[Answered] SPI: Meaning of some of the pins for spi_bus_config_t

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kolban
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[Answered] SPI: Meaning of some of the pins for spi_bus_config_t

Postby kolban » Tue Jan 10, 2017 5:24 am

Studying the SPI master driver, I find that we must configure a data structure called "spi_bus_config_t". Reading the documentation on it found here:

http://esp-idf.readthedocs.io/en/latest ... s_config_t

I find 5 pins need be configured:

  • spid_io_num
  • spiq_io_num
  • spiclk_io_num
  • spiwp_io_num
  • spihd_io_num

Here comes the list of questions related to these names:

1) What does "spi_d" mean? I understand the SPI concept of "MOSI" ... but the concept of "d" means nothing to me.
2) What does "spi_q" mean? I understand the SPI concept of "MISO" ... but the concept of "q" means nothing to me.
3) What does "spi_wp" mean? I can't relate that to anything I am familiar with in the concept of SPI.
4) What does "spi_hd" mean? I can't relate that to anything I am familiar with in the concept of SPI.
Last edited by kolban on Tue Jan 10, 2017 2:24 pm, edited 1 time in total.
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ESP_Sprite
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Re: SPI: Meaning of some of the pins for spi_bus_config_t

Postby ESP_Sprite » Tue Jan 10, 2017 6:21 am

The SPI flash peripheral actually was initially created to interface with SPI flash chips, which have a d, q, clk, wp and hd pin. I can imagine the SPI port pins are somewhat weird if you aren't familiar with that.

For MISO and MOSI, it is explained in the page you quoted:

int spid_io_num

GPIO pin for spi_d (=MOSI)signal, or -1 if not used.

int spiq_io_num

GPIO pin for spi_q (=MISO) signal, or -1 if not used.



spi_hd is the hold pin pf the flash chip, while spi_wp is for write protect. These pins aren't really used in the 1-bit SPI mode you'd normally use, but the 4-bit mode uses them as data lines.

I agree that the documentation can be slightly better wrt explaining this.

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kolban
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Re: [Answered] SPI: Meaning of some of the pins for spi_bus_config_t

Postby kolban » Fri Jan 13, 2017 3:23 am

For the history ... as of the date of this post, the pins in SPI have been renamed to be:

int mosi_io_num – GPIO for MOSI or -1 if not used.
int miso_io_num – GPIO for MISO or -1 if not used.
int sclk_io_num – GPIO pin for CLK or -1 if not used.
int quadwp_io_num – Specify -1 if not used.
int quadhd_io_num – Specify -1 if not used.
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