SPI not operating correctly at high speeds

RE: SPI not operating correctly at high speeds

hmolesworth — Wed, 12 Aug 2020 15:40:01 GMT

Sorry to be pedantic, but standard drive will not look the same as high drive on your scope, even with significant wire lengths; if it does look the same, then high drive has not been applied correctly. Perhaps review this setting again, the high drive must be set after any SPI init otherwise it will be overwritten by that SPI init.

Also place one channel of the scope on SCK at the Nordic end with the scope Gnd on Nordic Gnd, and place a second scope channel on SCK (same signal) on the remote device end with that second scope Gnd at the Gnd on the remote device end. Capture the trace and post them here. They will not look the same if the scope probes are placed correctly even though they are connected by a 6 inch jumper.

RE: SPI not operating correctly at high speeds

T IJ — Wed, 12 Aug 2020 13:57:02 GMT

This is clock on Pin 8, still the same.

[quote userid="5418" url="~/f/nordic-q-a/64647/spi-not-operating-correctly-at-high-speeds/264284"]On 52832 DK, pin 7 is a CTS signal of debug UART - this may cause an issue.[/quote]

I have turned off the UART debug output in the CMSIS config wizzard. I always use the RTT option.

Pin 11 also looks the same.

RE: SPI not operating correctly at high speeds

Dmitry — Wed, 12 Aug 2020 13:19:40 GMT

On 52832 DK, pin 7 is a CTS signal of debug UART - this may cause an issue.

RE: SPI not operating correctly at high speeds

Simonr — Wed, 12 Aug 2020 12:20:05 GMT

Hi Tom

Seeing as the SCK signal seems to be the source of the problem here, have you tried switching this to be any other GPIO, to make sure that it isn't specific to that one pin (just in case there is any issues with the soldering or connection on that GPIO.

Best regards,

Simon

RE: SPI not operating correctly at high speeds

T IJ — Wed, 12 Aug 2020 05:46:46 GMT

[quote userid="86994" url="~/f/nordic-q-a/64647/spi-not-operating-correctly-at-high-speeds"]I have my pins configured to have high drive.[/quote]

I've done that already.

Tested it with standard drive as well.

It might be due to the wires and everything but in my opinion this shouldn't make that much of a difference.

If my SPI device is located at the other side of my circuit board do I get the same behavior as having it like I have now with the long wires?

I've tried it with a simple Arduino pushing out at 8 MHz to compare to see if the analyzer is the problem but it isn't. The Arduino has proper clocks instead of a sine that the NRF is producing.

RE: SPI not operating correctly at high speeds

hmolesworth — Tue, 11 Aug 2020 16:28:40 GMT

Clock speed is only one consideration; the other is capacitive load on the outputs. Long leads such as these inevitably slow the clock edges and so therefore High Drive is required.

Try this:

#define SPI_MOSI 19
#define SPI_CLK   7
#define SPI_CS   25

// Init first then set High Drive 0 and 1 (something like this):
APP_ERROR_CHECK(nrf_drv_spi_init(&spi, &spi_config, spi_event_handler, NULL));
// Boost drive to MOSI and CLK and CS to sharpen clock edges and timing
nrf_gpio_cfg(SPI_MOSI, NRF_GPIO_PIN_DIR_OUTPUT, NRF_GPIO_PIN_INPUT_CONNECT, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_H0H1, NRF_GPIO_PIN_NOSENSE);
nrf_gpio_cfg(SPI_CLK,  NRF_GPIO_PIN_DIR_OUTPUT, NRF_GPIO_PIN_INPUT_CONNECT, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_H0H1, NRF_GPIO_PIN_NOSENSE);
nrf_gpio_cfg(SPI_CS,   NRF_GPIO_PIN_DIR_OUTPUT, NRF_GPIO_PIN_INPUT_CONNECT, NRF_GPIO_PIN_NOPULL, NRF_GPIO_PIN_H0H1, NRF_GPIO_PIN_NOSENSE);

RE: SPI not operating correctly at high speeds

T IJ — Tue, 11 Aug 2020 13:48:53 GMT

I am testing it like this, without any external device attached to it.

Please tell me its a hardware issue

RE: SPI not operating correctly at high speeds

Simonr — Tue, 11 Aug 2020 13:24:44 GMT

Are you able to reproduce this on a DK, or are you only seeing this on a custom board? If this is specific to a custom board, please check your soldering, as the SCK pin may be connected somewhere it shouldn't be, or the other way around. All the pins you're using should be okay, and if that's the only thing that has changed in your project code, everything points toward this being a HW issue.

Best regards,

Simon

RE: SPI not operating correctly at high speeds

T IJ — Tue, 11 Aug 2020 09:29:42 GMT

I've done some further measurements and found out that the SCK signal isn't looking that good.

This is done using 50Msps analyzer and the Vmin and Vmax are not what I expect them to be.

This is what the data looks like and here the Vmin and Vmax are what I expect them to be.

Anyone got a clue what is going on?

RE: SPI not operating correctly at high speeds

T IJ — Mon, 10 Aug 2020 13:36:21 GMT

I've used the example project and changed the pins to:

spi_config.ss_pin = 25;
spi_config.miso_pin = 11;
spi_config.mosi_pin = 19;
spi_config.sck_pin = 7;

RE: SPI not operating correctly at high speeds

Simonr — Mon, 10 Aug 2020 13:29:12 GMT

Seeing issues at 500kbps already seems very strange, as that doesn't really qualify as "high-speed". What pins exactly are you using for SPI here? Is your project based on one of our example projects? If not, please check one of our SPI example projects, whether you're able to reproduce this issue there as well.

Best regards,

Simon