Further improve of SD-card performance

RE: Further improve of SD-card performance

Simon — Fri, 09 Jul 2021 12:25:31 GMT

I asked internally and got the following reply:

"SPI frequency issue after SD card initialisation is fixed in NCS 1.6 / Zephyr-2.6 by https://github.com/zephyrproject-rtos/zephyr/pull/33684. FATFS is a block filesystem designed for block devices, like SD card, so I can not follow the problem with that. SDMMC controller driver over SPI is kind of software controller and performance depends direct on SPI controller and CPU perfomance."

RE: Further improve of SD-card performance

Simon — Fri, 09 Jul 2021 11:57:21 GMT

Sorry for the delay on this, a huge part of the support team is on vacation and you may expect delays.

I do not have too much knowledge about this topic. Since it's related to Zephyr, could you ask in any of these places https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.5.1/zephyr/guides/getting-help.html#asking-for-help?

If you find a solution, could you share it here? So other people can benefit?

If you don't get any answers, please get back to me.

RE: Further improve of SD-card performance

flge — Thu, 01 Jul 2021 10:01:48 GMT

Hi Simon,

the nrf_gpio_cfg() function worked very well. I was able to increase the waveform performance dramatically. I've done this with all the pins controlled by the nRF9160. Following the results of the spi-clk pin for example before and after the configuration.

About the SD-protocol. I rerun the zephyr sample for SDHC access (fat_fs in subsys) with the same results in my post above. I've included the thread-analyzer to have an overview about the running threads. Afterwards i increased the main-thread priority, where i'm reading a testfile from the SDHC, always with the same result. It seems that in the driver for the SDHC, the data gets readed in batches (sdhc_spi_rx_block()), so this approach goes nowhere. Is there something in planning to improve the SD-driver? Otherwise i have to try this myself.

Best regards,

RE: Further improve of SD-card performance

flge — Mon, 21 Jun 2021 15:47:05 GMT

Thank you very much for the answer. I will try out your tips and give a feedback when i'm done.

RE: Further improve of SD-card performance

Simon — Mon, 14 Jun 2021 11:45:50 GMT

I'm sorry for the late reply.

[quote user="flge"]Since i'm using the highest possible clock-frequency on the nRF9160, i tried to find out how to configure this option, but i wasn't able to find out how. Can you give me a hint on this one?[/quote]

Check out this answer for how to do this: https://devzone.nordicsemi.com/f/nordic-q-a/64647/spi-not-operating-correctly-at-high-speeds/264121#264121

You can use the Nordic nrf functions (#include <hal/nrf_gpio.h>) directly and set it using nrf_gpio_cfg() like in the link above.

You can also achieve this using the Zephyr layer, just make sure the following gets triggered: https://github.com/nrfconnect/sdk-zephyr/blob/v2.4.99-ncs2/drivers/gpio/gpio_nrfx.c#L155. I think you can do that by running gpio_config() (#include <drivers/gpio.h>) with flags = GPIO_DS_ALT_LOW | GPIO_DS_ALT_HIGH.

[quote user="flge"]To ensure the reading sequence isn't blocked by network-threads, i tested the reading-command also with the networking and webserver disabled, both the same. From the timing perspective there seems to be quiet some potential to save time.[/quote]

Have you gotten any progress on this?

Maybe a solution would be to increase the priority of the thread responsible for the SPI transfer?

RE: Further improve of SD-card performance

flge — Sun, 06 Jun 2021 14:23:14 GMT

Hey Simon, thanks for your reply.

I hooked up up my scope to measure the SPI-lines. This raised question about SPI-pin configuration. As you can see in the image below, the clock frequency is about 8MHz.

The datasheet of the nRF9160 states, that the pins need to be configured as "High Drive" at high bit rates (footnote 10).

Since i'm using the highest possible clock-frequency on the nRF9160, i tried to find out how to configure this option, but i wasn't able to find out how. Can you give me a hint on this one? On the other side the data-line looks well. I think it is possible that this is due to other input-capacitance on this line (SCK --> P0.19 / MISO --> P0.18) of the nRF9160DK Rev. 1.0.0.

When reading a file in chunks of 1024 bytes, we can see the reading-command followed by two blocks of 512 byte data.

Each of these blocks contain eight 64-bytes subs.

Each of these subs contain eight 64-bit bitfields.

Each bitfiled contains 64-bit data.

To ensure the reading sequence isn't blocked by network-threads, i tested the reading-command also with the networking and webserver disabled, both the same. From the timing perspective there seems to be quiet some potential to save time.

Thanks for any help.

RE: Further improve of SD-card performance

Simon — Thu, 03 Jun 2021 13:04:17 GMT

Are you able to attach a logic analyzer to the lines to see what's actually going on and what the speed is.

Best regards,

Simon