Need three SPI master interfaces

RE: Need three SPI master interfaces

Steven Grunza — Tue, 24 Jul 2018 13:32:57 GMT

Using a single SPI controller will prevent the DMA from moving data from the two slaves simultaneously. My hope is that while the nRF52832 CPU is busy handling BLE protocol the DMA will be moving data from the two slaves with the DMA's arbitrating between themselves to get to the data RAM.

Since the board has already been designed and built, it now needs to be three separate SPI controllers.

RE: Need three SPI master interfaces

Martin Lesund — Tue, 24 Jul 2018 13:25:46 GMT

Hi Steven,

You can have one master and several slave. Just have to use the SS (Slave Select) pins to control which one should be active. (see figure)

You can use any GPIO pin as MOSI, MISO etc.

SPI Master documentation

> Use the SPI Master Example as reference.

RE: Need three SPI master interfaces

mtsunstrum — Mon, 23 Jul 2018 22:43:32 GMT

OK, so you will have to have some extra code to manage the TWI and SPI that are using the same peripheral ID.

Depending on your use case, that may be a no-brainer, or there could be some run-time challenges.

Otherwise ... good to go.

RE: Need three SPI master interfaces

Steven Grunza — Mon, 23 Jul 2018 21:56:42 GMT

The board was designed with four pins dedicated to each SPI slave device. There are now TWI/I2C devices on the board. The main purpose of this board is to move data between the SPI ports and a device at the other end of the BLE link.

RE: Need three SPI master interfaces

mtsunstrum — Mon, 23 Jul 2018 21:47:50 GMT

Yes, that is correct, but important to know the limitations of that approach.

= ===================================================

From nRF52 User Manual ...

15.2 Peripherals with shared ID
In general, and with the exception of ID 0, peripherals sharing an ID and base address may not be used
simultaneously. The user can only enable one at the time on this specific ID.

= ===================================================

ID 3 and 4 are common IDs between TWI and SPIM, so if your system is also using TWI, you may not be able to use all 3 the SPIM instances.

= ===================================================

In addition, each of your individual SPIM instances will (most likely) need to use unique pins for SPIM CLK, MISO, MOSI, SS-

It is my understanding that each SPIM instance software driver cannot share pins. ... But I could be wrong here ... just haven't tried that.

So with this approach, for 3 SPI slave devices, you may occupy up to 12 GPIO pins ... which may not be desirable, depending on the number of GPIOs available.

RE: Need three SPI master interfaces

Steven Grunza — Mon, 23 Jul 2018 20:42:45 GMT

Why would I need to reconfigure the SPIM for each different device.

Aren't there three SPI controllers in the nRF52832: SPIM0 (ID 3), SPIM1 (ID 4), and SPIM2 (ID 35)?

RE: Need three SPI master interfaces

mtsunstrum — Mon, 23 Jul 2018 19:50:09 GMT

You cannot configure this within sdk_config.h

Your best option is to configure at run-time, and reconfigure the SPIM at each time that you want to communicate with a selected SPI slave device

nrfx_spim_config_t spim_config = NRFX_SPIM_DEFAULT_CONFIG;
// Above sets default SPIM (SPI Master) configuration settings, with NO SPI pin assignments
spim_config.ss_pin = your slave select pin (1 of your 3 choices);
spim_config.miso_pin = your miso pin;
spim_config.mosi_pin = your mosi pin;
spim_config.sck_pin = your spi clock pin;
spim_config.ss_active_high = false;

// Initializes and enables spim ...
err_code = nrfx_spim_init(&spim, &spim_config, spim_evt_handler, NULL);

//... now proceed to do your SPI Master transfer to your selected SPI slave device
// You would have to do a nrfx_spim_uninit() when you change SPI slave devices

Also note, if each SPI slave supports different clock rates, data phases, etc ... then you would config differently at above configuration stage.