The demo code will be used by everyone in lab as a starting point for their own code.
To avoid stepping on each other's data, you MUST set AP addresses to a unique value to avoid interference.
For the AP and station examples, my default AP address is 192.168.4.1.
-- Change the AP address to 192.168.myAP.1. You may need to negotiate the value of myAP
(integer values between 2 and 255) with other groups who are close by in the room.
-- You then need to change the station address to match the AP subnet,
so 192.168.myAP.mySTATION with mySTATION>1.
(192.168 is widely used for local networks).
For picoW stations that are connecting to hotspots (e.g. cellphone), the address will be set by DHCP and should be unique.
For best distance range, clear metal from under and over antenna including wires, solderless board, and ground planes.
I have gotten around 5 meters range between picoWs in a quiet WIFI environment.
The antenna is a 12x17mm region of the picoW board consisting of a area clear of ground plane, with two precisely placed traces. (see below).
The antenna is described in the datasheet. When communicating between two picoWs, pay attention to orientation of antennas. Accoring to the datasheet, max radiation direction is from the edge of the board where the antenna is located, and in an horizontal plane.
(see diagram below, but note that on our board the antenna is on a narrow side of the board).
There is a utility for reading the RSSI (Received Signal Strength Indicator),
if the picoW is a station, and if it is connected to an AP.
int32_t rssi ; cyw43_wifi_get_rssi (&cyw43_state, &rssi); printf("rssi=%d\n\r", rssi) ;
Normal range for RSSI would be -45db to -90db, less than -90 is marginal.
Greater than -70 is generally good.
In the two images below, the Wifi antenna is at the left end of the board. The top image
shows the traces on top of the board. The bottom image uses light from below the board to shows
that the region with no ground plane is a trapzoid, with the narrow side at the left edge of the board.
The keep metal away region is therefore all the space across the board, between the last 3 pins on the left end of the board.
You may need to change the WIFI channel for best noise. Note that you only change channels on APs. Stations adapt to AP channel.
All the boards default to WIFI channel 3, but typical routers use 1, 6, or 11.
If channel 3 is noisy, try 11. Most routers default to 6.
Any value from 1 to 13 is legal in USA, but you should read https://en.wikipedia.org/wiki/List_of_WLAN_channels before blindly changing channels.
To set the channel of an AP to 6: cyw43_wifi_ap_set_channel(&cyw43_state, 6); To find out which channel the AP is using: printf("AP_channel %d\n\r", cyw43_state.ap_channel);
We are using the LWIP package in the NO_SYS=1 mode. This implies that LWIP will start callback functions to handle async network requests, e.g., packet receive, packet ack. Typically you will write protothreads which will be signalled from the callbacks to perfrom some action. For good performance, you will need to use the priority scheduler (Protothreads_1.3) and be sure that the thread handling the receive callback results is high priority.
More generally, many of the LWIP functions are async, so that you need to carefully synchronize LWIP funcitons with threads.
Never assume that a LWIP funciion is blocking, unless the documentation explicitly says so.
There is much more to say about software, but much of it is in the examples on the projects page.