6Mbaud UART with Bus Pirate V4

Question

I would like to sniff data on an SPI bus running at a clock rate of 6 MHz. I would like to use the Bus Pirate V4 for this task. The sniffing itself is supported up to 10 MHz, the problem is getting the data on a PC in real time.

The BP page for the USB connection (V4!) says:

Max speed is 12 Mbps, but a realistic limit is 1 Mbps.

Can I just set the UART speed to 6 Mbps in Windows/Linux?

I have used a 1 Mbit baudrate before, using a 5€ China UART<>USB converter without problems. Since the BP has the USB hardware built-in, I don't see why the realistic limit would be 1 Mbit/s...

Answer 1

About the USB limit.

• Data has to packeted into 'legal' packets according to the USB standard. This adds a couple of bytes to each of them, and lowers the speed.

• In between, the packets have to received at the other end, checked, and confirmed with another packet, still lowering the speed.

• The controller in the sniffer will be quite busy receiving the 'sniffed' info, and thus have less time available to attend to the USB port.

• The USB line is also occupied with short polling packets.

That said, 1Mbps guess is probably just to be safe in all circumstances. However, I doubt that you will get to the 6Mbps (or MHz) of the SPI bus reliably.

Answer 2

Go made an DIY sniffer !

Another issue is "linux is slow on long word size uart" but "windofs is slow on small size uart" communication(ACM-DCM(USB-Base),size=data_length).

Yes you can set 100mbit uart speed but problem is Error ratio !

When used high speed communication device signal down to mV (millivolt) level. Offcourse you can't protect low-level signals ! Speed required buffer memory, you can't handle data on a microsecond(supercomputers can't do either, just ASIC or FPGA can handle this load).