Add an example to read VBUS and VSYS (#331)

The process is different on Pico and Pico W so demonstrate how to do it.

Fixes #324

README.md

@@ -23,6 +23,7 @@ App|Description
 [onboard_temperature](adc/onboard_temperature) | Display the value of the onboard temperature sensor.
 [microphone_adc](adc/microphone_adc) | Read analog values from a microphone and plot the measured sound amplitude.
 [dma_capture](adc/dma_capture) | Use the DMA to capture many samples from the ADC.
+[read_vsys](adc/read_vsys) | Demonstrates how to read VSYS to get the voltage of the power supply.
 
 ### Clocks
 

adc/CMakeLists.txt

@@ -5,4 +5,5 @@ if (NOT PICO_NO_HARDWARE)
     add_subdirectory(joystick_display)
     add_subdirectory(onboard_temperature)
     add_subdirectory(microphone_adc)
+    add_subdirectory(read_vsys)
 endif ()

adc/read_vsys/CMakeLists.txt

@@ -0,0 +1,30 @@
+add_library(power_status_adc INTERFACE)
+target_sources(power_status_adc INTERFACE
+        ${CMAKE_CURRENT_LIST_DIR}/power_status.c
+        )
+target_include_directories(power_status_adc INTERFACE
+        ${CMAKE_CURRENT_LIST_DIR}
+        )
+target_link_libraries(power_status_adc INTERFACE
+        hardware_adc
+        hardware_gpio
+        )
+
+add_executable(read_vsys
+    read_vsys.c
+    )
+target_include_directories(read_vsys PRIVATE
+    ${CMAKE_CURRENT_LIST_DIR}
+    )
+target_link_libraries(read_vsys
+    pico_stdlib
+    power_status_adc
+    )
+if (PICO_CYW43_SUPPORTED)
+    target_link_libraries(read_vsys
+        pico_cyw43_arch_none
+    )
+endif()
+
+pico_add_extra_outputs(read_vsys)
+example_auto_set_url(read_vsys)

adc/read_vsys/power_status.c

@@ -0,0 +1,78 @@
+/**
+ * Copyright (c) 2023 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include "stdbool.h"
+#include "hardware/adc.h"
+#include "power_status.h"
+
+#if CYW43_USES_VSYS_PIN
+#include "pico/cyw43_arch.h"
+#endif
+
+#ifndef PICO_POWER_SAMPLE_COUNT
+#define PICO_POWER_SAMPLE_COUNT 3
+#endif
+
+// Pin used for ADC 0
+#define PICO_FIRST_ADC_PIN 26
+
+int power_source(bool *battery_powered) {
+#if defined CYW43_WL_GPIO_VBUS_PIN
+    *battery_powered = !cyw43_arch_gpio_get(CYW43_WL_GPIO_VBUS_PIN);
+    return PICO_OK;
+#elif defined PICO_VBUS_GPIO_PIN
+    gpio_set_function(PICO_VBUS_GPIO_PIN, GPIO_FUNC_SIO);
+    *battery_powered = !gpio_get(PICO_VBUS_GPIO_PIN);
+    return PICO_OK;
+#else
+    return PICO_ERROR_NO_DATA;
+#endif
+}
+
+int power_voltage(float *voltage_result) {
+#ifndef PICO_VSYS_PIN
+    return PICO_ERROR_NO_DATA;
+#endif
+#if CYW43_USES_VSYS_PIN
+    cyw43_thread_enter();
+    // Make sure cyw43 is awake
+    cyw43_arch_gpio_get(CYW43_WL_GPIO_VBUS_PIN);
+#endif
+
+    // setup adc
+    adc_gpio_init(PICO_VSYS_PIN);
+    adc_select_input(PICO_VSYS_PIN - PICO_FIRST_ADC_PIN);
+ 
+    adc_fifo_setup(true, false, 0, false, false);
+    adc_run(true);
+
+#if CYW43_USES_VSYS_PIN
+    // We seem to read low values from cyw43 sometimes - this seems to fix it
+    int ignore_count = PICO_POWER_SAMPLE_COUNT;
+    while (!adc_fifo_is_empty() || ignore_count-- > 0) {
+        (void)adc_fifo_get_blocking();
+    }
+#endif
+
+    // read vsys
+    uint32_t vsys = 0;
+    for(int i = 0; i < PICO_POWER_SAMPLE_COUNT; i++) {
+        uint16_t val = adc_fifo_get_blocking();
+        vsys += val;
+    }
+
+    adc_run(false);
+    adc_fifo_drain();
+
+    vsys /= PICO_POWER_SAMPLE_COUNT;
+#if CYW43_USES_VSYS_PIN
+    cyw43_thread_exit();
+#endif
+    // Generate voltage
+    const float conversion_factor = 3.3f / (1 << 12);
+    *voltage_result = vsys * 3 * conversion_factor;
+    return PICO_OK;
+}

adc/read_vsys/power_status.h

@@ -0,0 +1,33 @@
+/**
+ * Copyright (c) 2023 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef POWER_STATUS_H
+#define POWER_STATUS_H
+
+/*!
+ * \brief Get power source
+ *
+ * Returns whether battery powered
+ * \note On Pico W must have called cyw43_arch_init
+ *
+ * \param battery_powered True if powered by battery, False if powered by USB or another means
+ * \return Zero if the battery status can be determined, an error code otherwise \see pico_error_codes
+ */
+
+int power_source(bool *battery_powered);
+
+/*!
+ * \brief Get system voltage
+ *
+ * Returns the system voltage
+ * \note Must have called adc_init
+ *
+ * \param voltage Calculated voltage
+ * \return Zero if the voltage can be determined, an error code otherwise \see pico_error_codes
+ */
+int power_voltage(float *voltage);
+
+#endif

adc/read_vsys/read_vsys.c

@@ -0,0 +1,75 @@
+/**
+ * Copyright (c) 2022 Raspberry Pi (Trading) Ltd.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <stdio.h>
+#include <pico/stdlib.h>
+#include <power_status.h>
+#include "hardware/adc.h"
+#include "pico/float.h"
+
+#if CYW43_USES_VSYS_PIN
+#include "pico/cyw43_arch.h"
+#endif
+
+int main() {
+    stdio_init_all();
+
+    adc_init();
+    adc_set_temp_sensor_enabled(true);
+
+    // Pico W uses a CYW43 pin to get VBUS so we need to initialise it
+    #if CYW43_USES_VSYS_PIN
+    if (cyw43_arch_init()) {
+        printf("failed to initialise\n");
+        return 1;
+    }
+    #endif
+
+    bool old_battery_status;
+    float old_voltage;
+    bool battery_status = true;
+    char *power_str = "UNKNOWN";
+
+    while(true) {
+        // Get battery status
+        if (power_source(&battery_status) == PICO_OK) {
+            power_str = battery_status ? "BATTERY" : "POWERED";
+        }
+
+        // Get voltage
+        float voltage = 0;
+        int voltage_return = power_voltage(&voltage);
+        voltage = floorf(voltage * 100) / 100;
+
+        // Display power if it's changed
+        if (old_battery_status != battery_status || old_voltage != voltage) {
+            char percent_buf[10] = {0};
+            if (battery_status && voltage_return == PICO_OK) {
+                const float min_battery_volts = 3.0f;
+                const float max_battery_volts = 4.2f;
+                int percent_val = ((voltage - min_battery_volts) / (max_battery_volts - min_battery_volts)) * 100;
+                snprintf(percent_buf, sizeof(percent_buf), " (%d%%)", percent_val);
+            }
+
+            // Also get the temperature
+            adc_select_input(4);
+            const float conversionFactor = 3.3f / (1 << 12);
+            float adc = (float)adc_read() * conversionFactor;
+            float tempC = 27.0f - (adc - 0.706f) / 0.001721f;
+
+            // Display power and remember old vales
+            printf("Power %s, %.2fV%s, temp %.1f DegC\n", power_str, voltage, percent_buf, tempC);
+            old_battery_status = battery_status;
+            old_voltage = voltage;
+        }
+        sleep_ms(1000);
+    }
+
+#if CYW43_USES_VSYS_PIN
+    cyw43_arch_deinit();
+#endif
+    return 0;
+}