mimxrt: Implement the review comments.

robert-hh · robert-hh · commit a77a47aa75c2 · 2022-09-08T14:23:58.000+02:00
diff --git a/docs/mimxrt/quickref.rst b/docs/mimxrt/quickref.rst
@@ -303,13 +303,16 @@ rates (up to 30Mhz).  Hardware SPI is accessed via the
 
     from machine import SPI, Pin
 
+    spi = SPI(0, 10000000)
     cs_pin = Pin(6, Pin.OUT, value=1)
+    cs_pin(0)
     spi.write('Hello World')
+    cs_pin(1)
 
 For the assignment of Pins to SPI signals, refer to
 :ref:`Hardware SPI pinout <mimxrt_spi_pinout>`.
 The keyword option cs=n can be used to enable the cs pin 0 or 1 for an automatic cs signal. The
-default is cs=0. Using cs=-1 the automatic cs signal is not created. 
+default is cs=-1. Using cs=-1 the automatic cs signal is not created. 
 In that case, cs has to be set by the script. Clearing that assignment requires a power cycle.
 
 Notes:
diff --git a/ports/mimxrt/machine_spi.c b/ports/mimxrt/machine_spi.c
@@ -131,7 +131,7 @@ mp_obj_t machine_spi_make_new(const mp_obj_type_t *type, size_t n_args, size_t n
         { MP_QSTR_firstbit, MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = DEFAULT_SPI_FIRSTBIT} },
         { MP_QSTR_gap_ns,   MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = -1} },
         { MP_QSTR_drive,    MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = DEFAULT_SPI_DRIVE} },
-        { MP_QSTR_cs,       MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = 0} },
+        { MP_QSTR_cs,       MP_ARG_KW_ONLY | MP_ARG_INT, {.u_int = -1} },
     };
 
     // Parse the arguments.
@@ -174,7 +174,9 @@ mp_obj_t machine_spi_make_new(const mp_obj_type_t *type, size_t n_args, size_t n
     self->master_config->lastSckToPcsDelayInNanoSec = self->master_config->betweenTransferDelayInNanoSec;
     self->master_config->pcsToSckDelayInNanoSec = self->master_config->betweenTransferDelayInNanoSec;
     int8_t cs = args[ARG_cs].u_int;
-    // The default value 0 is set already, so only cs=1 has to be set.
+    // In the SPI master_config for automatic CS the value cs=0 is set already,
+    // so only cs=1 has to be addressed here. The case cs == -1 for manual CS is handled
+    // in the function spi_set_iomux() and the value in the master_config can stay at 0.
     if (cs == 1) {
         self->master_config->whichPcs = cs;
     }
