RE: nrf51822 TX bytes not back to back at 12K8 or 38K4 baud

John — Wed, 29 Mar 2017 13:49:06 GMT

Without knowing what your application timing requirements for the UART are it's hard to suggest a exact solution. However, I can try to help with your questions:

Is there a TX FIFO? There is no HW FIFO on the nRF51. There is a software TX FIFO implementation if you use the app_uart_put(); function and app_uart_fifo.c and app_fifo.c
Is the easyDMA controller usable for TX? No, easyDMA is not available for the UART on the nRF51, it is on the nRF52 but that doesn't help you much here.
Is there a way to get time in the radio interrupt to copy bytes? Not sure exactly what you need to do here. However, you can use the Radio Notification feature to make sure you can complete your UART work before the radio interrupts you. There is also a time slicing feature of the Soft Device that may be of use depending on what exactly you need here.