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Explorer
Explorer
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Registered: ‎01-13-2018

S2MM_LENGTH Register in AXI DMA and TLAST in AXI Stream

Hi, 

I am working on a AXI Streaming interface. The custom AXI Stream is a simple counter which has TLAST on every 8th count in TDATA, where TDATA is 32 bit wide. I am wondering how to set S2MM_LENGTH in AXI DMA in simple register mode. This register S2MM_LENGTH define the length of data to transfer. Is this related to TLAST ? 

Should S2MM_LENGTH be 32? because TLAST comes every 8th count which means 8 x 4 = 32 bytes. 

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Explorer
Explorer
565 Views
Registered: ‎01-13-2018

Re: S2MM_LENGTH in AXI DMA configuration ??

Hi, 

I have attached AXI Stream source code which is a simple counter starting from 1 when TVALID and TREADY both high. The helloworld SDK program is also in the folder attach. The TLAST appears on every 8th count in simulation, test bench is also attached. The S2MM_LENGTH is 32 in SDK but there is something strange when I read the DRAM after DMA transfer. Somehow it is working but there is data repetition. The value 6 appear two times in DRAM. 

I don't know where is the bug. In simulation it looks fine. Is this bug related to DMA configuration ? 

Performing the first DMA transfer (main) ... 
The values in DRAM at End of program at address A000000 is 1
 The values in DRAM at End of program at address A000004 is 2
 The values in DRAM at End of program at address A000008 is 3
 The values in DRAM at End of program at address A00000C is 4
 The values in DRAM at End of program at address A000010 is 6
 The values in DRAM at End of program at address A000014 is 6
 The values in DRAM at End of program at address A000018 is 7
 The values in DRAM at End of program at address A00001C is 8
 End of program (main) ... 

 

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Explorer
Explorer
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Registered: ‎01-13-2018

Re: S2MM_LENGTH Register in AXI DMA and TLAST in AXI Stream

@stephenm @kvasantr 

Hi, Any idea about what is special with counter value 6 ? as it appears twice in DMA transfer. 

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