jbentham
commented
3 years ago I think you're on the right lines, and can't think of anything specific to suggest, but in my experience continuous data streaming is remarkably difficult to achieve - not just obtaining the data, but also doing something useful with it, before the buffers overflow.
As an alternative to ping-pong buffers, you could just use a single buffer, and monitor the current DMA address to detect when there is a block of data to process. I haven't got around to testing this, to see if it makes matters better or worse. However if you want a buffer size over 64K you must use a non-LITE DMA channel, see the 'DMA LITE Engines' topic in the 'BCM2835 ARM Peripherals' document.
I'd question whether your target of 2.5 MS/s will be achievable in practice, and would start with a much lower figure, then see how high it can be pushed before things start to go wrong.
Jeremy Bentham
On 25/06/2021 20:40, BryceDrechselSmith wrote:
Hello, I commented in your streaming code, but i realize that this is the more appropriate folder to comment in. I have successfully gotten this code (rpi_adc_dma_test.c) to capture at 2.5Msamples/sec and store into a .csv file. I am now trying to make this continuously stream the data into a FiFo, similar to your other code in "streaming." I am trying to accomplish this by implementing a ping-pong buffer in the function "adc_dam_samples_ads7884" (line 325), but have had no real luck thus far. This is my first experience with DMA, and as such I am not really familiar with what must be done to set this up. My assumption is that I will need to double the number of control blocks and add another buffer (B), so that while A is being written, B can be read and visa-versa. In looking at your streaming code (rpi_adc_stream.c) for the MCP3008 as a guide, it looks like this is what you are doing in "adc_dma_init" (lines 403+); using several control blocks to write to rxd1, and then several more to write to rxd2, with a few other control blocks used for timing. Since the ADS7884 doesn't take input and is controlled purely by clock cycles, I believe that the timing blocks are unnecessary (that I don't need a third channel for triggering PWM?) though I do need a way to switch between the two. Currently it looks like it is continuously reading from the buffer until it is empty (dma_wait(DMA_CHAN_A)). But I don't think that this method will work for continuous streaming...
I guess my questions are; are my above assumptions correct? what would you recommend in terms of timing/coordinating for the ping-pong buffer?
Once again, thank you so much for your time. I really appreciate the time you have taken already to write this code and its corresponding guide, as well as the time to respond to my previous questions.
Cheers, Bryce
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Hello, I commented in your streaming code, but i realize that this is the more appropriate folder to comment in. I have successfully gotten this code (rpi_adc_dma_test.c) to capture at 2.5Msamples/sec and store into a .csv file. I am now trying to make this continuously stream the data into a FiFo, similar to your other code in "streaming." I am trying to accomplish this by implementing a ping-pong buffer in the function "adc_dma_samples_ads7884" (line 325), but have had no real luck thus far. This is my first experience with DMA, and as such I am not really familiar with what must be done to set this up. My assumption is that I will need to double the number of control blocks and add another buffer (B), so that while A is being written, B can be read and visa-versa. In looking at your streaming code (rpi_adc_stream.c) for the MCP3008 as a guide, it looks like this is what you are doing in "adc_dma_init" (lines 403+); using several control blocks to write to rxd1, and then several more to write to rxd2, with a few other control blocks used for timing. Since the ADS7884 doesn't take input and is controlled purely by clock cycles, I believe that the timing blocks are unnecessary (that I don't need a third channel for triggering PWM?) though I do need a way to switch between the two. Currently it looks like it is continuously reading from the buffer until it is empty (dma_wait(DMA_CHAN_A)). But I don't think that this method will work for continuous streaming...
I guess my questions are; are my above assumptions correct? what would you recommend in terms of timing/coordinating for the ping-pong buffer?
Once again, thank you so much for your time. I really appreciate the time you have taken already to write this code and its corresponding guide, as well as the time to respond to my previous questions.
Cheers, Bryce