MT6571 使用PWM配置背光及频率计算

[DESCRIPTION]
MT6571 使用PWM配置背光及频率计算
[SOLUTION]
以GPIO52 pin为例：

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)
Mode0 Mode1 Mode2 Mode3
GPIO52 LPD8 PWM_BL PWM_A
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 )
波形图如下：

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：

更加具体的信息请参考DCC文档：
MT6571_Backlight_Config_SOP