extmod/machine_spi: Use delay_half, not baudrate, for internal timing.

The delay_half parameter must be specified by the port to set up the
timing of the software SPI.  This allows the port to adjust the timing
value to better suit its timing characteristics, as well as provide a
more accurate printing of the baudrate.

1 files changed, 16 insertions, 3 deletions

diff --git a/stmhal/spi.c b/stmhal/spi.c
index 46da05fac..8ec6f8627 100644
--- a/stmhal/spi.c
+++ b/stmhal/spi.c
@@ -944,10 +944,23 @@ STATIC MP_DEFINE_CONST_DICT(machine_spi_locals_dict, machine_spi_locals_dict_tab
 
 /* code for soft implementation ***********************************************/
 
+STATIC uint32_t baudrate_from_delay_half(uint32_t delay_half) {
+    return 500000 / delay_half;
+}
+
+STATIC uint32_t baudrate_to_delay_half(uint32_t baudrate) {
+    uint32_t delay_half = 500000 / baudrate;
+    // round delay_half up so that: actual_baudrate <= requested_baudrate
+    if (500000 % baudrate != 0) {
+        delay_half += 1;
+    }
+    return delay_half;
+}
+
 STATIC void machine_soft_spi_print(const mp_print_t *print, mp_obj_t self_in, mp_print_kind_t kind) {
     mp_machine_soft_spi_obj_t *self = MP_OBJ_TO_PTR(self_in);
     mp_printf(print, "SPI(-1, baudrate=%u, polarity=%u, phase=%u, sck=%q, mosi=%q, miso=%q)",
-        self->baudrate, self->polarity, self->phase,
+        baudrate_from_delay_half(self->delay_half), self->polarity, self->phase,
         self->sck->name, self->mosi->name, self->miso->name);
 }
 
@@ -957,7 +970,7 @@ STATIC mp_obj_t machine_soft_spi_make_new(mp_arg_val_t *args) {
     self->base.type = &machine_soft_spi_type;
 
     // set parameters
-    self->baudrate = args[ARG_NEW_baudrate].u_int;
+    self->delay_half = baudrate_to_delay_half(args[ARG_NEW_baudrate].u_int);
     self->polarity = args[ARG_NEW_polarity].u_int;
     self->phase = args[ARG_NEW_phase].u_int;
     if (args[ARG_NEW_bits].u_int != 8) {
@@ -989,7 +1002,7 @@ STATIC void machine_soft_spi_init(mp_obj_t self_in, mp_arg_val_t *args) {
 
     // update parameters
     if (args[ARG_INIT_baudrate].u_int != -1) {
-        self->baudrate = args[ARG_INIT_baudrate].u_int;
+        self->delay_half = baudrate_to_delay_half(args[ARG_INIT_baudrate].u_int);
     }
     if (args[ARG_INIT_polarity].u_int != -1) {
         self->polarity = args[ARG_INIT_polarity].u_int;