Merge positioning API (#264)

This merge commit adds the positioning API, including the following elements:

- common/ubx_protocol: utility functions to encode and decode a ubx-format message.
- gnss: API to talk to a GNSS chip, either directly connected over a UART or indirectly connected via/inside a cellular module.
- cell/u_cell_loc.h: a new component in the cellular API to talk with Cell Locate.
- common/location: the generic location API that will work with any GNSS, cellular or short-range module.

cell/README.md

@@ -12,10 +12,11 @@ The cellular APIs are split into the following groups:
 - `sec_tls`: TLS security features.
 - `sock`: sockets, for exchanging data (but see the `common/sock` component for the best way to do this).
 - `mqtt`: MQTT client (but see the `common/mqtt_client` component for the best way to do this).
+- `loc`: getting a location fix using the Cell Locate service (but see the `common/location` component for the best way to do this); you will need an authentication token from the [Location Services section](https://portal.thingstream.io/app/location-services) of your [Thingstream portal](https://portal.thingstream.io/app/dashboard). If you have a GNSS chip attached via a cellular module and want to control it directly from your MCU, see the `gnss` API.
 
 The module types supported by this implementation are listed in `api/u_cell_module_type.h`.
 
-HOWEVER, this is the detailed API; if all you would like to do is bring up a bearer as simply as possible and then get on with exchanging data, please consider using the `common/network` API, along with the `common/sock`, `common/mqtt_client` and `common/security` APIs.  You may still dip down into this API from the network level as the handles used at the network level are the ones generated here.
+HOWEVER, this is the detailed API; if all you would like to do is bring up a bearer as simply as possible and then get on with exchanging data or establishing location, please consider using the `common/network` API, along with the `common/sock` API, the `common/security` API and the `common/location` API.  You may still dip down into this API from the network level as the handles used at the network level are the ones generated here.
 
 This API relies upon the `at_client` common component to send commands to and parse responses received from a cellular module.
 

cell/api/u_cell.h

@@ -109,7 +109,8 @@ typedef enum {
     U_CELL_ERROR_NOT_CONNECTED = U_ERROR_CELL_MAX - 7, /**< -263 if U_ERROR_BASE is 0. */
     U_CELL_ERROR_NOT_FOUND = U_ERROR_CELL_MAX - 8,  /**< -264 if U_ERROR_BASE is 0. */
     U_CELL_ERROR_VALUE_OUT_OF_RANGE = U_ERROR_CELL_MAX - 9,  /**< -265 if U_ERROR_BASE is 0. */
-    U_CELL_ERROR_TEMPORARY_FAILURE = U_ERROR_CELL_MAX - 10  /**< -266 if U_ERROR_BASE is 0. */
+    U_CELL_ERROR_TEMPORARY_FAILURE = U_ERROR_CELL_MAX - 10,  /**< -266 if U_ERROR_BASE is 0. */
+    U_CELL_ERROR_CELL_LOCATE = U_ERROR_CELL_MAX - 11  /**< -267 if U_ERROR_BASE is 0. */
 } uCellErrorCode_t;
 
 /* ----------------------------------------------------------------

cell/src/u_cell.c

@@ -171,6 +171,8 @@ void uCellDeinit()
             uCellPrivateScanFree(&(pInstance->pScanResults));
             // Free any chip to chip security context
             uCellPrivateC2cRemoveContext(pInstance);
+            // Free any location context and associated URC
+            uCellPrivateLocRemoveContext(pInstance);
             free(pInstance);
         }
 
@@ -230,6 +232,7 @@ int32_t uCellAdd(uCellModuleType_t moduleType,
                 pInstance->pModule = &(gUCellPrivateModuleList[moduleType]);
                 pInstance->pSecurityC2cContext = NULL;
                 pInstance->pMqttContext = NULL;
+                pInstance->pLocContext = NULL;
                 pInstance->pNext = NULL;
 
                 // Now set up the pins
@@ -364,6 +367,8 @@ void uCellRemove(int32_t cellHandle)
             uCellPrivateScanFree(&(pInstance->pScanResults));
             // Free any chip to chip security context
             uCellPrivateC2cRemoveContext(pInstance);
+            // Free any location context and associated URC
+            uCellPrivateLocRemoveContext(pInstance);
             free(pInstance);
         }