osd-contiki/doc/example-packet-service.c

142 lines
4.6 KiB
C

/*
* This is an example of how to write a network device driver ("packet
* service") for Contiki. A packet service is a regular Contiki
* service that does two things:
* # Checks for incoming packets and delivers those to the TCP/IP stack
* # Provides an output function that transmits packets
*
* The output function is registered with the Contiki service
* mechanism, whereas incoming packets must be checked inside a
* Contiki process. We use the same process for checking for incoming
* packets and for registering the service.
*
* NOTE: This example does not work with the uip-fw module (packet
* forwarding with multiple interfaces). It only works with a single
* interface.
*/
/*
* We include the "contiki-net.h" file to get all the network
* functions.
*/
#include "contiki-net.h"
/*---------------------------------------------------------------------------*/
/*
* We declare the process that we use to register the service, and to
* check for incoming packets.
*/
PROCESS(example_packet_service_process, "Example packet service process");
/*---------------------------------------------------------------------------*/
/*
* This is the poll handler function in the process below. This poll
* handler function checks for incoming packets and delivers them to
* the TCP/IP stack.
*/
static void
pollhandler(void)
{
/*
* We assume that we have some hardware device that notifies us when
* a new packet has arrived. We also assume that we have a function
* that pulls out the new packet (here called
* check_and_copy_packet()) and puts it in the uip_buf[] buffer. The
* function returns the length of the incoming packet, and we store
* it in the global uip_len variable. If the packet is longer than
* zero bytes, we hand it over to the TCP/IP stack.
*/
uip_len = check_and_copy_packet();
/*
* The function tcpip_input() delivers the packet in the uip_buf[]
* buffer to the TCP/IP stack.
*/
if(uip_len > 0) {
tcpip_input();
}
/*
* Now we'll make sure that the poll handler is executed
* repeatedly. We do this by calling process_poll() with this
* process as its argument.
*
* In many cases, the hardware will cause an interrupt to be
* executed when a new packet arrives. For such hardware devices,
* the interrupt handler calls process_poll() (which is safe to use
* in an interrupt context) instead.
*/
process_poll(&example_packet_service_process);
}
/*---------------------------------------------------------------------------*/
/*
* Next, we define the function that transmits packets. This function
* is called from the TCP/IP stack when a packet is to be
* transmitted. The packet is located in the uip_buf[] buffer, and the
* length of the packet is in the uip_len variable.
*/
static void
send_packet(void)
{
let_the_hardware_send_the_packet(uip_buf, uip_len);
}
/*---------------------------------------------------------------------------*/
/*
* Now we declare the service. We call the service
* example_packet_service because of the name of this file. The
* service should be an instance of the "packet service" service, so
* we give packet_service as the second argument. Finally we give our
* send_packet() function as the last argument, because of how the
* packet_service interface is defined.
*
* We'll register this service with the Contiki system in the process
* defined below.
*/
SERVICE(example_packet_service, packet_service, { send_packet });
/*---------------------------------------------------------------------------*/
/*
* Finally, we define the process that does the work.
*/
PROCESS_THREAD(example_packet_service_process, ev, data)
{
/*
* This process has a poll handler, so we declare it here. Note that
* the PROCESS_POLLHANDLER() macro must come before the
* PROCESS_BEGIN() macro.
*/
PROCESS_POLLHANDLER(pollhandler());
/*
* The process begins here.
*/
PROCESS_BEGIN();
/*
* We start with initializing the hardware.
*/
initialize_the_hardware();
/*
* Register the service. This will cause any other instances of the
* same service to be removed.
*/
SERVICE_REGISTER(example_packet_service);
/*
* And we wait for either the process to exit, or for the service to
* be removed (by someone else).
*/
PROCESS_WAIT_EVENT_UNTIL(ev == PROCESS_EVENT_EXIT ||
ev == PROCESS_EVENT_SERVICE_REMOVED);
/*
* And we always end with explicitly removing the service.
*/
SERVICE_REMOVE(example_packet_service);
/*
* Here endeth the process.
*/
PROCESS_END();
}
/*---------------------------------------------------------------------------*/