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MAC API porting

Nanostack has a lower level API for the IEEE 802.15.4-2006 MAC standard. This enables developers to support different MACs, be it SW or HW based solutions. Nanostack offers SW MAC, which you can use when your board does not have 15.4 MAC available.

SW MAC

Nanostack includes an IEEE 802.15.4 based SW MAC class. You can use SW MAC when your board does not support MAC. To use the SW MAC service you must have a working RF driver registered to Nanostack. To create SW MAC, call the following function:

ns_sw_mac_create()

This creates an SW MAC class and sets a callback function to be used by Nanostack.

Note: You must not call ns_sw_mac_create() more than once!

Initializing SW MAC

Deploy SW MAC as follows:

  1. Call arm_net_phy_register() to register the configured RF driver class to Nanostack.
  2. Call ns_sw_mac_create() to create SW MAC with needed list sizes.
    • a sleepy device needs only 1-4 as the size of the device_decription_table_size.
    • the minimum and recommended key_description_table_size for the Thread stack is 4. (2 for 6LoWPAN)
    • the recommended value for key_lookup_size is 1 and for key_usage_size 3.
  3. Call arm_nwk_interface_lowpan_init() to create Nanostack with the created SW MAC class. Nanostack will initialize SW MAC before using it.

Example

See a simple code snippet for creating SW MAC with 16 as neighbor table size with three key descriptions:

int8_t generate_6lowpan_interface(int8_t rf_phy_device_register_id)
{
    mac_description_storage_size_t storage_sizes;
    storage_sizes.device_decription_table_size = 16;
    storage_sizes.key_description_table_size = 3;
    storage_sizes.key_lookup_size = 1;
    storage_sizes.key_usage_size = 3;
    mac_api_t *mac_api = ns_sw_mac_create(rf_phy_device_register_id, &storage_sizes);
    if (!mac_api) {
        tr_error("Mac create fail!");
        return -1;
    }
    return arm_nwk_interface_lowpan_init(mac_api, "6LoWPAN_ROUTER");
}

Enabling FHSS

SW MAC supports FHSS. To enable it, you need to do the following:

  1. Call arm_net_phy_register() to register the configured RF driver class to Nanostack.
  2. Call ns_sw_mac_create() to create SW MAC with needed list sizes.
  3. Call ns_fhss_create() to configure and define the FHSS class.
  4. Call ns_sw_mac_fhss_register() to register FHSS to SW MAC.
  5. Call arm_nwk_interface_lowpan_init() to create Nanostack with the created SW MAC class.

IEEE 802.15.4 MAC sublayer APIs

The stack uses the IEEE 802.15.4 defined MAC management service entity (MLME-SAP) and MAC data service (MCPS-SAP) interfaces. MAC API follows MCPS and MLME primitives defined by the IEEE 802.15.4-2006 standard.

The following primitives are used in MAC layer:

Primitive Description
Request Request made by service user.
Confirm MAC layer response to earlier request.
Indication Indication event from MAC to service user.
Response Service user's response to received indication.

MAC API is defined in the following header files:

  • mac_api.h Main header which defines a transparent MAC API for Nanostack to use.
  • mlme.h Definitions for MLME-SAP primitives.
  • mac_mcps.h Definitions for MCPS-SAP primitives.
  • mac_common_defines.h Definitions for common MAC constants.

MCPS-SAP interface

MCPS-SAP defines 802.15.4 data flow API with the following primitives:

Primitive Description
MCPS-DATA-REQ Data request primitive to MAC.
MCPS-DATA-CONF MAC generated confirmation for ongoing MCPS-DATA-REQ.
MCPS-DATA-IND MAC generated data indication event.
MCPS-PURGE-REQ Cancel ongoing MCPS-DATA-REQ from MAC.
MCPS-PURGE-CONF Confirmation from MAC to MCPS-PURGE-REQ operation.

MLME-SAP interface

MLME-SAP defines a set of different management primitives and this chapter introduces both supported and unsupported primitives in Nanostack.

Supported MLME APIs

MLME-SAP primitives used by Nanostack:

Primitive Description
MLME-BEACON-NOTIFY MAC generated event for received beacons.
MLME-GET-REQ Request information about a specified PAN Information Base (PIB) attribute.
MLME-GET-CONF MAC generated response to MLME-GET-REQ.
MLME-RESET-REQ Request to reset MAC to idle state and clean data queues.
MLME-SCAN-REQ Start MAC scan process. Orphan scan is not supported.
MLME-SCAN-CONF Result of the scan made by MLME-SCAN-REQ.
MLME-COMM-STATUS-IND MAC generated indication about the communications status.
MLME-SET-REQ Request to write data into a specified PIB attribute.
MLME-SET-CONF MAC generated response to MLME-SET-REQ.
MLME-START-REQ Starts or enables MAC with specified options. Nanostack uses this also for RFD devices.
MLME-SYNCH-LOSS-IND Indicates synchronization loss from wireless PAN. Only used by SW MAC when FHSS is in use!
MLME-POLL-REQ Request MAC to do data poll to parent.

Unsupported MLME APIs

Unsupported MLME-SAP primitives:

Primitive Support planned Description
MLME-ASSOCIATE-REQ Not yet Start MAC association process.
MLME-ASSOCIATE-CONF Not yet MAC association process confirmation status.
MLME-ASSOCIATE-IND Not yet MAC association indication to indicate the reception of assocation request.
MLME-ASSOCIATE-RES Not yet MAC association response for indication.
MLME-DISASSOCIATE-REQ Not yet MAC disassociation request from service user.
MLME-DISASSOCIATE-IND Not yet MAC disassociation indication event to service user.
MLME-DISASSOCIATE-CONF Not yet MAC disassociation confirmation when the disassociation request is handled.
MLME-GTS-REQ Not yet MAC Guaranteed Time Slot (GTS) request.
MLME-GTS-IND Not yet MAC GTS allocate event indication.
MLME-GTS-CONF Not yet MAC GTS request confirmation.
MLME-ORPHAN-IND Not yet Service user indicated by orphaned device.
MLME-ORPHAN-RES Not yet Service user response to orphan indication event.
MLME-RESET-CONF Yes MAC reset confirmation.
MLME-RX-ENABLE-REQ Yes Enable (or disable) RX receiver for a specified time.
MLME-RX-ENABLE-CONF Yes Confirmation for MLME-RX-ENABLE-REQ.
MLME-START-CONF Yes Confirmation for MLME start request.
MLME-SYNCH-REQ Not yet Request MAC to synchronize with coordinator.

MAC API class introduction

This chapter introduces MAC mesh interface mac_api_s. It is a structure that defines the function callbacks needed by a service user.

The base class defines the functions for two-way communications between an external MAC and service user. The application creates a mac_api_s object by calling the MAC adapter's create function. The newly created object is then passed to Nanostack which initializes its own callback functions by calling the mac_api_initialize() function. A service user operates MAC by calling MLME or MCPS primitive functions.

The MAC API class structure mac_api_t is defined as below:

typedef struct mac_api_s {
    //Service user defined initialization function which is called when Nanostack takes MAC into use
    mac_api_initialize              *mac_initialize;
    //MAC adapter function callbacks for MLME & MCPS SAP
    mlme_request                    *mlme_req;
    mcps_data_request               *mcps_data_req;
    mcps_purge_request                  *mcps_purge_req;
    //Service user defined function callbacks
    mcps_data_confirm               *data_conf_cb;
    mcps_data_indication                *data_ind_cb;
    mcps_purge_confirm                  *purge_conf_cb;
    mlme_confirm                        *mlme_conf_cb;
    mlme_indication                     *mlme_ind_cb;
    //MAC extension API for service user
    mac_ext_mac64_address_set           *mac64_set;
    mac_ext_mac64_address_get           *mac64_get;
    mac_storage_decription_sizes_get *mac_storage_sizes_get;
    int8_t                              parent_id;
    uint16_t                            phyMTU;
};
Member Description
mac_initialize MAC initialize function called by Nanostack.
mlme_req MLME request function to use MLME-SAP commands, MAC defines.
mcps_data_req MCPS data request function to use, MAC defines.
mcps_purge_req MCPS purge request function to use, MAC defines.
mcps_data_confirm MCPS data confirm callback function, service user defines.
data_ind_cb MCPS data indication callback function, service user defines.
purge_conf_cb MCPS purge confirm callback function, service user defines.
mlme_conf_cb MLME confirm callback function, service user defines.
mlme_ind_cb MLME indication callback function, service user defines.
mac64_set MAC extension function to set mac64 address.
mac64_get MAC extension function to get mac64 address.
mac_storage_sizes_get Getter function to query data storage sizes from MAC.
parent_id Service user ID used to indentify the MAC service user. Optional.
phyMTU Maximum Transmission Unit (MTU) used by MAC. Standard 802.15.4 MAC must set 127.

MAC API standard extensions

This chapter introduces MAC API standard extensions.

MAC 64-bit address set and get

NanoStack uses 64-bit address set and get. There are two 64-bit addresses available:

  • NVM EUI64.
  • dynamic 64-bit address used at the link layer.

Thread generates a random MAC64 after commissioning. Therefore, MAC and the RF driver must support updating of radio's dynamic 64-bit address anytime.

Address set and get support two different 64-bit addresses:

Address enumeration type Description
MAC_EXTENDED_READ_ONLY A unique EUI64.
MAC_EXTENDED_DYNAMIC Dynamic 64-bit address. Same as EUI64 after boot.

MAC max storage information get

Usually, HW MAC and SW MAC have static keys and neighbor list sizes. Nanostack always asks the max size to limit its neighbor table size. The service user must define the mac_storage_sizes_get() function returning the following values:

  • MAC Device description list size (must be > 1).
  • MAC Key description list size (must be > 1).

Note: The Key description list size must be at least 4 if using Thread!

MLME attribute extension

Nanostack uses MLME attribute extensions which have to be ported to the HW MAC adapter. To configure the extensions, use the MLME-SET-REQ command.

Enumeration type Value Description
macLoadBalancingBeaconTx 0xfd Trigger to MAC layer to send a beacon. Called by the load balancer module periodically.
macLoadBalancingAcceptAnyBeacon 0xfe Configure MAC layer to accept beacons from other networks. Enabled by load balancer, default value is False. Value size boolean, true=enable, false=disable.
macThreadForceLongAddressForBeacon 0xff The Thread standard forces the beacon source address to have an extended 64-bit address.

Thread Sleepy End Device (SED) keepalive extension

Thread 1.1 stack defines that the sleepy end device data poll process must enable the neighbor table keepalive functionality as well. When SED finishes data polling successfully, it updates its parents keepalive value in a neighbor table. A service user at a parent device does not have a standard mechanism to indicate the data polling event. Therefore, the MAC layer must generate an MLME-COMM-STATUS indication callback with status MLME_DATA_POLL_NOTIFICATION.

Enumeration extension for MLME communication status enumeration:

Enumeration type Value Description
MLME_DATA_POLL_NOTIFICATION 0xff Thread requirement for MLME-COMM-STATUS to start indicating the successful data poll events.

HW MAC

To use HW MAC, you need to create an adapter class that links function calls between Nanostack and HW MAC. To create the adapter class, you need to implement the functions defined in the mac_api_s structure. When HW MAC generates an event, the adapter must handle it and do a parameter adaptation before calling the correct function from the mac_api_s structure. You may need the same parameter adaptation for requests from Nanostack to HW MAC.

Note: Function calls from Nanostack to HW MAC must be non-blocking in the adapter layer!

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