SPI MOSI, MISO pins are labelled as TX, RX

[shreekumar3d]

The pinout (Figure 2) shown in the Pico datasheet labels SPI pins as "SPI0/1 TX" and "SPI0/1 RX". In SPI terminology, pins are typically referred to as "SPI MOSI" and "SPI MISO". Can the Pico datasheet be corrected to follow this convention ? This should help reduce confusion & mistakes while connecting SPI devices to the Pico.

This may also help eliminate mistakes when connecting two RP2040s over SPI. With SPI pins labelled as RX/TX, folks who are familiar with UART may end up creating cross-connections (RX -> TX, and TX -> RX).

The RP2040 datasheet - given it's lower level nature - must use MOSI & MISO in the context of SPI. The following places would need corrections:

1. Section 1.4.3, "GPIO functions"
2. Section 2.19.2, "Function Select"
3. Section 2.5.3.1, "System DREQ Table"

Similarly, the C SDK & documentation needs to be modified.

Note that all the PIO programs use the right conventions. So I found some of these deviations surprising in an otherwise admirable documentation effort.

[lurch]

I believe we use the TX / RX nomenclature because when the RP2040 is operating as a master SPI device, then TX is MOSI (Master Out) and RX is MISO; but when the RP2040 is operating as a slave SPI device, then TX is MISO (Slave Out) and RX is MOSI.
So yes, when you're connecting an RP2040 SPI master to an RP2040 SPI slave you would indeed cross-connect RX to TX and vice-versa. (although we don't have any SPI slave example code merged yet, see raspberrypi/pico-examples#101 )