nes-proj/doc/example-packet-drv.c

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/*
* This is an example of how to write a network device driver ("packet
* driver") for Contiki. A packet driver is a regular Contiki process
* 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 TCP/IP stack,
* whereas incoming packets must be checked inside a Contiki process.
* We use the same process for checking for incoming packets and for
* registering the output function.
*/
/*
* 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 with the TCP/IP stack,
* and to check for incoming packets.
*/
PROCESS(example_packet_driver_process, "Example packet driver 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.
*/
uint8_t
example_packet_driver_output(void)
{
let_the_hardware_send_the_packet(uip_buf, uip_len);
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/*
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* A network device driver returns always zero.
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*/
return 0;
}
/*---------------------------------------------------------------------------*/
/*
* 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_driver_process);
}
/*---------------------------------------------------------------------------*/
/*
* Finally, we define the process that does the work.
*/
PROCESS_THREAD(example_packet_driver_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());
/*
* This process has an exit handler, so we declare it here. Note that
* the PROCESS_EXITHANDLER() macro must come before the PROCESS_BEGIN()
* macro.
*/
PROCESS_EXITHANDLER(exithandler());
/*
* The process begins here.
*/
PROCESS_BEGIN();
/*
* We start with initializing the hardware.
*/
initialize_the_hardware();
/*
* Register the driver. This will cause any previously registered driver
* to be ignored by the TCP/IP stack.
*/
tcpip_set_outputfunc(example_packet_driver_output);
/*
* Now we'll make sure that the poll handler is executed initially. We do
* this by calling process_poll() with this process as its argument.
*/
process_poll(&example_packet_driver_process);
/*
* And we wait for the process to exit.
*/
PROCESS_WAIT_EVENT_UNTIL(ev == PROCESS_EVENT_EXIT);
/*
* Now we shutdown the hardware.
*/
shutdown_the_hardware();
/*
* Here ends the process.
*/
PROCESS_END();
}
/*---------------------------------------------------------------------------*/