Looking at the information I could find about the new RPi4, it does not technically have full USB 3.0 throughput.
“USB is provided via an external VLI controller, connected over a single PCI Express Gen 2 lane, and providing a total of 4Gbps of bandwidth, shared between the four ports.”
The VLI chip (VL805-Q6) can support PCIe version 2 x16, I’ve seen PCIe x16 cards using this chip that support 4 full speed USB3.0 ports, but at a guess the SoC (BCM2711B0) in the RPi4B can only provide x1.
So anyhow instead of the typical 5Gbps for a single USB 3.0 port there is only 4Gbps shared between all 4 USB ports. I’m curious if anyone has tried a LimeSDR with this, using only one USB 3.0 port (for maximum performance) with nothing else in the other three USB ports.
So far I’ve read that the:
Airspy works, the
HackRF no information yet,
USRP no information yet,
BladeRF 2.0 no information yet,
RTL-SDR dongles, some people have reported that they can not get them to work and only see the following error messages “rtlsdr_read_reg failed with -7” and “rtlsdr_write_reg failed with -7”. But traditionally register read and write errors are associated with low voltage and the latest RPi4B uses a more power than the previous RPi hardware, so it could well just be a power issue.
Baseline (no external hardware connected, no overclocking)
Raspberry Pi 2 B 1.6 watts (idle) to 3.7 watts (stress --cpu 4) Raspberry Pi 3 A+ 1.2 watts (idle) to 5.4 watts (stress --cpu 4) Raspberry Pi 3 B 2.1 watts (idle) to 5.9 watts (stress --cpu 4) Raspberry Pi 3 B+ 2.9 watts (idle) to 6.4 watts (stress --cpu 4) Raspberry Pi 4 B 3.4 watts (idle) to 7.6 watts (stress --cpu 4)
The current recommended RPi4B power supply should output at least 3A@5V which should be enough to also power a LimeSDR (which I would guess would need 4.5 to 5.5 watts).
Anyhow quickly circling back to my original question, do you own a RPi4, if so does it work with the LimeSDR (USB or mini) ?
And with the “USB 3.0 port” (at least 20% lower maximum throughput on the RPi4, if only one device is connected) was there any issues, say running two RX channels at the maximum sample rate (2RX x 61.44MSPS x 2IQ x 12bits / 8bits = 368.64 MB/sec) ?
Any issue if you used a few low traffic devices on the other USB ports at the same time, say a keyboard and a mouse, did that cause any samples to drop.