10. PWM Operation Guide

This documentDescriptionin CV184x on the platformThrough sysfs ConfigurationandUse PWM、Pin Multiplexing withandCommand LineandUser-Space Program Example。

10.1. Preparation

1. Kernel Requirements

  • Use SDK Providekernel，andEnsureKernel Configurationinalready CONFIG_PWM （Driver Kernel Load，No need to insmod）。

2. Pin Multiplexing

PWM needThrough pinmux will GPIO PinConfigurationis PWM Function。inon the target boardExecute cvi_pinmux Commands ，PleasewithActualUseof PWM ChannelandSchematicis 。

Example：will PWM6 Pinfrom JTAG to PWM

cvi_pinmux -r JTAG_CPU_TCK
cvi_pinmux -w JTAG_CPU_TCK/PWM_6

Example：will PWM14 Pinfrom I2C to PWM

cvi_pinmux -r IIC2_SCL
cvi_pinmux -w IIC2_SCL/PWM_14

10.2. Operation Flow

UseMethod

  • in Through shell CommandsOperation sysfs Interface；

  • orinUser space/Kernel spacePrograminThroughRead/write sysfs NodeOperation PWM。

and sysfs Correspondence

  • Frequency：250 MHz。

  • Channel ：16 ， can ConfigurationPeriodandDuty Cycle。

  • Controllerand sysfs Path：

    • 3 PWM Controller， sysfs inof pwmchip0、pwmchip6、pwmchip12。

    • Schematiconof pwm0～pwm15 andController、sysfs ofCorrespondenceas follows：

      • pwm0～pwm5 → /sys/class/pwm/pwmchip0/pwm0～pwm5

      • pwm6～pwm11 → /sys/class/pwm/pwmchip6/pwm0～pwm5

      • pwm12～pwm15 → /sys/class/pwm/pwmchip12/pwm0～pwm3

    pwmchip6 of pwm0～pwm5 Schematic pwm6～pwm11，pwmchip12 of pwm0～pwm3 Schematic pwm12～pwm15。

10.3. Operation Example

10.3.1. Command-Line Operation Example

followingwith pwmchip0 of pwm1、pwmchip6 of pwm0、pwmchip12 of pwm2 as an example（ Schematiconof pwm1、pwm6、pwm14）。ActualUse Please needReplaceController andChannel number。

Steps 1：Export PWM Channel

echo 1 > /sys/class/pwm/pwmchip0/export
echo 0 > /sys/class/pwm/pwmchip6/export
echo 2 > /sys/class/pwm/pwmchip12/export

Steps 2：SettingsPeriod（Unit：nanoseconds）

echo 1000000 > /sys/class/pwm/pwmchip0/pwm1/period
echo 1000000 > /sys/class/pwm/pwmchip6/pwm0/period
echo 1000000 > /sys/class/pwm/pwmchip12/pwm2/period

Steps 3：SettingsDuty Cycle（Unit：nanoseconds）

echo 500000 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle   # 500000/1000000 = 50%
echo 300000 > /sys/class/pwm/pwmchip6/pwm0/duty_cycle
echo 500000 > /sys/class/pwm/pwmchip12/pwm2/duty_cycle

Steps 4：Enable PWM Output

Enableaftercanin Pin or 。

echo 1 > /sys/class/pwm/pwmchip0/pwm1/enable
echo 1 > /sys/class/pwm/pwmchip6/pwm0/enable
echo 1 > /sys/class/pwm/pwmchip12/pwm2/enable

Steps 5：Disable PWM Output

echo 0 > /sys/class/pwm/pwmchip0/pwm1/enable
echo 0 > /sys/class/pwm/pwmchip6/pwm0/enable
echo 0 > /sys/class/pwm/pwmchip12/pwm2/enable

Steps 6：Unexport PWM Channel

echo 1 > /sys/class/pwm/pwmchip0/unexport
echo 0 > /sys/class/pwm/pwmchip6/unexport
echo 2 > /sys/class/pwm/pwmchip12/unexport

Steps 7：View PWM ChannelStatus

followingwith pwmchip0/pwm1 as an example，canViewPeriod、Duty Cycle、EnableStatusandControllerInformation：

# View pwmchip0/pwm1 ofPeriod
cat /sys/class/pwm/pwmchip0/pwm1/period
# View pwmchip0/pwm1 ofDuty Cycle
cat /sys/class/pwm/pwmchip0/pwm1/duty_cycle
# View pwmchip0/pwm1  Enable（1=Enable，0=Disable）
cat /sys/class/pwm/pwmchip0/pwm1/enable
# View PWM Controllerof Information
cat /sys/class/pwm/pwmchip0/device/uevent

10.3.2. Maximum and Minimum Frequency Operation Example

followingDescriptionIf Configuration PWM of Frequencyand Frequency，and OperationStepsand 。

，need Frequencyof ， 。

Frequency

  • Device Support 50 MHz， Periodis 20 ns（\(1/50\,\mathrm{MHz} = 20\,\mathrm{ns}\)）。

  • is toValid ，Duty Cycle （duty_ns） must Period ， 50% Duty CycleTests。

with pwmchip0/pwm1 as an example：

echo 1 > /sys/class/pwm/pwmchip0/export
echo 20 > /sys/class/pwm/pwmchip0/pwm1/period      # Period 20 ns → Frequency 50 MHz
echo 10 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle  # 50% Duty Cycle：20 × 0.5 = 10 ns
echo 1 > /sys/class/pwm/pwmchip0/pwm1/enable

Result：OutputFrequency 50 MHz，Duty Cycle 50%，can in PinVerification。

Frequency

  • KernelinPeriodandDuty CycleUse （ns）Indicates，Period can 2147483646 ns（ ）。

  • isGenerateValid ，Duty Cycle （duty_ns） must Period ， Select 50% Duty CycleTests： \(\mathrm{duty\_ns} = \mathrm{period\_ns} \times 50\% = 2147483646 \times 0.5 = 1073741823\,\mathrm{ns}\)。

with pwmchip0/pwm1 as an example：

echo 1 > /sys/class/pwm/pwmchip0/export
echo 2147483646 > /sys/class/pwm/pwmchip0/pwm1/period     # Period 2147483646 ns
echo 1073741823 > /sys/class/pwm/pwmchip0/pwm1/duty_cycle # 50% Duty Cycle
echo 1 > /sys/class/pwm/pwmchip0/pwm1/enable

Result：OutputPeriod 2.147 s（Frequency 0.466 Hz），Duty Cycle 50%。can Period 。

10.3.3. User-Space Program Example

followingwith pwmchip6 of pwm0 as an example（ Schematic pwm6）， inUser spaceThrough open/write Operation sysfs CompleteExport、SettingsPeriodandDuty Cycle、Enable/DisableOutput、Unexport。PathandChannel numbercanThroughMacro PWM_PATH、PWM_NUM Modify。

： sysfs NodeWrite 

#define PWM_PATH "/sys/class/pwm/pwmchip6"
#define PWM_NUM  0

int pwm_write(const char *path, const char *value) {
    int fd = open(path, O_WRONLY);
    if (fd < 0) {
        perror("EnableFileFailure");
        return -1;
    }
    if (write(fd, value, strlen(value)) < 0) {
        perror("WriteFailure");
        close(fd);
        return -1;
    }
    close(fd);
    return 0;
}

Steps 1：Export PWM Channel

char path[256];
snprintf(path, sizeof(path), "%s/export", PWM_PATH);
if (pwm_write(path, "1") < 0)   /* Export pwm0 */
    return -1;
usleep(100000);   /* Wait  100ms  Operation Channel */

Steps 2：ConfigurationPeriod（Unit：nanoseconds，Example 1000000 ns）

snprintf(path, sizeof(path), "%s/pwm%d/period", PWM_PATH, PWM_NUM);
if (pwm_write(path, "1000000") < 0)
    return -1;

Steps 3：ConfigurationDuty Cycle（Unit：nanoseconds，Example 300000 ns）

snprintf(path, sizeof(path), "%s/pwm%d/duty_cycle", PWM_PATH, PWM_NUM);
if (pwm_write(path, "300000") < 0)
    return -1;

Steps 4：Enable PWM Output

snprintf(path, sizeof(path), "%s/pwm%d/enable", PWM_PATH, PWM_NUM);
if (pwm_write(path, "1") < 0)
    return -1;

Steps 5：Run afterDisable PWM Output

sleep(10);   /* Output 10 seconds */
if (pwm_write(path, "0") < 0)   /* path  is enable Node */
    return -1;

Steps 6：Unexport PWM Channel

snprintf(path, sizeof(path), "%s/unexport", PWM_PATH);
pwm_write(path, "1");   /* Unexport pwm0，ReturnValuecan need  */

CompleteUser spaceProgram（ Code）

willon Steps ，and on Fileand main， can tocan BuildRunofProgram：

 1// pwm_control.c
 2#include <stdio.h>
 3#include <stdlib.h>
 4#include <string.h>
 5#include <fcntl.h>
 6#include <unistd.h>
 7#include <errno.h>
 8
 9#define PWM_PATH "/sys/class/pwm/pwmchip6"
10#define PWM_NUM  0
11
12int pwm_write(const char *path, const char *value) {
13    int fd, ret;
14
15    fd = open(path, O_WRONLY);
16    if (fd < 0) {
17        perror("EnableFileFailure");
18        return -1;
19    }
20
21    ret = write(fd, value, strlen(value));
22    if (ret < 0) {
23        perror("WriteFailure");
24        close(fd);
25        return -1;
26    }
27
28    close(fd);
29    return 0;
30}
31
32int main(void) {
33    char path[256];
34    int ret;
35
36    printf("=== PWM Program ===\n");
37
38    /* 1. Export PWM Channel */
39    printf("1. ExportPWMChannel pwm%d...\n", PWM_NUM);
40    snprintf(path, sizeof(path), "%s/export", PWM_PATH);
41    ret = pwm_write(path, "1");
42    if (ret < 0) return -1;
43    printf("ExportSuccess\n");
44    usleep(100000);
45
46    /* 2. SettingsPeriod（1 kHz） */
47    printf("2. SettingsPeriodis1kHz...\n");
48    snprintf(path, sizeof(path), "%s/pwm%d/period", PWM_PATH, PWM_NUM);
49    ret = pwm_write(path, "1000000");
50    if (ret < 0) return -1;
51    printf("PeriodSettingsSuccess\n");
52
53    /* 3. SettingsDuty Cycle（30%%） */
54    printf("3. SettingsDuty Cycleis30%%...\n");
55    snprintf(path, sizeof(path), "%s/pwm%d/duty_cycle", PWM_PATH, PWM_NUM);
56    ret = pwm_write(path, "300000");
57    if (ret < 0) return -1;
58    printf("Duty CycleSettingsSuccess\n");
59
60    /* 4.   PWM */
61    printf("4.  PWMOutput...\n");
62    snprintf(path, sizeof(path), "%s/pwm%d/enable", PWM_PATH, PWM_NUM);
63    ret = pwm_write(path, "1");
64    if (ret < 0) return -1;
65    printf("PWMalready \n");
66
67    /* 5. Run 10 seconds */
68    printf("PWMOutputin，10seconds laterDisable...\n");
69    sleep(10);
70
71    /* 6. Disable PWM */
72    printf("5. DisablePWM...\n");
73    ret = pwm_write(path, "0");
74    if (ret < 0) return -1;
75    printf("PWMalreadyDisable\n");
76
77    /* 7. Unexport（Optional） */
78    printf("6. UnexportPWMChannel...\n");
79    snprintf(path, sizeof(path), "%s/unexport", PWM_PATH);
80    pwm_write(path, "1");
81    printf("PWMChannelalreadyUnexport\n");
82
83    return 0;
84}

10.3.4. Run Mode Description

  1. Source Code：willon CompleteUser spaceProgram isFile，for example pwm_control.c。

  2. Build：inHostoron the target boardUse Tools Build。Example（ is ARM PleaseReplaceisActual Build ）：

    #  BuildExample（withActualTools is ）
arm-none-linux-uclibcgnueabihf-gcc -o pwm_control pwm_control.c -static

  3. Run：willcanExecuteFileCopyto after，inon the target boardExecute。need /sys/class/pwm （ need root or ）。

    ./pwm_control

    Programwill ：Export pwmchip6 of pwm0、Settings 1 kHz Periodand 30%% Duty Cycle、 PWM Output、Run 10 seconds、DisableOutput、Unexport。canin Pin 。

  4. ModifyChannelandPath：IfUse ControllerorChannel，PleaseModifySource Codeinof PWM_PATH（If /sys/class/pwm/pwmchip0）、PWM_NUM（If 1），withand export/unexport inWriteofChannel number， and 「 and sysfs Correspondence」 。