VCC undervoltage check module

src/config/config.h

@@ -42,6 +42,14 @@ static constexpr const uint16_t buttonADCLimits[buttonCount][2] = { { 0, 50 }, {
 static constexpr const uint16_t buttonADCMaxValue = 1023; ///< used in unit tests
 static constexpr const uint8_t buttonsADCIndex = 5; ///< ADC index of buttons input
 
+// VCC measurement setup
+static constexpr const uint8_t VCCADCIndex = 30; ///< ADC index of scaled VCC input
+static constexpr const uint16_t VCCADCThreshold = 274; ///< ADC value for triggering the UV_VCC error
+/// We are measuring the bandgap voltage, Vb=1.1V.
+/// To compute the threshold value: `VAL = 1125.3 / AVCC`
+/// So for AVCC=4.1V, you get VAL=274.46
+static constexpr const uint8_t VCCADCReadCnt = 10; ///< Number of ADC reads to perform, only the last one being used
+
 // Motion and planning
 
 /// Do not plan moves equal or shorter than the requested steps

src/logic/error_codes.h

@@ -118,4 +118,6 @@ enum class ErrorCode : uint_fast16_t {
     /// Unfixable possible cause: bad or cracked solder joints on the PCB, failed shift register, failed driver.
     MMU_SOLDERING_NEEDS_ATTENTION = 0xC200,
 
+    /// MCU VCC rail undervoltage.
+    MCU_UNDERVOLTAGE_VCC = 0xC400,
 };

src/main.cpp

@@ -24,6 +24,7 @@
 #include "modules/timebase.h"
 #include "modules/motion.h"
 #include "modules/usb_cdc.h"
+#include "modules/undervoltage_check.h"
 
 #include "application.h"
 
@@ -167,6 +168,7 @@ void loop() {
     }
     hal::cpu::Step();
     mu::cdc.Step();
+    muv::uv_vcc.Step();
 
     application.Step();
 

src/modules/CMakeLists.txt

@@ -18,6 +18,7 @@ target_sources(
           serial.cpp
           speed_table.cpp
           timebase.cpp
+          undervoltage_check.cpp
           usb_cdc.cpp
           user_input.cpp
   )

src/modules/undervoltage_check.cpp

@@ -0,0 +1,26 @@
+/// @file undervoltage_check.cpp
+#include "undervoltage_check.h"
+#include "../hal/adc.h"
+#include "../logic/error_codes.h"
+#include "../panic.h"
+
+namespace modules {
+namespace undervoltage_check {
+
+Undervoltage_check uv_vcc;
+
+void Undervoltage_check::Step() {
+    uint16_t vcc_val;
+
+    // dummy reads are so that the final measurement is valid
+    for (uint8_t i = 0; i < config::VCCADCReadCnt; i++) {
+        vcc_val = hal::adc::ReadADC(config::VCCADCIndex);
+    }
+
+    if (vcc_val > config::VCCADCThreshold) {
+        Panic(ErrorCode::MCU_UNDERVOLTAGE_VCC);
+    }
+}
+
+} // namespace undervoltage_check
+} // namespace modules

src/modules/undervoltage_check.h

@@ -0,0 +1,25 @@
+/// @file undervoltage_check.h
+#pragma once
+
+#include <stdint.h>
+#include "../config/config.h"
+
+/// The modules namespace contains models of MMU's components
+namespace modules {
+namespace undervoltage_check {
+
+class Undervoltage_check {
+public:
+    inline constexpr Undervoltage_check() = default;
+
+    /// Reads the ADC, checks the value
+    void Step();
+};
+
+/// The one and only instance of Undervoltage_check in the FW
+extern Undervoltage_check uv_vcc;
+
+} // namespace undervoltage_check
+} // namespace modules
+
+namespace muv = modules::undervoltage_check;