[FAQ11102]MT6571使用PWM配置背光如何配置，及频率计算

MT6571 使用PWM配置背光及频率计算

 

 

[SOLUTION]

 

以GPIO52 pin为例：

Mode0	Mode1	Mode2	Mode3
GPIO52	LPD8	PWM_BL	PWM_A

 

一、将GPIO52在DCT tool配置成PWM1，用于背光。

static struct cust_mt65xx_led cust_led_list[MT65XX_LED_TYPE_TOTAL] = {

                {"red",               MT65XX_LED_MODE_NONE, -1,{0}},

                {"green",             MT65XX_LED_MODE_NONE, -1,{0}},

                {"blue",              MT65XX_LED_MODE_NONE, -1,{0}},

                {"jogball-backlight", MT65XX_LED_MODE_NONE, -1,{0}},

                {"keyboard-backlight",MT65XX_LED_MODE_NONE, -1,{0}},

                {"button-backlight",  MT65XX_LED_MODE_NONE, -1,{0,0,0,0,0}},

                {"lcd-backlight",     MT65XX_LED_MODE_PWM, PWM1, {0,0,0,0,0}},

};

 1. PWM config data结构体解析

   clock_source: clock source frequency, can be 0/1

   div: clock division, can be any value within 0~7 (i.e. 1/2^(div) = /1, /2, /4, /8, /16, /32, /64, /128)

   low_duration: only for BACKLIGHT_LEVEL_PWM_64_FIFO_MODE_SUPPORT

   High_duration: only for BACKLIGHT_LEVEL_PWM_64_FIFO_MODE_SUPPORT

 2. PWM频率计算：

  If BACKLIGHT_LEVEL_PWM_MODE_CONFIG = BACKLIGHT_LEVEL_PWM_256_SUPPORT,

             PWM freq. = clock source / 2^(div) / 256 

  If BACKLIGHT_LEVEL_PWM_MODE_CONFIG = BACKLIGHT_LEVEL_PWM_64_FIFO_MODE_SUPPORT,

             PWM freq. = clock source / 2^(div) / [(High_duration+1)(Level')+(low_duration+1)(64 - Level')]

                        = clock source / 2^(div) / [(High_duration+1)*64]     (when low_duration = High_duration)

 时钟源:

             0: block clock/1625 = 26M/1625 = 16K (MT6571)

             1: block clock = 26M (MT6571)

 Div: 0~7

 例如, in MT6571, PWM_config = {1,1,0,0,0}

             ==> PWM freq. = 26M/2^1/256                 =            50.78 KHz ( when BACKLIGHT_LEVEL_PWM_256_SUPPORT )

             ==> PWM freq. = 26M/2^1/(0+1)*64 = 203.13 KHz ( when BACKLIGHT_LEVEL_PWM_64_FIFO_MODE_SUPPORT )

二、将GPIO52在DCT Tool配置成PWM_BL.

 static struct cust_mt65xx_led cust_led_list[MT65XX_LED_TYPE_TOTAL] = {

                {"red",               MT65XX_LED_MODE_NONE, -1,{0}},

                {"green",             MT65XX_LED_MODE_NONE, -1,{0}},

                {"blue",              MT65XX_LED_MODE_NONE, -1,{0}},

                {"jogball-backlight", MT65XX_LED_MODE_NONE, -1,{0}},

                {"keyboard-backlight",MT65XX_LED_MODE_NONE, -1,{0}},

                {"button-backlight",  MT65XX_LED_MODE_NONE, -1,{0,0,0,0,0}},

                {"lcd-backlight",     MT65XX_LED_MODE_CUST_BLS_PWM, (int)disp_bls_set_backlight, {0,0,0,0,0}},

};

1. PWM config data结构体解析

             clock_source: clock source frequency, can be 0/1/2/3

             div: clock division, can be any value within 0~1023

             low_duration: non-use

             High_duration: non-use

             pmic_pad: non-use

 

 2. 频率计算

PWM freq.= clock source / (div + 1) /1024

Clock source:

             0: 26 MHz

             1: 104 MHz

Div: 0~1023

 By default, clock_source = 0 and div = 0 => PWM freq. = 26 KHz

波形图如下：