wire module is the communication with battery
 22 monitor (gas gauge) integrated circuits.
 23 
 24 The controller supports operation in both HDQ and 1-wire mode. The essential
 25 difference between the HDQ and 1-wire mode is how the slave device responds to
 26 initialization pulse.In HDQ mode, the firmware does not require the host to
 27 create an initialization pulse to the slave.However, the slave can be reset by
 28 using an initialization pulse (also referred to as a break pulse).The slave
 29 does not respond with a presence pulse as it does in the 1-Wire protocol.
 30 
 31 Remarks:
 32 ========
 33 The driver (drivers/w1/masters/omap_hdq.c) supports the HDQ mode of the
 34 controller. In this mode, as we can not read the ID which obeys the W1
 35 spec(family:id:crc), a module parameter can be passed to the driver which will
 36 be used to calculate the CRC and pass back an appropriate slave ID to the W1
 37 core.
 38 
 39 By default the master driver and the BQ slave i/f
 40 driver(drivers/w1/slaves/w1_bq27000.c) sets the ID to 1.
 41 Please note to load both the modules with a different ID if required, but note
 42 that the ID used should be same for both master and slave driver loading.
 43 
 44 e.g::
 45 
 46   insmod omap_hdq.ko W1_ID=2
 47   insmod w1_bq27000.ko F_ID=2
 48 
 49 The driver also supports 1-wire mode. In this mode, there is no need to
 50 pass slave ID as parameter. The driver will auto-detect slaves connected
 51 to the bus using SEARCH_ROM procedure. 1-wire mode can be selected by
 52 setting "ti,mode" property to "1w" in DT (see
 53 Documentation/devicetree/bindings/w1/omap-hdq.txt for more details).
 54 By default driver is in HDQ mode.

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