netpp node [Spartan6-LX9]
I am glad to announce a new user evaluation platform module called ‘netpp node’. Its motto is ‘IoT on FPGA done right’:
- Integrated high speed UDP stack for maximum possible bandwidth over 100Mbit Ethernet
- dagobert network SoC with various configureable interfaces (SPI, UART, PWM, I2C) and pin multiplexing options.
- SDK: GCC, GDB hardware debugger
- Up to 5 analog I/O channels with ‘analog population option’
- Piggy backs onto a custom I/O PCB using two 2×16 pin headers
The default firmware runs a fully functional netpp stack for remote control and measurement.
Its main applications:
- Reliable computing (safety relevant applications with tamper-safe main loop watchdogs)
- Guaranteed real-time response in network for scaleable applications (100s of units). Performance outlines:
- Up to 700 netpp continuous property requests per second verified
- Push-on-Demand streaming of arbitrary dataports (high speed ADC) at maximum network bandwidth (10 MByte/s)
- Simple DSP applications and smart analog measurement (low power, filtering and differential options)
- Evaluation of next generation ZPU architecture for embedded GNU style developers
First prototypes are finished and are running 24/7 in the test bench at this moment.
Things are going very smooth so far, just a minor capacitor change will be required for the v0.1 series.
As the full model of this design is available for simulation, we can verify the system effectively against stress situations. In particular, network safety is of outmost importance. The test procedure check list of the dagobert SoC:
- ARP and ping flooding
- netpp packet performance test
- Broken packet handling
- Jumbo packet flooding
- Lost interrupt scenario (packet queue desynchronization)
Monitoring netpp packet performance
Packet behaviour in a real network is measured using the Wireshark protocol analyzer.
The figure below shows some example netpp transaction log that the netpp node handles at a very low CPU overhead based on direct register accesses.The red bars is the effective number of query responses using somewhat ineffective ping-pong requests. The performance can be increased by accumulating data into larger buffer properties.
For i2c or SPI transactions however, the packet rate is expected way lower.
For high speed performance like MJPEG video streaming, a separate UDP/RTP queue can be set up within the firmware to reach maximum throughput. However, there is no handshaking using this method.
The image below shows a repeated property query from within Python. The pauses are introduced by external disturbance (stress test) that causes a packet drop – and the netpp engine to timeout and re-synchronize.
Improved RX/TX queue
With an improved packet FIFO on FPGA, I was able to crank up the number of netpp requests per second, as shown in the Wireshark trace below. This test makes sure that several netpp clients can poll the netpp node at high frequencies without disturbing each other. The blue trace is a repeated poll of the full property tree, the red bars are the timed queries from a process viewer daemon. With no other disturbance, we get the occasional drops (e.g. at 45s, 101.5s) due to the queue running full
- netpp node fact sheet [ PDF: main-netpp-node ]