Some performance measurements on the Cosa Telnet Shell and a short update:
1. CosaTelnetShell performance
The test bench is an Arduino Mega 2560, Ethernet Shield and a D-Link DWL-810+ Ethernet Wifi Bridge. Connecting through a Wifi Router and back to a laptop (HP Probook 4540s with Ubuntu 12.04 LTS).
a. Max burst string output
To measure the performance of pure text output from the sketch the command "help" can be used. It will print the command help text. Using the command "repeat 1000 help" will generate a longer period to measure. The measured throughput on the laptop is 60-64 K received bytes per second for this test case (using GNOME Terminal/telnet and PuTTY).
The max performance when filling buffers on the W5100 is 250 KBps (8 MHz SPI, 4 byte command to transfer 1 byte data, 1/4 MBps). This is excluding chip select and all the commands necessary to initiate and check status for the W5100 SEND command.
b. Max analog sample rate
The command "analogread a4" will sample the analog pin a4 and print the value to the io-stream (socket). Again the repeat command can be used to find the upper limit of sampling, converting and sending per second; "repeat -t 2500 analogread a4" will measure the time to execute 2500 analogread. The max rate is between 2000-3000 samples per second (sample values are converted to text, printed to the iostream/socket and sent over Ethernet/Wifi).
The variation is due to other traffic and drops on Wifi but also the sample value as the text conversion time depends on the value. Please note that the max sample rate at 112 us per sample is 8900 samples per seconds. And that the above results is for a pure sequential implementation without interleaving. It is possible to, for instance, run number conversion to text in parallel with the sampling (ADC). This could give as much as 4000-5000 samples (in textual format) per second over Ethernet/Wifi from the Arduino board.
c. New example shell commands
i. Command "pinmode" to get or set the pin mode; input, output and pullup. The command "pinmode all" will print the pin mode for all pins.
ii. The CosaShell/CosaTelenetShell are mainly to demonstrate how to use the Cosa command line support (class Shell) but may also be used as debugging tools; check hardware connections, etc. Two new commands have been added to allow scanning of 1-Wire and I2C (OWI and TWI).
iii. Setting date/time and accessing the Cosa RTC timer. The command "date" may be used to display or set the current date/time.
2. New SPI function; clock()
The new static SPI function clock() will map from frequency to the SPI clock rate setting. This allows device drivers to be written independent of the MCU system clock setting and knowledge of the SPI rate command. A SPI device driver only needs to supply the max frequency required on the bus (for the connected device).
3. Boosting W5100 performance
The W5100 device driver uses the new interleaving SPI API (spi.transfer_start/next/await) so that memory access (load/store) can be executed in parallel with SPI transfers. This gives a performance improvement of 10-20%.
4. Bug fixes
a. Analog mux setting on Mega. Failed to read bandgap correctly after using higher analog pin numbers.
b. Improved W5100::Driver::flush() robustness when client or server disconnects.