This article describes connecting a WIZnet W5500 Ethernet controller to Sega Dreamcast and NAOMI/NAOMI 2 systems using existing serial interfaces configured for SPI. The W5500 is used in MACRAW mode and provides raw Ethernet frame access. The driver has already been merged into KallistiOS master and will be supported in the next version of DreamShell.
Here are the tests through the network stack when copying a file via FTP:

• SCIF SPI: TX ~1000 KB/s (PIO), RX ~550 KB/s (PIO)
• SCI SPI: TX ~900 KB/s (DMA), RX ~1000 KB/s (partial DMA)

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A simple hardware modification for NAOMI and NAOMI 2 to disconnect the JVS controller from port 0 (port A on the Dreamcast). You just need solder jumper JP3 and switch it. This is a very useful for DreamShell and running Dreamcast games by it.
After this, you can connect all Dreamcast peripherals to port A. This will result in all four ports available on the side board: A, B, C and D.

You need to find it on your revision of motherboard. The jumper pads is present on all NAOMI and NAOMI 2 revisions. Here I will show an example on the most common version of NAOMI:

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This guide explains how to access the SH-4 SCI port on Sega Dreamcast and NAOMI systems in both UART/SPI communication modes. It can be used for debugging or connecting an SD card. In SPI-like mode, the SCI port can transfer data at speeds up to 1.5 MB/s, which is twice as fast as using the SCIF port for bit-bang SPI.

Sega Dreamcast Motherboard

Solder wires directly to the following points on the Dreamcast motherboard:

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