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aod: PPI/RTC-based backlight brightness
1 parent 3f08155 commit 5bfae21

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4 files changed

+146
-16
lines changed

4 files changed

+146
-16
lines changed

‎src/components/brightness/BrightnessController.cpp

+112-12
Original file line numberDiff line numberDiff line change
@@ -2,38 +2,138 @@
22
#include <hal/nrf_gpio.h>
33
#include "displayapp/screens/Symbols.h"
44
#include "drivers/PinMap.h"
5+
#include <libraries/delay/nrf_delay.h>
56
using namespace Pinetime::Controllers;
67

8+
namespace {
9+
// reinterpret_cast is not constexpr so this is the best we can do
10+
static NRF_RTC_Type* const RTC = reinterpret_cast<NRF_RTC_Type*>(NRF_RTC2_BASE);
11+
}
12+
713
void BrightnessController::Init() {
814
nrf_gpio_cfg_output(PinMap::LcdBacklightLow);
915
nrf_gpio_cfg_output(PinMap::LcdBacklightMedium);
1016
nrf_gpio_cfg_output(PinMap::LcdBacklightHigh);
17+
18+
nrf_gpio_pin_clear(PinMap::LcdBacklightLow);
19+
nrf_gpio_pin_clear(PinMap::LcdBacklightMedium);
20+
nrf_gpio_pin_clear(PinMap::LcdBacklightHigh);
21+
22+
static_assert(timerFrequency == 32768, "Change the prescaler below");
23+
RTC->PRESCALER = 0;
24+
// CC1 switches the backlight on (pin transitions from high to low) and resets the counter to 0
25+
RTC->CC[1] = timerPeriod;
26+
// Enable compare events for CC0,CC1
27+
RTC->EVTEN = 0b0000'0000'0000'0011'0000'0000'0000'0000;
28+
// Disable all interrupts
29+
RTC->INTENCLR = 0b0000'0000'0000'1111'0000'0000'0000'0011;
1130
Set(level);
1231
}
1332

33+
void BrightnessController::ApplyBrightness(uint16_t rawBrightness) {
34+
// The classic off, low, medium, high brightnesses are at {0, timerPeriod, timerPeriod*2, timerPeriod*3}
35+
// These brightness levels do not use PWM: they only set/clear the corresponding pins
36+
// Any brightness level between the above levels is achieved with efficient RTC based PWM on the next pin up
37+
// E.g 2.5*timerPeriod corresponds to medium brightness with 50% PWM on the high pin
38+
// Note: Raw brightness does not necessarily correspond to a linear perceived brightness
39+
40+
uint8_t pin;
41+
if (rawBrightness > 2 * timerPeriod) {
42+
rawBrightness -= 2 * timerPeriod;
43+
pin = PinMap::LcdBacklightHigh;
44+
} else if (rawBrightness > timerPeriod) {
45+
rawBrightness -= timerPeriod;
46+
pin = PinMap::LcdBacklightMedium;
47+
} else {
48+
pin = PinMap::LcdBacklightLow;
49+
}
50+
if (rawBrightness == timerPeriod || rawBrightness == 0) {
51+
if (lastPin != UNSET) {
52+
RTC->TASKS_STOP = 1;
53+
nrf_delay_us(rtcStopTime);
54+
nrf_ppi_channel_disable(ppiBacklightOff);
55+
nrf_ppi_channel_disable(ppiBacklightOn);
56+
nrfx_gpiote_out_uninit(lastPin);
57+
nrf_gpio_cfg_output(lastPin);
58+
}
59+
lastPin = UNSET;
60+
if (rawBrightness == 0) {
61+
nrf_gpio_pin_set(pin);
62+
} else {
63+
nrf_gpio_pin_clear(pin);
64+
}
65+
} else {
66+
// If the pin on which we are doing PWM is changing
67+
// Disable old PWM channel (if exists) and set up new one
68+
if (lastPin != pin) {
69+
if (lastPin != UNSET) {
70+
RTC->TASKS_STOP = 1;
71+
nrf_delay_us(rtcStopTime);
72+
nrf_ppi_channel_disable(ppiBacklightOff);
73+
nrf_ppi_channel_disable(ppiBacklightOn);
74+
nrfx_gpiote_out_uninit(lastPin);
75+
nrf_gpio_cfg_output(lastPin);
76+
}
77+
nrfx_gpiote_out_config_t gpioteCfg = {.action = NRF_GPIOTE_POLARITY_TOGGLE,
78+
.init_state = NRF_GPIOTE_INITIAL_VALUE_LOW,
79+
.task_pin = true};
80+
APP_ERROR_CHECK(nrfx_gpiote_out_init(pin, &gpioteCfg));
81+
nrfx_gpiote_out_task_enable(pin);
82+
nrf_ppi_channel_endpoint_setup(ppiBacklightOff,
83+
reinterpret_cast<uint32_t>(&RTC->EVENTS_COMPARE[0]),
84+
nrfx_gpiote_out_task_addr_get(pin));
85+
nrf_ppi_channel_endpoint_setup(ppiBacklightOn,
86+
reinterpret_cast<uint32_t>(&RTC->EVENTS_COMPARE[1]),
87+
nrfx_gpiote_out_task_addr_get(pin));
88+
nrf_ppi_fork_endpoint_setup(ppiBacklightOn, reinterpret_cast<uint32_t>(&RTC->TASKS_CLEAR));
89+
nrf_ppi_channel_enable(ppiBacklightOff);
90+
nrf_ppi_channel_enable(ppiBacklightOn);
91+
} else {
92+
// If the pin used for PWM isn't changing, we only need to set the pin state to the initial value (low)
93+
RTC->TASKS_STOP = 1;
94+
nrf_delay_us(rtcStopTime);
95+
// Due to errata 20,179 and the intricacies of RTC timing, keep it simple: override the pin state
96+
nrfx_gpiote_out_task_force(pin, false);
97+
}
98+
// CC0 switches the backlight off (pin transitions from low to high)
99+
RTC->CC[0] = rawBrightness;
100+
RTC->TASKS_CLEAR = 1;
101+
RTC->TASKS_START = 1;
102+
lastPin = pin;
103+
}
104+
switch (pin) {
105+
case PinMap::LcdBacklightHigh:
106+
nrf_gpio_pin_clear(PinMap::LcdBacklightLow);
107+
nrf_gpio_pin_clear(PinMap::LcdBacklightMedium);
108+
break;
109+
case PinMap::LcdBacklightMedium:
110+
nrf_gpio_pin_clear(PinMap::LcdBacklightLow);
111+
nrf_gpio_pin_set(PinMap::LcdBacklightHigh);
112+
break;
113+
case PinMap::LcdBacklightLow:
114+
nrf_gpio_pin_set(PinMap::LcdBacklightMedium);
115+
nrf_gpio_pin_set(PinMap::LcdBacklightHigh);
116+
}
117+
}
118+
14119
void BrightnessController::Set(BrightnessController::Levels level) {
15120
this->level = level;
16121
switch (level) {
17122
default:
18123
case Levels::High:
19-
nrf_gpio_pin_clear(PinMap::LcdBacklightLow);
20-
nrf_gpio_pin_clear(PinMap::LcdBacklightMedium);
21-
nrf_gpio_pin_clear(PinMap::LcdBacklightHigh);
124+
ApplyBrightness(3 * timerPeriod);
22125
break;
23126
case Levels::Medium:
24-
nrf_gpio_pin_clear(PinMap::LcdBacklightLow);
25-
nrf_gpio_pin_clear(PinMap::LcdBacklightMedium);
26-
nrf_gpio_pin_set(PinMap::LcdBacklightHigh);
127+
ApplyBrightness(2 * timerPeriod);
27128
break;
28129
case Levels::Low:
29-
nrf_gpio_pin_clear(PinMap::LcdBacklightLow);
30-
nrf_gpio_pin_set(PinMap::LcdBacklightMedium);
31-
nrf_gpio_pin_set(PinMap::LcdBacklightHigh);
130+
ApplyBrightness(timerPeriod);
131+
break;
132+
case Levels::AlwaysOn:
133+
ApplyBrightness(timerPeriod / 10);
32134
break;
33135
case Levels::Off:
34-
nrf_gpio_pin_set(PinMap::LcdBacklightLow);
35-
nrf_gpio_pin_set(PinMap::LcdBacklightMedium);
36-
nrf_gpio_pin_set(PinMap::LcdBacklightHigh);
136+
ApplyBrightness(0);
37137
break;
38138
}
39139
}

‎src/components/brightness/BrightnessController.h

+23-1
Original file line numberDiff line numberDiff line change
@@ -2,11 +2,14 @@
22

33
#include <cstdint>
44

5+
#include "nrf_ppi.h"
6+
#include "nrfx_gpiote.h"
7+
58
namespace Pinetime {
69
namespace Controllers {
710
class BrightnessController {
811
public:
9-
enum class Levels { Off, Low, Medium, High };
12+
enum class Levels { Off, AlwaysOn, Low, Medium, High };
1013
void Init();
1114

1215
void Set(Levels level);
@@ -20,6 +23,25 @@ namespace Pinetime {
2023

2124
private:
2225
Levels level = Levels::High;
26+
static constexpr uint8_t UNSET = UINT8_MAX;
27+
uint8_t lastPin = UNSET;
28+
// Maximum time (μs) it takes for the RTC to fully stop
29+
static constexpr uint8_t rtcStopTime = 46;
30+
// Frequency of timer used for PWM (Hz)
31+
static constexpr uint16_t timerFrequency = 32768;
32+
// Backlight PWM frequency (Hz)
33+
static constexpr uint16_t pwmFreq = 1000;
34+
// Wraparound point in timer ticks
35+
// Defines the number of brightness levels between each pin
36+
static constexpr uint16_t timerPeriod = timerFrequency / pwmFreq;
37+
// Warning: nimble reserves some PPIs
38+
// https://github.com/InfiniTimeOrg/InfiniTime/blob/034d83fe6baf1ab3875a34f8cee387e24410a824/src/libs/mynewt-nimble/nimble/drivers/nrf52/src/ble_phy.c#L53
39+
// SpiMaster uses PPI 0 for an erratum workaround
40+
// Channel 1, 2 should be free to use
41+
static constexpr nrf_ppi_channel_t ppiBacklightOn = NRF_PPI_CHANNEL1;
42+
static constexpr nrf_ppi_channel_t ppiBacklightOff = NRF_PPI_CHANNEL2;
43+
44+
void ApplyBrightness(uint16_t val);
2345
};
2446
}
2547
}

‎src/displayapp/DisplayApp.cpp

+8-2
Original file line numberDiff line numberDiff line change
@@ -242,11 +242,17 @@ void DisplayApp::Refresh() {
242242
RestoreBrightness();
243243
break;
244244
case Messages::GoToSleep:
245-
while (brightnessController.Level() != Controllers::BrightnessController::Levels::Off) {
245+
while (brightnessController.Level() != Controllers::BrightnessController::Levels::Low) {
246246
brightnessController.Lower();
247247
vTaskDelay(100);
248248
}
249-
lcd.Sleep();
249+
// Don't actually turn off the display for AlwaysOn mode
250+
if (settingsController.GetAlwaysOnDisplay()) {
251+
brightnessController.Set(Controllers::BrightnessController::Levels::AlwaysOn);
252+
} else {
253+
brightnessController.Set(Controllers::BrightnessController::Levels::Off);
254+
lcd.Sleep();
255+
}
250256
PushMessageToSystemTask(Pinetime::System::Messages::OnDisplayTaskSleeping);
251257
state = States::Idle;
252258
break;

‎src/systemtask/SystemTask.cpp

+3-1
Original file line numberDiff line numberDiff line change
@@ -102,7 +102,9 @@ void SystemTask::Work() {
102102
watchdog.Setup(7, Drivers::Watchdog::SleepBehaviour::Run, Drivers::Watchdog::HaltBehaviour::Pause);
103103
watchdog.Start();
104104
NRF_LOG_INFO("Last reset reason : %s", Pinetime::Drivers::ResetReasonToString(watchdog.GetResetReason()));
105-
APP_GPIOTE_INIT(2);
105+
if (!nrfx_gpiote_is_init()) {
106+
nrfx_gpiote_init();
107+
}
106108

107109
spi.Init();
108110
spiNorFlash.Init();

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