Continously sample ADCs and expose them via USB HID

JumperlessNano/include/custom_tusb_config.h

@@ -65,14 +65,14 @@ extern "C" {
 // Device Configuration
 //--------------------------------------------------------------------
 
-#define CFG_TUD_ENDOINT0_SIZE 64
+#define CFG_TUD_ENDOINT0_SIZE 256
 
 #define CFG_TUD_CDC 2
 
-#define CFG_TUD_MSC 1
+#define CFG_TUD_MSC 0
 #define CFG_TUD_HID 1
-#define CFG_TUD_MIDI 1
+#define CFG_TUD_MIDI 0
-#define CFG_TUD_VENDOR 1
+#define CFG_TUD_VENDOR 0
 
 // CDC FIFO size of TX and RX
 #define CFG_TUD_CDC_RX_BUFSIZE 256

JumperlessNano/src/AdcHid.cpp

@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: MIT
+
+#ifdef USE_TINYUSB
+#include <Adafruit_TinyUSB.h>
+#endif
+
+#ifdef CFG_TUSB_CONFIG_FILE
+#include CFG_TUSB_CONFIG_FILE
+#else
+#include "tusb_config.h"
+#endif
+
+#include <ADCInput.h>
+
+// Other parts of the code can just read from here instead of using `analogRead`
+volatile uint16_t adcReadings[4] = { 0, 0, 0, 0 };
+
+Adafruit_USBD_HID USBHID;
+
+uint8_t desc_hid_report[] = {
+  TUD_HID_REPORT_DESC_GENERIC_INOUT(sizeof(adcReadings))
+};
+
+// samples all four pins, round-robin
+ADCInput adc(A0, A1, A2, A3);
+
+static uint16_t getReportCallback(uint8_t report_id, hid_report_type_t report_type,
+                             uint8_t *buffer, uint16_t reqlen) {
+  // ignore this.
+  return 0;
+}
+
+static void setReportCallback(uint8_t report_id, hid_report_type_t report_type, uint8_t const* buffer, uint16_t bufsize)
+{
+  // ignore this as well.
+}
+
+// called when the ADC buffer has data
+static void adcCallback() {
+  if (adc.available() < 4) {
+    return;
+  }
+  // need a separate buffer here, since `sendReport` can't accept a volatile buffer.
+  uint16_t buf[4];
+  buf[0] = adcReadings[0] = adc.read();
+  buf[1] = adcReadings[1] = adc.read();
+  buf[2] = adcReadings[2] = adc.read();
+  buf[3] = adcReadings[3] = adc.read();
+
+  // only send readings if HID is "ready". Otherwise `sendReport` just hangs.
+  if (tud_hid_n_ready(0)) {
+    USBHID.sendReport(0, buf, sizeof(buf));
+  }
+}
+
+void setupAdcHidStuff() {
+  USBHID.setPollInterval(1);
+  USBHID.setReportDescriptor(desc_hid_report, sizeof(desc_hid_report));
+  USBHID.setStringDescriptor("Jumperless USB Analog");
+  USBHID.setReportCallback(getReportCallback, setReportCallback);
+  USBHID.begin();
+
+  adc.setBuffers(4, 32);
+  adc.onReceive(adcCallback);
+  // the sample rate passed here is already adjusted for the number of pins.
+  // in other words: passing 1000 actually samples at a rate of 4000, such that
+  // values for all 4 pins are available every millisecond.
+  adc.begin(1000);
+}

JumperlessNano/src/AdcHid.h

@@ -0,0 +1,11 @@
+// SPDX-License-Identifier: MIT
+
+#ifndef JUMPERLESS_HID_H
+#define JUMPERLESS_HID_H
+
+// if `setupAdcHidStuff` was called, this always contains somewhat up-to-date ADC readings
+extern uint16_t adcReadings[4];
+
+void setupAdcHidStuff();
+
+#endif

JumperlessNano/src/main.cpp

@@ -45,6 +45,8 @@
 
 #endif
 
+#include "AdcHid.h"
+
 Adafruit_USBD_CDC USBSer1;
 
 int supplySwitchPosition = 0;
@@ -77,13 +79,15 @@ void setup()
 
   USBSer1.begin(115200);
 
+  setupAdcHidStuff();
+
 #ifdef EEPROMSTUFF
   EEPROM.begin(256);
   debugFlagInit();
 
 #endif
 
-  initADC();
+  //initADC();
   delay(1);
   initDAC(); // also sets revisionNumber
   delay(1);