Investigate slowness

[kaidokert]

With iperf3 client i'm getting quite slow speeds right now, like ~30kb/s

A couple potential culprits:

• Implement DMA transfers on Feather. I think the Arduino version does this

• Clean up and get ( optional ) IRQ feature in [Do not submit] IRQ investigation #34

• Potentially disable CRC - i think default Arduino code leaves it off. Could be a bit of overhead

[kaidokert]

Here's an old discussion thread https://forum.pjrc.com/index.php?threads/teensy-3-6-with-winc1500-on-spi1-is-this-a-good-data-rate.49377/

3+ mbps should be achievable

Also it doesn't appear the Arduino WiFi101 library implements DMA, so this shouldn't be the culprit.

[kaidokert]

Looks like Wifi101 may also not be able to get any faster, previous reports indicate 40-50kb/s: arduino-libraries/WiFi101#176

With this speed test [https://github.com/kaidokert/winc-rs/commit/acb8d37ee91815355400516de8a865d91d8aa42e]

I got these results:

Progress: 9672704 bytes in 160.9 sec | 481.0 Kbps (0.48 Mbps)
Progress: 9733120 bytes in 161.9 sec | 481.0 Kbps (0.48 Mbps)
Progress: 9793536 bytes in 162.9 sec | 481.0 Kbps (0.48 Mbps)
Progress: 9829285 bytes in 164.5 sec | 478.1 Kbps (0.48 Mbps)

=== Download Complete ===
Total bytes: 9829285
Total time: 164.49 seconds

=== Final Results ===
Speed: 59757 bytes/sec (58.4 KB/s, 0.06 MB/s)
Throughput: 478.1 Kbps (0.48 Mbps)

So maybe 50 kilobytes / sec is the actual benchmark to meet.

[kaidokert]

Note current TCP + UDP iperf Rust tests achieve roughly the same. Speed test: 990163f

I'm getting about

[INFO ] Progress: 922 KB received in 9 seconds (speed_test feather/examples/speed_test.rs:189)
[INFO ] Progress: 945 KB received in 9 seconds (speed_test feather/examples/speed_test.rs:189)
[INFO ] Receive ended with: OpFailed(ConnAborted) (speed_test feather/examples/speed_test.rs:200)
[INFO ] === Download Complete === (speed_test feather/examples/speed_test.rs:208)
[INFO ] Total bytes received: 979407 (speed_test feather/examples/speed_test.rs:209)
[INFO ] Total size: 956 KB (0 MB) (speed_test feather/examples/speed_test.rs:214)
[INFO ] Time elapsed: 9 seconds (speed_test feather/examples/speed_test.rs:215)
[INFO ] Average speed: 106 KB/s (speed_test feather/examples/speed_test.rs:216)
[INFO ] Speed calculation requires timer implementation (speed_test feather/examples/speed_test.rs:220)
[INFO ] Compare this total with Arduino results for relative performance (speed_test feather/examples/speed_test.rs:221)
[INFO ] === Speed Test Complete === (speed_test feather/examples/speed_test.rs:75)

[kaidokert]

Okay, Atmel has iperf app note here: https://ww1.microchip.com/downloads/en/Appnotes/ATWINC15x0-Throughput-Measurement-Using-iPerf-Application-Note-DS00002879A.pdf

They claim a lot better results.

[kaidokert]

Okay - SAMD21 PRO runs SPI bus at 12mhz. This crate defaults to 4mhz at the moment - no surprise it's slower. However with a quick test - changing to 8Mhz doesn't make any difference in http download speed.

[kaidokert]

With UDP iperf @ 8Mhz

[INFO ] UDP Speed 102.83797 KB/s (822.70374 Kbits/s)

Thats still about 2x slower than ASF, but not terrible