1In this test suite two instances of the SPI peripheral are connected together.
2One SPI instance works as a controller, second one is configured as a peripheral.
3In each test, both instances get identical configuration (CPOL, CPHA, bitrate, etc.).
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5Four GPIO loopbacks are required (see overlay for nrf54l15pdk for reference):
61. spi22-SPIM_SCK connected with spi21-SPIS_SCK,
72. spi22-SPIM_MISO connected with spi21-SPIS_MISO,
83. spi22-SPIM_MOSI connected with spi21-SPIS_MOSI,
94. spi22-cs-gpios connected with spi21-SPIS_CSN.
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