Re: WINC1500 Denies FW
The failure of nm_spi_init() usually means a firmware mismatch. The module firmware is only compatible with a range of host driver versions. Look at the documentation and check to see if your host driver is in the correct range.
When re-flash the module firmware over the UART connection, we only use Tx/Rx, no RTS/CTS, needed. I do not know where that info came from.