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I've tested BLE Stack 1.3 and unfortunately the problem still persists. Bytes get lost during UART RX ISR and the entire chip has a tendency to lock up when BLE data and UART data are being sent at the same time.
Aslak, could you explain how to enable the option to keep the cpu core running while the radio is operation?
I found in hci_tl.h the following, but I am not using the device in hci mode
HCI_EXT_HALT_DURING_RF_EVENT 0x0419
I also found the NPI layer, but the npi_uart and npi_spi.c files are missing from the Stack 1.3 distribution.