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author | ian <ian@FreeBSD.org> | 2014-11-21 21:30:08 +0000 |
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committer | ian <ian@FreeBSD.org> | 2014-11-21 21:30:08 +0000 |
commit | 019421f910519efbd5c4dde1d183a65fd13284bf (patch) | |
tree | b8ba1e4286a6e512dff2869336662bd166b5d55f /share/man/man4/iicbus.4 | |
parent | 54cb61b939db12c5e59cca001a7b4f06337d1fd0 (diff) | |
download | FreeBSD-src-019421f910519efbd5c4dde1d183a65fd13284bf.zip FreeBSD-src-019421f910519efbd5c4dde1d183a65fd13284bf.tar.gz |
Document the recent enhancements for configuring bus speed in iicbus(4).
Differential Revision: https://reviews.freebsd.org/D1182
PR: 195009
Diffstat (limited to 'share/man/man4/iicbus.4')
-rw-r--r-- | share/man/man4/iicbus.4 | 51 |
1 files changed, 49 insertions, 2 deletions
diff --git a/share/man/man4/iicbus.4 b/share/man/man4/iicbus.4 index 4bbc846..ce9d586 100644 --- a/share/man/man4/iicbus.4 +++ b/share/man/man4/iicbus.4 @@ -24,7 +24,7 @@ .\" .\" $FreeBSD$ .\" -.Dd June 24, 2014 +.Dd November 17, 2014 .Dt IICBUS 4 .Os .Sh NAME @@ -103,12 +103,59 @@ Some I2C interfaces are available: .It Sy lpbb Ta "parallel port specific bit-banging interface" .It Sy bktr Ta "Brooktree848 video chipset, hardware and software master-only interface" .El +.Sh BUS FREQUENCY CONFIGURATION +The operating frequency of an I2C bus may be fixed or configurable. +The bus may be used as part of some larger standard interface, and that +interface specification may require a fixed frequency. +The driver for that hardware would not honor an attempt to configure a +different speed. +A general purpose I2C bus, such as those found in many embedded systems, +will often support multiple bus frequencies. +.Pp +When a system supports multiple I2C busses, a different frequency can +be configured for each bus by number, represented by the +.Va %d +in the variable names below. +Busses can be configured using any combination of device hints, +Flattened Device Tree (FDT) data, tunables set via +.Xr loader 8 , +or at runtime using +.Xr sysctl 8 . +When configuration is supplied using more than one method, FDT and +hint data will be overridden by a tunable, which can be overriden by +.Xr sysctl 8 . +.Ss Device Hints +Set +.Va hint.iicbus.%d.frequency +to the frequency in Hz, on systems that use device hints to configure +I2C devices. +The hint is also honored by systems that use FDT data if +no frequency is configured using FDT. +.Ss Flattened Device Tree Data +Configure the I2C bus speed using the FDT standard +.Va clock-frequency +property of the node describing the I2C controller hardware. +.Ss Sysctl and Tunable +Set +.Va dev.iicbus.%d.frequency +in +.Xr loader.conf 5 . +The same variable can be changed at any time with +.Xr sysctl 8 . +Reset the bus using +.Xr i2c 8 +or the +.Xr iic 4 +.Va I2CRSTCARD +ioctl to make the change take effect. .Sh SEE ALSO .Xr bktr 4 , +.Xr fdt 4 , .Xr iic 4 , .Xr iicbb 4 , .Xr lpbb 4 , -.Xr pcf 4 +.Xr pcf 4 , +.Xr i2c 8 .Sh HISTORY The .Nm |