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Using USB WiFi with SmartFusion2 under uClinux Print

 

This application note explains how to use a USB WiFi module with SmartFusion2 under uClinux. The demo described in this note configures the SmartFusion2 as a WiFi access point (AP), allowing other wireless devices, such as a notebook or smartphone, to connect to the SmartFusion2 using WiFi without any additional equipment. This capability makes it very easy to access a standalone SmartFusion2-based device over TCP/IP, for instance, for checking the device status or offloading collected data for further processing.

Note that this application note is not applicable to the M2S050-FG484 SOM since the M2S050 SmartFusion2 device does not support USB at this time.


Hardware Platform

The hardware platform is Emcraft Systems' M2S-FG484 system-on-module (SOM) plugged into the SOM-BSB-EXT baseboard. The Cortex-M3 core is configured to run at 142 MHz. The on-chip cache is enabled by software for LPDDR.

The demo documented in this application note assumes that the Mini-B to USB 2.0 A Female cable is plugged into the USB OTG interface connector on the SOM-BSB-EXT baseboard and that the USB Wireless adapter (Comfast WU815N) is plugged into the USB 2.0 A Female connector of the above cable.

Note also that to power the M2S-FG484 Starter Kit for this demo, you should plug the mini-USB Y-cable into the P1 mini-USB connector on the SOM-BSB-EXT board and then connect both links of the Y-cable into free USB ports on your PC. This is needed since this demo requires more than 500 mA for reliable operation.


Initial Configuration

Please see this link for instructions on how to configure the M2S-FG484 Starter Kit and the development host for running this demo.


Installing the Demo

The procedure described here explains how to install the bootable Linux image (usbwifi.uImage) to the target.

Here is how you can build and install the bootable Linux image from the project sources (usbwifi.tgz), having installed them on top of the Emcraft Systems SmartFusion2 uClinux distribution.

Note: The Linux image and the sample project have been built and validated in context of the Emcraft Systems Release 1.14.3. If you are using a different release, some porting changes may be needed.


Starting the WiFi Access Point

On power-up reset, U-Boot loads the Linux image from the SPI Flash to the LPDDR and passes control to the kernel entry point:

U-Boot 2010.03-cortexm-1.14.3 (Nov 04 2015 - 13:06:17)

CPU : SmartFusion2 SoC (Cortex-M3 Hard IP)
Freqs: CORTEX-M3=142MHz,PCLK0=71MHz,PCLK1=71MHz
Board: M2S-FG484-SOM Rev 1A, www.emcraft.com
DRAM: 64 MB
In: serial
Out: serial
Err: serial
Net: M2S_MAC
Hit any key to stop autoboot: 0
16384 KiB S25FL128S_64K at 0:0 is now current device
## Booting kernel from Legacy Image at a0007fc0 ...
Image Name: Linux-2.6.33-arm1
Image Type: ARM Linux Kernel Image (uncompressed)
Data Size: 3601568 Bytes = 3.4 MB
Load Address: a0008000
Entry Point: a0008001
Verifying Checksum ... OK
Loading Kernel Image ... OK
OK

Starting kernel ...

The kernel proceeds to boot-up, initializing the configured I/O interfaces and sub-systems:

Linux version 2.6.33-arm1 (psl @ocean.emcraft.com) (gcc version 4.4.1 (Sourcery G++ Lite 2010q1-189) ) #13 Thu Nov 12 20:56:16 MSK 2015
CPU: ARMv7-M Processor [412fc231] revision 1 (ARMv7M)
CPU: NO data cache, 8K instruction cache
Machine: Actel M2S
Built 1 zonelists in Zone order, mobility grouping on. Total pages: 16256
Kernel command line: m2s_platform=m2s-fg484-som console=ttyS0,115200 panic=10
ip=172.17.4.219:172.17.0.1:::m2s-fg484-som:eth0:off ethaddr=C0:B1:3C:83:83:83
PID hash table entries: 256 (order: -2, 1024 bytes)
Dentry cache hash table entries: 8192 (order: 3, 32768 bytes)
Inode-cache hash table entries: 4096 (order: 2, 16384 bytes)
Memory: 64MB = 64MB total
Memory: 61400k/61400k available, 4136k reserved, 0K highmem
Virtual kernel memory layout:
vector : 0x00000000 - 0x00001000 ( 4 kB)
fixmap : 0xfff00000 - 0xfffe0000 ( 896 kB)
vmalloc : 0x00000000 - 0xffffffff (4095 MB)
lowmem : 0xa0000000 - 0xa4000000 ( 64 MB)
modules : 0xa0000000 - 0x01000000 (1552 MB)
.init : 0xa0008000 - 0xa0237000 (2236 kB)
.text : 0xa03195e0 - 0xa0360000 ( 283 kB)
.data : 0xa0360000 - 0xa03774a0 ( 94 kB)
Hierarchical RCU implementation.
NR_IRQS:83
Calibrating delay loop... 132.30 BogoMIPS (lpj=661504)
Mount-cache hash table entries: 512
NET: Registered protocol family 16
usbcore: registered new interface driver usbfs
usbcore: registered new interface driver hub
usbcore: registered new device driver usb
Switching to clocksource mss_timer2

The USB controller is initialized:

musb_hdrc: version 6.0, musb-dma, host, debug=0
musb_hdrc: USB Host mode controller at 40043000 using DMA, IRQ 20
musb_hdrc musb_hdrc: MUSB HDRC host driver
musb_hdrc musb_hdrc: new USB bus registered, assigned bus number 1
usb usb1: New USB device found, idVendor=1d6b, idProduct=0002
usb usb1: New USB device strings: Mfr=3, Product=2, SerialNumber=1
usb usb1: Product: MUSB HDRC host driver
usb usb1: Manufacturer: Linux 2.6.33-arm1 musb-hcd
usb usb1: SerialNumber: musb_hdrc
hub 1-0:1.0: USB hub found
hub 1-0:1.0: 1 port detected
NET: Registered protocol family 2
IP route cache hash table entries: 1024 (order: 0, 4096 bytes)
TCP established hash table entries: 2048 (order: 2, 16384 bytes)
TCP bind hash table entries: 2048 (order: 1, 8192 bytes)
TCP: Hash tables configured (established 2048 bind 2048)
TCP reno registered
RPC: Registered udp transport module.
RPC: Registered tcp transport module.
RPC: Registered tcp NFSv4.1 backchannel transport module.
alg: No test for stdrng (krng)
Serial: 8250/16550 driver, 2 ports, IRQ sharing disabled
serial8250.0: ttyS0 at MMIO 0x40000000 (irq = 10) is a 16550A
console [ttyS0] enabled
serial8250.1: ttyS1 at MMIO 0x40010000 (irq = 11) is a 16550A
Found M2S MAC at 0x40041000, irq 12
m2s_mac_hw_init: MDC set to 5928571Hz (min) instead 2500000Hz
m2f MII bus: probed
found PHY id 0x221556 addr 0
TCP cubic registered
NET: Registered protocol family 17

The USB WiFi module is initialized by the USB controller:

usb 1-1: new high speed USB device using musb_hdrc and address 2
...
usb 1-1: New USB device found, idVendor=148f, idProduct=5370
usb 1-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
usb 1-1: Product: 802.11 n WLAN
usb 1-1: Manufacturer: Ralink
usb 1-1: SerialNumber: 1.0

The startup script /etc/rc loads the required kernel modules for the WiFi support:

loading modules...
compat
Compat-wireless backport release: compat-wireless-v3.4-rc3-1
Backport based on linux-stable.git v3.4-rc3
cfg80211
cfg80211: Calling CRDA to update world regulatory domain
mac80211
rt2x00lib
rt2x00usb
rt2800lib
rt2800usb
usbcore: registered new interface driver rt2800usb
~ #

The script below implements the needed actions to start the WiFi access point:

~ # cat start_ap
#!/bin/sh

echo "Starting AP"
ifconfig wlan0 192.168.1.1 up
ifconfig wlan0
hostapd /etc/hostapd-minimal.conf &
echo "Starting DHCP server"
udhcpd -f /etc/udhcpd.conf &
~ #

The script enables the wlan0 WiFi interface, then starts the user-space daemon implementing access point functionality. The daemon configuration file, /etc/hostapd-minimal.conf, has a minimal configuration to implement a no-encryption access point named SmartFusion2:

~ # cat /etc/hostapd-minimal.conf
#change wlan0 to your wireless device
interface=wlan0
driver=nl80211
ssid=smartfusion2
hw_mode=g
max_num_sta=255
channel=2
~ #

The last line in the above script starts the DHCP daemon, providing network auto-configuration for connected clients. The DHCP daemon is configured to assign an address from the 192.168.1.2 - 192.168.1.255 range to the WiFi client.

Let's start the access point by running the script:

~ # ./start_ap
Starting AP
rt2800usb 1-1:1.0: firmware: using built-in firmware rt2870.bin
wlan0 Link encap:Ethernet HWaddr 00:0F:12:44:0C:5D
inet addr:192.168.1.1 Bcast:192.168.1.255 Mask:255.255.255.0
UP BROADCAST MULTICAST MTU:1500 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)

Starting DHCP server
udhcpd (v1.17.0) started
Configuration file: /etc/hostapd-minimal.conf
Using interface wlan0 with hwaddr 00:0f:12:44:0c:5d and ssid 'smartfusion2'
~ #

At this point, the access point is ready to accept requests for connection. Using a WiFi-connected notebook or smartphone, scan for available wireless networks and connect to the smartfusion2 network:

While connecting, you should see the progress on the SmartFusion2 console:

wlan0: STA e4:ce:8f:3f:bd:b4 IEEE 802.11: authenticated
wlan0: STA e4:ce:8f:3f:bd:b4 IEEE 802.11: associated (aid 1)
wlan0: AP-STA-CONNECTED e4:ce:8f:3f:bd:b4
Sending OFFER of 192.168.1.2
Sending OFFER of 192.168.1.2
Sending ACK to 192.168.1.2

At this point, the SmartFusion2 is connected to the notebook (or smartphone) over TCP/IP. Let's start the HTTP daemon with a demo webpage on the SmartFusion2:

~ # httpd -h /httpd/html
~ #

On the notebook, open http://192.168.1.1 in the browser and observe the page generated by SmartFusion2:


How Fast is TCP/IP on SmartFusion2 using USB WiFi?

As a very rough estimate for the TCP performance of SmartFusion2 using USB WiFi here is the output of an FTP get command transferring a file from a host in a local network to SmartFusion2:

~ # mount -o nolock 192.168.1.3:/home/psl /mnt
~ # time wget ftp://192.168.1.3/pub/test.dat
Connecting to 192.168.1.3 (192.168.1.3:21)
test.dat 100% |*******************************| 9380k --:--:-- ETA
real   0m   13.53s
user   0m   0.59s
sys    0m   5.65s
~ #

Processing the above results, we get the following TCP performance figure: 9380KB/10.74 = 873.37 KB/sec.

As an estimate of the UDP performance, here is the output of a copy command transferring the same file from an NFS-host to the SmartFusion2:

~ # time cp /mnt/test.dat /
real   0m   9.68s
user   0m   0.00s
sys    0m   1.26s
~ #

The UDP performance is 9380KB/7.55=1242.38 KB/sec.

The WiFi connection rate (as reported in the connection status) was 54 Mb/sec in the above test.