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mSGDMA: Streaming to MM problem


Hi everyone,


Recently, I want to play with mSGDMA and learn about it so just make up my own project to test and see the behaviour and know how to control the mSGDMA. However, I got stuck and have tried everything I know but still cannot fix it.



-HPS with h2f_lw_bridge


  • Streaming to Memory Mapped
  • Data width: 8
  • Data Path FIFO depth: 32
  • Descriptor FIFO depth: 32
  • Maximum transfer length: 1KB
  • Transfer type: Aligned Accesses
  • Everything else is disabled

-My customized counter with streaming interface: I made this component just to test the mSGDMA. The counter increase the value every 1 second and output it in streaming interface. It has:

  • Data width: 8 bits
  • Data bits per symbol: 8 bits

-LED PIO: written by mSGDMA write master with the transfered data and it is supposed to increase every second.



Here is C code:

typedef struct sgdma_descr { uint32_t *read_addr; uint32_t *write_addr; uint32_t length; uint32_t control; }sgdma_descr_t;   int main () { uint32_t status ; /*bridge configuration*/ alt_bridge_init(ALT_BRIDGE_LWH2F,NULL,NULL); alt_bridge_init(ALT_BRIDGE_H2F,NULL,NULL);   sgdma_descr_t descr; sgdma_descr_t *descr_ptr = &descr;   // configure the descriptor for ST to MM transferring descr->read_addr = NULL; descr->write_addr = 0; // address of PIO seen by mSGDMA write master descr->length = 1; descr->control =(1<<31) ; // no setting, just go for one data transfer   // feed the descriptor to the descriptor slave alt_write_word(DESCR_RADDR,descr->read_addr); alt_write_word(DESCR_WADDR,descr->write_addr); alt_write_word(DESCR_LENGTH,descr->length); alt_write_word(DESCR_CONTROL,descr->control);   uint32_t status; while(1) { // observe value inside the registers status = alt_read_word(CSR_STATUS); printf("Status: %u\n",status);   status = alt_read_word(CSR_CONTROL); printf("CONTROL: %u\n",status);   status = alt_read_word(CSR_LEVEL); printf("LEVEL: %u\n",status);   } return 0; }

It states that the mSGDMA is still busy transfering ( Busy bit is set ) and the descriptor buffer is empty ( Descriptor buffer empty bit is set and the value in Write fill level register is 0 ). However, I see nothing is transferred because the LEDs are not lighted up.


I had tried the same test with regular DMA Controller and it worked fine. But with mSGDMA it does not work with my test.


Hope someone can give me a hint how to fix this. Thanks in advance !



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4 Replies

Your command sequence seems good to initiate a DMA transfer. Can you confirm whether streaming data is written correctly into the SGDMA? You may use SignalTap or simulation to check it.


Hi GNg,


Thanks for your response!


I also doubt that my streaming interface is a problem because I work fine with MM-MM. I did check it my streaming interface with Modelsim and also implemented it with Avalon FIFO, it works fine.


Maybe I will test it with SignalTap but I need to learn how to use because I have never used it before 😅 .


One thing also got my attention. At first, my counter's data width is 32 bits and data bits per symbol = 32. I got a warning that the mSGDMA data bits per symbol is only 8, if I want to transfer 32 bits data, I have to configure it to 8 bits data per symbol and 4 symbol per beat. I do not know how to change it to 4 symbol per beat. Whenever I change to 8 data bits per symbol ( with data width is 32 ) in "New Component" configuration window, it only transfer my 8 LSB data[7:0].


Once again, thanks for your answer. I will check on SignalTap when I have time.

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It is pretty straightforward for SignalTap usage. Go through this training https://www.youtube.com/watch?v=DCUhsezqydQ would help. Which interface do you need to change its bits per symbol? source streaming from counter? Refer to avalon-mm spec https://www.intel.com/content/dam/www/programmable/us/en/pdfs/literature/manual/mnl_avalon_spec.pdf, Table 18,pg43, you are able to change its streaming properties using "dataBitsPerSymbol"

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I am trying to implement triple speed ethernet in Cyclone 10 FPGA. I have integrated triple speed ethernet core in platform designer in qsys. If i pump data and do loop back in system side of MAC, its working fine. I am able to monitor Start of packet, data valid, data, End of packet properly in signal tap. Now my aim is that i try to capture the streaming data in system side of MAC directly in Nios side memory. For this i am using Modular Scatter gather DMA. For receive data i am using one MSGDMA in streaming to memory mode and one for transmit data i am using one MSGDMA in  memory to streaming mode. I try to capture data in descriptor memory in onchip ram. But i am not getting any data.

I have doubt about my connections of MSGDMA in Qsys.There are no any specific examples detailing how to use MSGDMA with TSE. Some people have done it with SGDMA . I am using quartus 18.1. So how to go about it. How to capture data in onchip RAM.


Kindly guide



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