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docs: can send now

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Matthias Ringwald 2016-03-31 21:49:07 +02:00
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commit 5a4640bd78
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317
doc/manual/docs/protocols.md
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@ -199,29 +199,42 @@ in Listing [below](#lst:L2CAPremoteService).
btstack_packet_handler_t l2cap_packet_handler;
void btstack_setup(){
...
l2cap_init();
void l2cap_packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
bd_addr_t event_addr;
switch (packet_type){
case HCI_EVENT_PACKET:
switch (hci_event_packet_get_type(packet)){
case L2CAP_EVENT_CHANNEL_OPENED:
l2cap_event_channel_opened_get_address(packet, &event_addr);
psm = l2cap_event_channel_opened_get_psm(packet);
local_cid = l2cap_event_channel_opened_get_local_cid(packet);
handle = l2cap_event_channel_opened_get_handle(packet);
if (l2cap_event_channel_opened_get_status(packet)) {
printf("Connection failed\n\r");
} else
printf("Connected\n\r");
}
break;
case L2CAP_EVENT_CHANNEL_CLOSED:
break;
...
}
case L2CAP_DATA_PACKET:
// handle L2CAP data packet
break;
...
}
}
void create_outgoing_l2cap_channel(bd_addr_t address, uint16_t psm, uint16_t mtu){
l2cap_create_channel(NULL, l2cap_packet_handler, remote_bd_addr, psm, mtu);
}
void l2cap_packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
if (packet_type == HCI_EVENT_PACKET &&
packet[0] == L2CAP_EVENT_CHANNEL_OPENED){
if (packet[2]) {
printf("Connection failed\n\r");
return;
}
printf("Connected\n\r");
}
if (packet_type == L2CAP_DATA_PACKET){
// handle L2CAP data packet
return;
}
void btstack_setup(){
...
l2cap_init();
}
~~~~
### Provide an L2CAP service
@ -231,64 +244,62 @@ must init the L2CAP layer and register the service with
*l2cap_register_service*. From there on, it can wait for
incoming L2CAP connections. The application can accept or deny an
incoming connection by calling the *l2cap_accept_connection*
and *l2cap_deny_connection* functions respectively. If a
connection is accepted and the incoming L2CAP channel gets successfully
opened, the L2CAP service can send L2CAP data packets to the connected
device with *l2cap_send*.
and *l2cap_deny_connection* functions respectively.
Sending of L2CAP data packets may fail due to a full internal BTstack
outgoing packet buffer, or if the ACL buffers in the Bluetooth module
become full, i.e., if the application is sending faster than the packets
can be transferred over the air.
If a connection is accepted and the incoming L2CAP channel gets successfully
opened, the L2CAP service can send and receive L2CAP data packets to the connected
device with *l2cap_send*.
Listing [below](#lst:L2CAPService)
provides L2CAP service example code.
~~~~ {#lst:L2CAPService .c caption="{Providing an L2CAP service.}"}
void packet_handler (uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
bd_addr_t event_addr;
switch (packet_type){
case HCI_EVENT_PACKET:
switch (hci_event_packet_get_type(packet)){
case L2CAP_EVENT_INCOMING_CONNECTION:
local_cid = l2cap_event_incoming_connection_get_local_cid(packet);
l2cap_accept_connection(local_cid);
break;
case L2CAP_EVENT_CHANNEL_OPENED:
l2cap_event_channel_opened_get_address(packet, &event_addr);
psm = l2cap_event_channel_opened_get_psm(packet);
local_cid = l2cap_event_channel_opened_get_local_cid(packet);
handle = l2cap_event_channel_opened_get_handle(packet);
if (l2cap_event_channel_opened_get_status(packet)) {
printf("Connection failed\n\r");
} else
printf("Connected\n\r");
}
break;
case L2CAP_EVENT_CHANNEL_CLOSED:
break;
...
}
case L2CAP_DATA_PACKET:
// handle L2CAP data packet
break;
...
}
}
void btstack_setup(){
...
l2cap_init();
l2cap_register_service(NULL, packet_handler, 0x11,100);
}
void packet_handler (uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
...
if (packet_type == L2CAP_DATA_PACKET){
// handle L2CAP data packet
return;
}
switch(event){
...
case L2CAP_EVENT_INCOMING_CONNECTION:
bt_flip_addr(event_addr, &packet[2]);
handle = little_endian_read_16(packet, 8);
psm = little_endian_read_16(packet, 10);
local_cid = little_endian_read_16(packet, 12);
printf("L2CAP incoming connection requested.");
l2cap_accept_connection(local_cid);
break;
case L2CAP_EVENT_CHANNEL_OPENED:
bt_flip_addr(event_addr, &packet[3]);
psm = little_endian_read_16(packet, 11);
local_cid = little_endian_read_16(packet, 13);
handle = little_endian_read_16(packet, 9);
if (packet[2] == 0) {
printf("Channel successfully opened.");
} else {
printf("L2CAP connection failed. status code.");
}
break;
case L2CAP_EVENT_CAN_SEND_NOW:
send_now();
break;
case L2CAP_EVENT_CHANNEL_CLOSED:
break;
}
}
~~~~
### L2CAP - Sending packets {#sec:l2capFlowControlProtocols}
### Sending L2CAP Data {#sec:l2capSendProtocols}
Sending of L2CAP data packets may fail due to a full internal BTstack
outgoing packet buffer, or if the ACL buffers in the Bluetooth module
become full, i.e., if the application is sending faster than the packets
can be transferred over the air.
Instead of directly calling *l2cap_send*, it is recommended to call
*l2cap_request_can_send_now_event* which will trigger an L2CAP_EVENT_CAN_SEND_NOW
@ -296,7 +307,6 @@ as soon as possible. This might be even be immediately from inside the
*l2cap_request_can_send_now_event*. On L2CAP_EVENT_CAN_SEND_NOW, sending to the
channel indicated in the event is guaranteed to succedd.
## RFCOMM - Radio Frequency Communication Protocol
The Radio frequency communication (RFCOMM) protocol provides emulation
@ -348,30 +358,39 @@ Listing [below](#lst:RFCOMMremoteService).
~~~~ {#lst:RFCOMMremoteService .c caption="{RFCOMM handler for outgoing RFCOMM channel.}"}
void init_rfcomm(){
...
rfcomm_init();
rfcomm_register_packet_handler(packet_handler);
void rfcomm_packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
switch (packet_type){
case HCI_EVENT_PACKET:
switch (hci_event_packet_get_type(packet)){
case RFCOMM_EVENT_OPEN_CHANNEL_COMPLETE:
if (rfcomm_event_open_channel_complete_get_status(packet)) {
printf("Connection failed\n\r");
} else {
printf("Connected\n\r");
}
break;
case RFCOMM_EVENT_CHANNEL_CLOSED:
break;
...
}
break;
case RFCOMM_DATA_PACKET:
// handle RFCOMM data packets
return;
}
}
void create_rfcomm_channel(uint8_t packet_type, uint8_t *packet, uint16_t size){
rfcomm_create_channel(connection, addr, rfcomm_channel);
rfcomm_create_channel(rfcomm_packet_handler, addr, rfcomm_channel);
}
void rfcomm_packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
if (packet_type == HCI_EVENT_PACKET && packet[0] == RFCOMM_EVENT_OPEN_CHANNEL_COMPLETE){
if (packet[2]) {
printf("Connection failed\n\r");
return;
}
printf("Connected\n\r");
}
if (packet_type == RFCOMM_DATA_PACKET){
// handle RFCOMM data packets
return;
}
void btstack_setup(){
...
l2cap_init();
rfcomm_init();
}
~~~~
### Provide an RFCOMM service {#sec:rfcommServiceProtocols}
@ -381,61 +400,58 @@ device must first init the L2CAP and RFCOMM layers and then register the
service with *rfcomm_register_service*. From there on, it
can wait for incoming RFCOMM connections. The application can accept or
deny an incoming connection by calling the
*rfcomm_accept_connection* and
*rfcomm_deny_connection* functions respectively. If a
connection is accepted and the incoming RFCOMM channel gets successfully
*rfcomm_accept_connection* and *rfcomm_deny_connection* functions respectively.
If a connection is accepted and the incoming RFCOMM channel gets successfully
opened, the RFCOMM service can send RFCOMM data packets to the connected
device with *rfcomm_send* and receive data packets by the
packet handler provided by the *rfcomm_register_service*
call.
Listing [below](#lst:RFCOMMService)
provides the RFCOMM service example code.
Listing [below](#lst:RFCOMMService) provides the RFCOMM service example code.
~~~~ {#lst:RFCOMMService .c caption="{Providing an RFCOMM service.}"}
void packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
switch (packet_type){
case HCI_EVENT_PACKET:
switch (hci_event_packet_get_type(packet)){
case RFCOMM_EVENT_INCOMING_CONNECTION:
rfcomm_channel_id = rfcomm_event_incoming_connection_get_rfcomm_cid(packet);
rfcomm_accept_connection(rfcomm_channel_id);
break;
case RFCOMM_EVENT_OPEN_CHANNEL_COMPLETE:
if (rfcomm_event_open_channel_complete_get_status(packet)){
printf("RFCOMM channel open failed.");
break;
}
rfcomm_channel_id = rfcomm_event_open_channel_complete_get_rfcomm_cid(packet);
mtu = rfcomm_event_open_channel_complete_get_max_frame_size(packet);
printf("RFCOMM channel open succeeded, max frame size %u.", mtu);
break;
case RFCOMM_EVENT_CHANNEL_CLOSED:
printf("Channel closed.");
break;
...
}
break;
case RFCOMM_DATA_PACKET:
// handle RFCOMM data packets
return;
...
}
...
}
void btstack_setup(){
...
l2cap_init();
rfcomm_init();
rfcomm_register_service(NULL, rfcomm_channel_nr, mtu);
rfcomm_register_service(packet_handler, rfcomm_channel_nr, mtu);
}
void packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
if (packet_type == RFCOMM_DATA_PACKET){
// handle RFCOMM data packets
return;
}
...
switch (packet[0]) {
...
case RFCOMM_EVENT_INCOMING_CONNECTION:
//data: event(8), len(8), address(48), channel(8), rfcomm_cid(16)
bt_flip_addr(event_addr, &packet[2]);
rfcomm_channel_nr = packet[8];
rfcomm_channel_id = little_endian_read_16(packet, 9);
rfcomm_accept_connection(rfcomm_channel_id);
break;
case RFCOMM_EVENT_OPEN_CHANNEL_COMPLETE:
// data: event(8), len(8), status (8), address (48), handle(16), server channel(8), rfcomm_cid(16), max frame size(16)
if (packet[2]) {
printf("RFCOMM channel open failed.");
break;
}
// data: event(8), len(8), status (8), address (48), handle (16), server channel(8), rfcomm_cid(16), max frame size(16)
rfcomm_channel_id = little_endian_read_16(packet, 12);
mtu = little_endian_read_16(packet, 14);
printf("RFCOMM channel open succeeded.");
break;
case RFCOMM_EVENT_CHANNEL_CLOSED:
printf("Channel closed.");
rfcomm_channel_id = 0;
break;
}
}
~~~~
### Living with a single output buffer {#sec:singleBufferProtocols}
### Sending RFCOMM data {#sec:rfcommSendProtocols}
Outgoing packets, both commands and data, are not queued in BTstack.
This section explains the consequences of this design decision for
@ -450,46 +466,25 @@ the RFCOMM send rate.
When there's a need to send a packet, call *rcomm_request_can_send_now*
directly and send the packet when the RFCOMM_EVENT_CAN_SEND_NOW event
gets received.
gets receive as shown in Listing [below](#lst:rfcommRequestCanSendNow).
Before sending data packets, check if RFCOMM can send them by calling
*rfcomm_can_send_packet_now*, as shown in Listing [below](#lst:SingleOutputBufferTryToSend).
Sending of RFCOMM data packets may fail due to a full internal BTstack
outgoing packet buffer, or if the ACL buffers in the Bluetooth module
become full, i.e., if the application is sending faster than the packets
can be transferred over the air.
RFCOMM’s mandatory credit-based flow-control imposes an additional
constraint on sending a data packet - at least one new RFCOMM credit
must be available. BTstack signals the availability of a credit by
sending an RFCOMM credit (RFCOMM_EVENT_CREDITS) event.
These two events represent two orthogonal mechanisms that deal with flow
control. BTstack provides a unified approach to send efficiently.
If calling *rfcomm_can_send_packet_now* returns false, and it is not possible to send right away,
BTstack will keep track of the applications request to send a packet and later emit an RFCOMM_EVENT_CAN_SEND_NOW
as soon as it becomes possible to send again. L2CAP, BNEP, and ATT API offer similar functionality.
For an RFCOMM example see Listing [below](#lst:SingleOutputBufferTryPH).
~~~~ {#lst:SingleOutputBufferTryToSend .c caption="{Preparing and sending data.}"}
~~~~ {#lst:rfcommRequestCanSendNow .c caption="{Preparing and sending data.}"}
void prepare_data(void){
...
// prepare data in data_buffer
rfcomm_request_can_send_now_event(rfcom_channel_id);
}
void send_data(void){
rfcomm_send(rfcomm_channel_id, dataBuffer, dataLen);
// packet is sent prepare next one
rfcomm_send(rfcomm_channel_id, data_buffer, data_len);
// packet is handed over to BTstack, we can prepare the next one
prepare_data();
}
void packet_handler(uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
switch (packet_type){
case HCI_EVENT_PACKET:
switch (packet[0]){
switch (hci_event_packet_get_type(packet)){
...
case RFCOMM_CAN_SEND_NOW:
send_data(;
@ -503,31 +498,6 @@ For an RFCOMM example see Listing [below](#lst:SingleOutputBufferTryPH).
~~~~
~~~~ {#lst:SingleOutputBufferTryPH .c caption="{Resending data packets.}"}
void packet_handler (uint8_t packet_type, uint16_t channel, uint8_t *packet, uint16_t size){
...
switch(event){
case RFCOMM_EVENT_OPEN_CHANNEL_COMPLETE:
if (status) {
printf("RFCOMM channel open failed.");
} else {
rfcomm_channel_id = little_endian_read_16(packet, 12);
rfcomm_mtu = little_endian_read_16(packet, 14);
printf("RFCOMM channel opened, mtu = %u.", rfcomm_mtu);
}
break;
case RFCOMM_EVENT_CAN_SEND_NOW:
tryToSend();
break;
case RFCOMM_EVENT_CHANNEL_CLOSED:
rfcomm_channel_id = 0;
break;
...
}
}
~~~~
### Slowing down RFCOMM data reception {#sec:manualCreditsProtocols}
RFCOMM’s credit-based flow-control can be used to adapt, i.e., slow down
@ -543,8 +513,7 @@ connection is used. See Listing [below](#lst:automaticFlowControl).
...
// init RFCOMM
rfcomm_init();
rfcomm_register_packet_handler(packet_handler);
rfcomm_register_service(NULL, rfcomm_channel_nr, 100);
rfcomm_register_service(packet_handler, rfcomm_channel_nr, 100);
}
~~~~
@ -552,7 +521,6 @@ If the management of credits is manual, credits are provided by the
application such that it can manage its receive buffers explicitly, see
Listing [below](#lst:explicitFlowControl).
Manual credit management is recommended when received RFCOMM data cannot
be processed immediately. In the [SPP flow control example](examples/generated/#sec:sppflowcontrolExample),
delayed processing of received data is
@ -565,9 +533,8 @@ and the number of credits as shown in Listing [below](#lst:NewCredits).
...
// init RFCOMM
rfcomm_init();
rfcomm_register_packet_handler(packet_handler);
// reserved channel, mtu=100, 1 credit
rfcomm_register_service_with_initial_credits(NULL, rfcomm_channel_nr, 100, 1);
rfcomm_register_service_with_initial_credits(packet_handler, rfcomm_channel_nr, 100, 1);
}
~~~~