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

[kolban]

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.

[ESP_Sprite]

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.

[kolban]

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.