In porting the udma_demo example for the EK-TM4C123GXL to the EK-TM4C1294XL Connected LaunchPad, I had a difficult time getting the UART DMA operation to work. Enabling the UART pins to see the UART traffic showed the first block of the UART traffic was sent when the UART DMA was enabled, but the DMA-related UART interrupt was never generated to process additional UART DMA traffic.
After studying the TM4C123 and TM4C1294 datasheets and the application note SPMA065 (Differences Between Tiva C Series TM4C Microcontrollers), it became apparent that the DMA-related interrupts operate differently on the TM4C1294 peripherals (although the associated UART info in SPMA065 was not very helpful and even somewhat misleading).
To get the UART DMA transfers to work, I had to add the following before line 473 in udma_demo.c:
ROM_UARTIntEnable(UART1_BASE, UART_INT_DMARX);
Then enable the interrupts for the UART: (original line 473)
ROM_IntEnable(INT_UART1);
NOTE: The TivaWare Peripheral Driver Library (revision 2.0.1.11577) does *not* document the UART_INT_DMARX interrupt flag (in UARTIntEnable()) or the UART_INT_DMARX or UART_INT_EOT UART interrupt flags either (actually, the UART_INT_EOT is missing from uart.h in the TivaWare source files).
After the above changes (and other TM4C1294-specific initialization changes), I get the following output on the Connected LaunchPad for the udma_demo example:
uDMA Example
Tiva C Series @ 120 MHz
CPU Memory UART Remaining
Usage Transfers Transfers Time
5% 99.3 MB/s 23.0 KB/s 1s
Stopped
Hopefully, this information will be helpful to anyone else trying to use UART (or any other peripheral) DMA on the TM4C129x MCU. The use of DMA on the Tiva MCUs could use an application note on the subject with better and more expanded example code using TivaWare!
