Add VEML6075 scaffolding.

Also, remove DHT dependency and add a note in mos.yml to have
application owners include those libraries. Without them, we'll compile
no scaffolding. With them, we'll pull those in based on -DHAVE_* macros.

mos.yml

@@ -18,13 +18,17 @@ config_schema:
   - ["sensors", "o", {title: "Sensors settings"}]
   - ["sensors.dht_gpio", "s", "13,12,14", {title: "Comma Separated list of GPIO pins to enable DHT22/AM2302 sensors on"}]
   - ["sensors.dht_period", "i", 3, {title: "Sample period in seconds for DHT sensors"}]
+  - ["sensors.veml6075_i2caddr", "i", 0x10, {title: "I2C Address for VEML6075 sensor"}]
+  - ["sensors.veml6075_period", "i", 3, {title: "Sample period in seconds for VEML6075 sensor"}]
   - ["sensors.pushgateway_period", "i", 10, {title: "Period in seconds for Prometheus Pushgateway POSTs"}]
   - ["prometheus.pushgateway", "prometheus.example.net:9091"]
 
 
 # List of libraries used by this app, in order of initialisation
+# Note: To use sensor libraries, include one or more of these in your application mos.yml:
+#  - origin: https://github.com/mongoose-os-libs/dht
+#  - origin: https://github.com/mongoose-os-libs/veml6075-i2c
 libs:
-  - origin: https://github.com/mongoose-os-libs/dht
   - origin: https://github.com/mongoose-os-libs/prometheus-metrics
 
 # Used by the mos tool to catch mos binaries incompatible with this file format

src/mgos_prometheus_sensors.c

@@ -3,6 +3,7 @@
 #include "mgos_prometheus_sensors.h"
 
 void dht_init();
+void veml6075_init();
 
 static void pushgateway_timer(void *user_data) {
   mgos_prometheus_metrics_push(MGOS_APP, mgos_sys_config_get_device_id());
@@ -11,6 +12,7 @@ static void pushgateway_timer(void *user_data) {
 
 bool mgos_prometheus_sensors_init(void) {
   dht_init();
+  veml6075_init();
   if (mgos_sys_config_get_sensors_pushgateway_period()>0)
     mgos_set_timer(mgos_sys_config_get_sensors_pushgateway_period()*1000, true, pushgateway_timer, NULL);
   return true;

src/veml6075.c

@@ -0,0 +1,67 @@
+#include "mgos.h"
+
+#ifdef MGOS_HAVE_VEML6075_I2C
+#include "mgos_veml6075.h"
+#include "mgos_config.h"
+#include "mgos_prometheus_metrics.h"
+#include "mgos_prometheus_sensors.h"
+
+static struct mgos_veml6075 *s_veml6075;
+
+static void print_chunk(struct mg_connection *nc, char *name, char *fmt, ...) {
+  char chunk[500];
+  int chunklen=0;
+  va_list ap;
+
+  snprintf(chunk, sizeof(chunk), "%s%s", name, fmt[0]=='{' ? "" : " ");
+  va_start(ap, fmt);
+  vsnprintf(chunk+strlen(chunk), sizeof(chunk)-strlen(chunk), fmt, ap);
+  va_end(ap);
+  strncat(chunk, "\n", sizeof(chunk));
+  chunklen=strlen(chunk);
+//  LOG(LL_DEBUG, ("Chunk '%s' with length %d", chunk, chunklen));
+  mg_printf(nc, "%X\r\n%s\r\n", chunklen, chunk);
+}
+
+static void veml6075_prometheus_metrics(struct mg_connection *nc, void *user_data) {
+  // BUG -- repeated HELP and TYPE makes Prometheus parser bork :(
+  mgos_prometheus_metrics_printf(nc, GAUGE,
+    "UV", "Ultra Violet light intensity, in sensor counts",
+    "{band=\"UVA\",type=\"VEML6075\", sensor=\"0\"} %f", mgos_veml6075_getUVA(s_veml6075));
+  print_chunk(nc, "UV", "{band=\"UVB\",type=\"VEML6075\", sensor=\"0\"} %f", mgos_veml6075_getUVB(s_veml6075));
+
+  mgos_prometheus_metrics_printf(nc, GAUGE,
+    "UVIndex", "2: Low, 5.5 Moderate, 7.5 High, 10.5 Very High, else Extreme",
+    "{sensor=\"0\",type=\"VEML6075\"} %f", mgos_veml6075_getUVIndex(s_veml6075));
+
+  (void) user_data;
+}
+
+static void veml6075_timer_cb(void *user_data) {
+  double start;
+  uint32_t usecs=0;
+  float uva, uvb, uvindex;
+
+  start=mgos_uptime();
+  uva=mgos_veml6075_getUVA(s_veml6075);
+  uvb=mgos_veml6075_getUVB(s_veml6075);
+  uvindex=mgos_veml6075_getUVIndex(s_veml6075);
+  usecs=1000000*(mgos_uptime()-start);
+  LOG(LL_INFO, ("VEML6075 sensor=0 uva=%.1f uvb=%.1f uvindex=%.2f usecs=%u", uva, uvb, uvindex, usecs));
+
+  (void) user_data;
+}
+
+void veml6075_init() {
+  s_veml6075 = mgos_veml6075_create(mgos_sys_config_get_sensors_veml6075_i2caddr());
+  if (s_veml6075) {
+    mgos_set_timer(mgos_sys_config_get_sensors_veml6075_period()*1000, true, veml6075_timer_cb, NULL);
+    mgos_prometheus_metrics_add_handler(veml6075_prometheus_metrics, NULL);
+  }
+}
+
+#else
+void veml6075_init() {
+  LOG(LL_ERROR, ("VEML6075 disabled, include library in mos.yml to enable"));
+}
+#endif