The drive capacity is not related to IAR, its known for the DK that it has problems with other settings than medium, probably because it has a lot of different features and therefore the routing of the signals is somewhat complex (long traces with stubs) which may not be the best for a 50MHz interface. The drive capacity changes the current delivery capacity from a pin, with this changes the impedance of the source and so it is possible to influence reflections on a transmission line. But on my custom board i have seen problems too: For tests I did with my board i used a .png with 250k and a 1.5M jpg in the webserver and I recognized artifacts in the jpg on 3 different PCs, one with XP and Firefox, one with Windows 10 and Firefox and one with Vista and an older Version of Opera. Strangely the errors in the picture are always on the same positions in the Picture on one PC, a reload changes nothing. But they are on different positions on each PC! They appear not when the pic is opened in a viewer or viewed with the browsers directly from the file. From time to time there where problems with the small logos too, they appeared distorted or missing. I replaced the LAN cable, switched off a DC-Converter nearby the LAN-Interface, tested all possible drive capacitys: No change. The traces of the RMII are short 5-6cm, source terminated with 33Ohm, the clock is separated from the other lines. The phy-chip is very close to the LAN-Connector with magnetics. I have no idea what might cause the errors. BTW: I haven't seen the ETH1_IRQ# connected to P002 on the DK anywhere in the pin configuration, is it used at all?
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