task-07

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Task 7: The GNRC network stack

This task is a little bit more advanced so don't be discouraged if things are a little bit harder. With the knowledge you gathered from the previous tasks you should be able to handle it.

It uses the example applications in the RIOT repository.

Task 7.1: Compile the gnrc_minimal application

• Go to the gnrc_minimal application
• Compile and run on native
• Should print something like My address is fe80::d403:24ff:fe89:2460
• Ping RIOT instance from Linux:

ping <RIOT-IPv6-addr>%tapbr0

Note: on MAC use bridge0 instead of tapbr0.

Task 7.2: Extend gnrc_minimal application

• Add the gnrc_udp module to the application's Makefile
• To be able to receive packets, a message queue must be created using msg_init_queue:

msg_t msg_queue[num];
msg_init_queue(msg_queue, num);

Note: num must be in powers of 2.

• You can register for packets of a certain type and context (port 8888 in our case) using gnrc_netreg_register() from net/gnrc/netreg.h:
• The current thread can be obtained with the thread_getpid() function from thread.h

gnrc_netreg_entry_t server = GNRC_NETREG_ENTRY_INIT_PID(8888, thread_getpid());
gnrc_netreg_register(GNRC_NETTYPE_UDP, &server);

• Packets can be received using the IPC receive function msg_receive():

msg_t msg;
msg_receive(&msg);

Remember to remove the packet after reception (otherwise the packet buffer will overflow)!

#include "net/gnrc/pktbuf.h"

/* ... */

gnrc_pktsnip_t *pkt = (gnrc_pktsnip_t *)msg.content.ptr;
gnrc_pktbuf_release(pkt);

1. Extend gnrc_minimal as such that it counts received UDP packets on port 8888.
2. Use netcat on your host to test your application on native node.

Task 7.3: Send your neighbor some messages again

• Go to the gnrc_networking application
• Have a look in udp.c how packets are constructed and send
• Compile, flash, and run on the board BOARD=samr21-xpro make all flash term
• Type help
• Start UDP server on port 8888 using udp server 8888
• Get your IPv6 address using ifconfig
• Send your neighbor some messages using udp send

Read the Doc

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