---
user/bsps/arm/imxrt.rst | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/user/bsps/arm/imxrt.rst b/user/bsps/arm/imxrt.rst
index ad18766..6554b3b 100644
--- a/user/bsps/arm/imxrt.rst
+++ b/user/bsps/arm/imxrt.rst
@@ -198,6 +198,28 @@ Note that the SPI-pins on the evaluation board are shared
with the SD card.
Populate R278, R279, R280, R281 on the IMXRT1050-EVKB (Rev A) to use the SPI
pins on the Arduino connector.
+By default, the native chip selects are used. If you want to use GPIOs as chip
+select instead, you can use the `cs-gpios` and `num-cs` attributes just like on
+a Linux SPI controller. A maximum of `IMXRT_LPSPI_MAX_CS` pins can be used.
+
+The hardware doesn't support selecting no native chip select during a transfer.
+Therefore one native chip select has to be reserved as a dummy if you want to
be
+able to use GPIOs. The pin function for this chip select must not be configured
+on any pin. Dummy will be the first of the first four chip selects that is not
a
+native one. Example configuration::
+
+ &lpspi4 {
+ status = "okay";
+ pinctrl-0 = <&my_pinctrl_lpspi4>;
+ cs-gpios = <0>, <0>, <&gpio1 1 0>, <0>, <&gpio11 5 1>;
+ num-cs = <5>;
+ }
+
+In this case, CS2 will be the dummy chip select and no pin must be configured
+with that function. CS0, CS1 and CS3 are just native chip selects and should be
+used via pin functions. GPIO1.1 is used as a high active CS and GPIO11.5 a low
+active one.
+
Limitations:
* Only a basic SPI driver is implemented. This is mostly a driver limitation
and
--
2.35.3
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