Maximum implied Notecard throughput of 1 kB/second?

daterdots · January 27, 2025, 5:21am

I wasn’t sure if GitHub or the forum was the right place for this, so I am cross-posting.

Maximum implied throughput of 1 kB/sec?

opened 05:16AM - 27 Jan 25 UTC

We have a sensor that acquires data at about 4 kB/second, and we have noticed th…at we cannot feed it to the Notecard fast enough to keep up with the pace of data acquisition. We looked into what the fundamental rate limitation is, and it seems like it's ultimately driven by a maximum segment length of 250 bytes combined with an intra-segment delay of 250 ms. Assuming instantaneous i2c or serial transfer to the Notecard, that implies a maximum possible throughput to the Notecard of 1 kB/sec. Is that right? If so, is there anything that we could do to speed this up so that we can keep up with our sensor? https://github.com/blues/note-c/blob/23c2338538d4992dfc2ca9ec51e0a8ceb3d1e071/n_lib.h#L43 https://github.com/blues/note-c/blob/23c2338538d4992dfc2ca9ec51e0a8ceb3d1e071/n_lib.h#L49

We have a sensor that acquires data at about 4 kB/second, and we have noticed that we cannot feed it to the Notecard fast enough to keep up with the pace of data acquisition. We looked into what the fundamental rate limitation is, and it seems like it’s ultimately driven by a maximum segment length of 250 bytes combined with an intra-segment delay of 250 ms. Assuming instantaneous i2c or serial transfer to the Notecard, that implies a maximum possible throughput to the Notecard of 1 kB/sec. Is that right? If so, is there anything that we could do to speed this up so that we can keep up with our sensor?

github.com/blues/note-c

n_lib.h

23c233853


      
          
          // The notecard is a real-time device that has a fixed size interrupt buffer.
          // We can push data at it far, far faster than it can process it, therefore we
          // push it in segments with a pause between each segment.
          
          /**************************************************************************/
          /*!
              @brief  The max length, in bytes, of each request segment when using I2C.
          */
          /**************************************************************************/
          #define CARD_REQUEST_I2C_SEGMENT_MAX_LEN 250
          /**************************************************************************/
          /*!
              @brief  The delay, in miliseconds, of each request when using I2C.
          */
          /**************************************************************************/
          #define CARD_REQUEST_I2C_SEGMENT_DELAY_MS 250
          /**************************************************************************/
          /*!
              @brief  The delay, in miliseconds, between each request chunk when using I2C.
          */

github.com/blues/note-c

n_lib.h

23c233853


      
          /*!
              @brief  The max length, in bytes, of each request segment when using I2C.
          */
          /**************************************************************************/
          #define CARD_REQUEST_I2C_SEGMENT_MAX_LEN 250
          /**************************************************************************/
          /*!
              @brief  The delay, in miliseconds, of each request when using I2C.
          */
          /**************************************************************************/
          #define CARD_REQUEST_I2C_SEGMENT_DELAY_MS 250
          /**************************************************************************/
          /*!
              @brief  The delay, in miliseconds, between each request chunk when using I2C.
          */
          /**************************************************************************/
          #define CARD_REQUEST_I2C_CHUNK_DELAY_MS 20
          /**************************************************************************/
          /*!
              @brief  The delay, in miliseconds, to wait after receiving a NACK I2C.
          */

abucknall · January 31, 2025, 2:40pm

Hi @daterdots,

Could you expand a little on what you’re trying to achieve? The Notecard isn’t designed to stream data like you are suggesting and I think you’ll run into limitations with the size of available flash for notefiles, let alone burning through your API usage allowance. I’ll take a look into note-c and see if I can verify this for you; I want to make you aware of the potential issues with trying to stream data with Notecard.

Thanks,
Alex

daterdots · January 31, 2025, 11:43pm

I am aware of the limitations! We’re not trying to stream data 24/7 from this sensor, but we do notice that we have to buffer the data on our own MCU because the i2c/serial pipe to the Notecard seems to be the rate limiter in the system.

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Maximum implied Notecard throughput of 1 kB/second?

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