OMAP Capture driver

This driver can set up a pin on the OMAP 35xx processor as an input capture source. The original purpose was to measure the frequency of a signal that corresponded to the RPM of a motor. Only 4 pins on the 35XX can be used for capture: 144, 145, 146 and 147. The driver assumes that the capture pin is in "Mode 2" (pwm_evt). The driver default is to set up pin 147 for capture. To set up one of the other pins as capture, invoke the driver with "capture_pin=xxx", where "xxx" is one of 144, 145, 146 and 147. Pulse width (rising edge to falling edge) and frequency measurements can be made on a signal connected to the capture pin. The driver continuously captures width and frequency counts. If there is no input on the pin, or the input goes away, the driver will report 0 for pulse width and frequency counts. The ioctl interface will provide an integer count for pulse width, frequency and clock source. To determine the values in milliseconds, divide the returned count of width or frequency by the clock source count and multiply by 1000.

Compiling: make V=1 -f Makefile ARCH=arm KERNELDIR=/home/fagius/git/sakoman/linux-omap-2.6_head RCH=arm CROSS_COMPILE=/usr/local/angstrom/arm/bin/arm-angstrom-linux-gnueabi-

Installing:

insmod omap_capture.ko capture_pin=146

Testing:

The following c code can be used to access driver data:

/ Test code for the omap capture driver

• Copyright (C) 2010 iRobot Corporation
• Frank Agius [email protected]
• This program is free software; you can redistribute it and/or
• modify it under the terms of the GNU General Public License
• version 2 as published by the Free Software Foundation.
• 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.
• 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., 51 Franklin St, Fifth Floor, Boston, MA
• 02110-1301 USA

• */

include <sys/ioctl.h>

include <sys/types.h>

include <sys/stat.h>

include

include

include

include

include

include

include

typedef uint8_t u8; typedef uint16_t u16;

define CAPTURE_IOC_MAGIC ';'

define CAPTURE_IOCX_READ _IO(CAPTURE_IOC_MAGIC, 0)

struct omap_capture_user_parms { int channel; int average; int status; unsigned long clock; unsigned long pulse_width; unsigned long frequency; };

int main(int argc, char *argv) { int j; int d = open("/dev/omap-capture", O_RDWR | O_NONBLOCK); int ret; float pulse_width,frequency; struct omap_capture_user_parms par;

if (d == -1) { printf("could not open capture device "); return 1; }

par = malloc(sizeof(struct omap_capture_user_parms));

// read capture info ret = ioctl(d, CAPTURE_IOCX_READ, par);

pulse_width = ((float)par->pulse_width / (float)par->clock) 1000 1000; frequency = ((float)par->frequency / (float)par->clock) 1000 1000;

printf("pulse_width = %0.3f us frequency = %0.3f us ",pulse_width,frequency);

return 0; }