User manual

UDOO Starting manual (beta) Version 0.3
http://www.udoo.org/
31"
6. i.MX6 Pinmuxing
6.1. Introduction
i.MX6 processor provides a dedicated controller for pin-muxing options, named
IOMUX Controller(IOMUXC). The IOMUX Controller allows to the IC to share one pad
between several functional blocks. The sharing is done by multiplexing the pad
input/output signals.
Every module requires a specific pad setting (such as pull up, keeper, and so on),
and for each signal, there are up to 8 muxing options (called ALT modes). The pad
settings parameters are controlled by the IOMUXC.
In the Linux kernel, it is necessary to define a specific file for each platform. For
UDOO, it can be found in:
<KERNEL_ROOT>/arch/arm/mach_mx6/board_mx6_seco_UDOO.c
This file contains specific drivers initializations, like ethernet, hdmi, sd, and so on..
At the beginningof the function __init mx6_seco_UDOO_board_init(void), there is
the following code:
if (cpu_is_mx6q () ) {
mxc_iomux_v3_setup_multiple_pads (mx6qd_seco_UDOO_pads,
ARRAY_SIZE (mx6qd_seco_UDOO_pads) );
printk ( "\n>UDOO quad" ) ;
}
else if ( cpu_is_mx6dl () ) {
mxc_iomux_v3_setup_multiple_pads (mx6sdl_seco_UDOO_pads,
ARRAY_SIZE (mx6sdl_seco_UDOO_pads) );
printk ( "\n>UDOO dual " ) ;
}
It recognizes the UDOO version used, and load the necessary macros needed for it.
mx6qd_seco_UDOO_pads and mx6sdl_seco_UDOO_pads are two array of macros
defined in two header files, one for each processor type. Both .h files are included in
the .c file.
<KERNEL_ROOT>/arch/arm/mach_mx6/board_mx6qd_seco_UDOO.h (QUAD)
<KERNEL_ROOT>/arch/arm/mach_mx6/board_mx6sdl_seco_UDOO.h (DUAL)
mxc_iomux_v3_setup_multiple_pads reads the macros and set the correct bits
values in registers.
Each header file defines:
● custom macros for some pins
● GPIOs id number (i.MX6 pins are divided in banks and identified by id. To
make them visible by the OS it is necessary to give them a single id number.
IMX_GIPO_NR provide this function).
● macro’ s array used for pinmuxing
● an array containing the pins set as GPIOs that must be configured in output
mode with high value