{
    "name": "stm32-emac",
    "config": {
        "eth-rxbufnb": 4,
        "eth-txbufnb": 4
    },
    "target_overrides": {
        "NUCLEO_F207ZG": {
            "eth-rxbufnb": 1,
            "eth-txbufnb": 4
        }
    }
}

{
    "name": "stm32-emac",
    "config": {
        "eth-rxbufnb": 4,
        "eth-txbufnb": 4
    },
    "target_overrides": {
        "NUCLEO_F207ZG": {
            "eth-rxbufnb": 2,
            "eth-txbufnb": 4
        }
    }
}

Fix for NUCLEO_F207 UDPSOCKET_ECHOTEST_BURST_NONBLOCK fails. Increase eth-rxbufnb from 1 to 2 will fix the problem
Fix for NUCLEO_F207 UDPSOCKET_ECHOTEST_BURST_NONBLOCK fails.
Increase eth-rxbufnb from 1 to 2 will fix the problem
