DMA access using SCI.UART in RA4M1 series controller.

Question

Hi All, 
 
 I am trying to use DMA with UART in RA4M1 series controller, in a custom board. FSP v1.1.0. 
 I got few questions... 
 1. Can we use DMA along with SCI.UART? 
 I have tried to transfer a set of characters, likewise "Hello" through DMA. 
 I have assigned SCI9.TDR address as destination address for DMA. 
 Mode : Normal 
 Transfer Size : 1 
 Number of Transfers : 5 
 I have used a callback, to indicate end of DMA transfer. But I didn't get any callback in here. 
 Then i've tried transfering only one character. 
 Mode : Normal 
 Transfer Size : 1 
 Number of Transfers : 1. 
 This time callback is generated. 
 What's happening in here? Why no DMA callback in case of 5 transfer and why at one transfer? 
 I havent found any success while using other modes of DMA. 
 Bottom line : can we use DMA with uart in RA4M1 series controller?

Richard · Accepted Answer

Hello viswa, 
 EK_RA6M2_SCI_DMAC.zip 
 Please find attached a project that shows how to use the DMAC with UART. (FSP1.3.0, e2studio 2020-07) 
 
 Please note that this is written and tested for a RA6M2 device as I do not have immediate access to a RA4M1. However, you will be able to port this over. 
 
 As Warren mentioned in an earlier post, the DMA is not directly supported when you add a UART stack; on the DTC is. 
 However, it is possible by adding additional DMAC transfer drivers. 
 In this example I use the DMA to perform data transmission and reception 
 
 Configure the DMA transfer drivers are required, for example: 
 
 When you run the code, the data string "Test Data String" will be transmitted twice. The first time is via the CPU and interrupts, the second time is via the DMAC and interrupts. 
 The key to getting the DMA to trigger is to disable the interrupts in the ICU interrupt enable register. If you do not do this then their is contention between the CPU and the DMA, and you do not get the behviour you expect. 
 I hope the code and comments in hal_entry.c explain this. 
 Regards, Richard

Richard · Answer

Hi, 
 
 Please find attached an update. 
 3482.EK_RA4M1_SCI_DMAC.zip 
 This project will address the issue of not being able to switch between using the DMAC and CPU. 
 You will see in the while(1) loop, the application will send 10 continuous data strings (on SCI0) via DMAC and then via the CPU. 
 This process is repeated every time you press the SW1 button on the EK-RA4M1 board 
 You will see that when a switch between DMAC and CPU is required (and vice-versa) we have to set / clear the IELSR (ICU Event Link Setting Register) and DELSR (DMAC Event Link Setting Register) accordingly 
 Hope this helps 
 Regards, 
 Richard