Creating BGAPIv2 backend

[matt7aylor]

The bgapi backend in pygatt supports the command set for the BlueGiga devices, these use BGAPI v1 https://www.silabs.com/documents/public/reference-manuals/Bluetooth_Smart_Software-BLE-1.4-API-RM.pdf

We want to create a backend that will support the new Silicon Labs devices that use a newer (incompatible) version of the BGAPI v2 https://docs.silabs.com/bluetooth/latest/ (and maybe in future even the Bluetooth Mesh version of BGAPI https://www.silabs.com/documents/public/reference-manuals/bluetooth-le-and-mesh-software-api-reference-manual.pdf )

The plan for this should be:

• [ ] Identify which parts of the bgapi backend will need to be changed in the bgapi2 backend. Can we preserve most of the backend as is and just point to a new API?
  • [ ] bgapi.py - Changes:
  • Remove find_usb_serial_devices() and BLED112 hardcoding
  • May need to update some commands if commands themselves (not just packet structure) have changed
  • [ ] bglib.py - All responses/events need remapping/changing
  • [ ] constants.py - Need to replace scan_response_packet_type with new binary processor
  • [ ] device.py - Need to check commands are still suitable
  • [ ] error_codes.py - Error codes seem compatible between versions, can add a few new ones from https://docs.silabs.com/bluetooth/latest/error-codes
  • [x] exceptions.py - No Change
  • [ ] packets.py - All commands need changing/updating
  • [ ] util.py - Remove as USBSerial functions are not required?
• [x] Identify the changes in basic packet structure between versions
• [x] Identify which commands/functions from v1 have been removed or replaced in v2 and will need more work.
• [ ] Identify any new commands/packets that will be needed in v2
• [ ] Change the command/packet processing to use new v2 structure

[matt7aylor]

Initial test of commands in commit 9225f3ed391917501bfb82fb3feca9528cae0fc2 supports going as far as adapter.get_mac()

import pygatt
import logging 
logging.basicConfig()
logging.getLogger('pygatt').setLevel(logging.DEBUG)
PORT='/dev/pts/10'
adapter = pygatt.BGAPIBackend(serial_port=PORT)
adapter.start()
adapter.get_mac()
mac = adapter.address

[matt7aylor]

A list of all commands/ResponsePacketType used by bgapi v1. We will want to make sure we migrate all these command to their v2 equivalent to reproduce functionality, then we could think about adding extra commands if desired.

In bgapi.py:

• [x] system_reset - same form
• [x] system_address_get -> system_get_bt_address (same form)
• [x] gap_end_procedure -> le_gap_end_procedure (same form)
• [x] gap_set_scan_parameters -> le_gap_set_scan_parameters (same form but) DEPRECATED
• [x] gap_discover -> le_gap_discover (same form but) DEPRECATED
• [x] gap_set_mode -> le_gap_set_mode (same form but) DEPRECATED
• [x] gap_connect_direct -> le_gap_connect CHANGED similar but will need some work
• [x] attclient_find_information - CHANGED will need to change discover_characteristics to use gatt_discover_primary_services and gatt_discover_characteristics with the new events (wait for and process events until gatt_procedure_completed)
• [ ] sm_get_bonds -> CHANGED sm_list_all_bondings and new sm_list_bonding_entry events and sm_list_all_bondings_complete event
• [ ] sm_delete_bonding - same form
• [ ] sm_set_bondable_mode - same

In device.py:

• [ ] connection_get_rssi -> le_connection_get_rssi (same form)
• [x] connection_disconnect -> le_connection_close (same form)
• [ ] attclient_read_by_handle -> gatt_read_characteristic_value (looks pretty similar but is now doing same as read_long so need to check will work for both)
  • events: gatt_characteristic_value , gatt_procedure_completed
• [ ] attclient_read_long - gatt_read_characteristic_value is read_long
• [ ] attclient_attribute_write -> gatt_write_characteristic_value and process event
• [ ] attclient_write_command -> gatt_write_characteristic_value_without_response
• [ ] attclient_prepare_write -> gatt_prepare_characteristic_value_write (same form)
• [ ] attclient_execute_write -> gatt_execute_characteristic_value_write (same form)
• [ ] sm_encrypt_start -> sm_increase_security - slightly different form, may need to look at bond function in device.py

EventPacketType expected by pygatt v1. In bgapi.py:

• [ ] attclient_attribute_value -> gatt_characteristic_value (similar), type (att_opcode) numbers are different but these aren't really used, not sure what offset does. Will need to use service, characteristic and descriptor attributes separately in new code
• [ ] attclient_find_information_found - CHANGED need to rewrite characteristic discovery to use new commands/events with separate service/char/desc
• [ ] attclient_procedure_completed -> gatt_procedure_completed (similar)
• [x] connection_status -> le_connection_parameters (similar)
• [x] connection_disconnected -> le_connection_closed (similar)
• [x] gap_scan_response - le_gap_scan_response (similar) needs a new processor for packet_type (and maybe more)
  • [ ] Improve packet processing and add extra packet types (extended advertising etc.)
• [ ] sm_bond_status -> sm_bonded - need to change bond() in device to expect new events (le_connection_parameters and sm_bonded ) / sm_bonding_failed

In device.py

• [ ] sm_bonding_fail -> sm_bonding_failed (similar) need to change bond() in device to expect new events (le_connection_parameters and sm_bonded ) / sm_bonding_failed

[matt7aylor]

Basic support for adapter.scan() as of 1d96cb21a7bc3adbb3b20abdfe5a8e465434a571

[matt7aylor]

Basic connect/disconnect functionality in 0b052a3 . Need to manually change address_type to random for connecting to Thingy52, not sure why dev = adapter.connect('FB:91:81:28:F7:74', address_type=1). No processing of characteristics yet.