APP_UART_COMMUNICATION_ERROR after migration from SDK 14.2 to SDK 15.3

[Adam Gordon]

I have been migrating a project from SDK 14.2 to SDK 15.3 and have encountered an issue with UART. I am using the legacy layer with the following configurations:

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#define UART_ENABLED 1

#define UART_DEFAULT_CONFIG_HWFC 0

#define UART_EASY_DMA_SUPPORT 0

#define UART_LEGACY_SUPPORT 1

#define UART0_ENABLED 1

#define UART0_CONFIG_USE_EASY_DMA 0

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#define UART_ENABLED 1

#define UART_DEFAULT_CONFIG_HWFC 0

#define UART_EASY_DMA_SUPPORT 0

#define UART_LEGACY_SUPPORT 1

#define UART0_ENABLED 1

#define UART0_CONFIG_USE_EASY_DMA 0

I am sending and receiving JSON strings and am having no issues with transmitting messages, I am seeing the same behaviour as before the migration. Unfortunately I am running into an issue with receiving messages. What's odd is that I can always successfully receive one message without issue. It is when receiving a second message that I get an APP_UART_COMMUNICATION_ERROR. Every message that follows will also get the same error. After observing this behaviour, I can still transmit messages without issue.

The app_uart_event has a type of APP_UART_COMMUNICATION_ERROR while the data fields of error_communication, error_code, and value are all equal to 1. I read in another thread that that is an overflow error, however my RX buffer is 256 characters, and the message it is receiving is 8 characters long.

I tried flushing after receiving the error using app_uart_flush() but it had no effect. I also tried disabling prs to see if that was the cause but it made no difference.

Any help with the issue or insight would be greatly appreciated.