reorg

2023-12_ethernet-real-data-rates.md → wiznet_ethernet/2023-12_ethernet-real-data-rates.md

@@ -70,7 +70,7 @@ Things to try would include... taking the Ethernet library offline (into-repo) a
 
 So, for quicksies, and to settle this current debate, I should try not-pinging with this code, just straight up receiving hella UDP upstream...
 
-### Non-Pining Speed Tests 
+### Non-Pinging Speed Tests 
 
 - setup Arduino to, after one packet rx (to get an IP to tx-back-to) just free-form wrips packets up north, and occasionally prints rates to the OLED
 - setup an async (?) version of the python inheritor, and collect them data 
@@ -79,7 +79,19 @@ So... this does improve the rate substantially:
 
 ![oneway](images/2023-12-28_eth-oneway-64.png)
 
-I think actually these are blocking calls, so flow-control down below is as simple as running the thing over-and-over:
+I am seeing on the scope that each transmit takes about 350us, which is reflected in the histogram above... so, while I am also wondering how much of this is to do with the ethernet-to-usb adapter I am using on the laptop side, I am basically convinced that the bottleneck here is the 12MHz SPI. 
+
+However, that would mean we have ~ 10/12 MBits/sec of overhead. But, also looking at the scope, I see significant air gaps between each byte on the SPI line, around 2us per byte - meaning that this is not entirely unlikely (each byte is just 0.8us-ish) so we already have 2/3rds overhead just in those air gaps, and then we have also whatever WIZ-To-Micro overhead to contend with as well. 
+
+So, scope trace: blue arrows highlight the length of one packet-write in embedded, with SPI transactions on CH2 (CS) and CH3 (CLK) - this shows me it's blocking writes, basically, and the width of the write is essentially the same as we measure in the histogram above. 
+
+![spi](images/2023-12-28_ethernet-wiz-spi-01.jpg)
+
+Then we zoom in to see all of these "air gaps" in the SPI CLK line (CH3) - no data is transferred without a CLK pulse, so, this is big overhead loss, and IDK WTF the MCU is doing in these gaps, but it ain't efficient. 
+
+![spi](images/2023-12-28_ethernet-wiz-spi-02.jpg)
+
+This is the relevant CPP and Python... 
 
 ```cpp
 void loop() {