Explicate .pio file usage

Author: dhalbert

ports/raspberrypi/common-hal/audiobusio/I2SOut.c

@@ -19,7 +19,9 @@
 #include "bindings/rp2pio/StateMachine.h"
 
 const uint16_t i2s_program[] = {
-/*
+
+/* From i2s.pio:
+
 .program i2s
 .side_set 2
 
@@ -55,7 +57,8 @@ const uint16_t i2s_program[] = {
 
 
 const uint16_t i2s_program_left_justified[] = {
-/*
+/* From i2s_left.pio:
+
 .program i2s
 .side_set 2
 
@@ -91,7 +94,8 @@ const uint16_t i2s_program_left_justified[] = {
 
 // Another version of i2s_program with the LRCLC and BCLK pin swapped
 const uint16_t i2s_program_swap[] = {
-/*
+/* From i2s_swap.pio:
+
 .program i2s
 .side_set 2
 
@@ -128,7 +132,8 @@ const uint16_t i2s_program_swap[] = {
 // Another version of i2s_program_left_justified with the LRCLC and BCLK pin
 // swapped.
 const uint16_t i2s_program_left_justified_swap[] = {
-/*
+/* From i2s_swap_left.pio:
+
 .program i2s
 .side_set 2
 

ports/raspberrypi/common-hal/audiobusio/README.pio

@@ -1 +1,7 @@
 .pio files right now are compiled by hand with pico-sdk/tools/pioasm and inserted into I2SOut.c
+
+i2s.pio           regular pin order, not left_justified
+i2s_left.pio      regular pin order, left_justified
+
+i2s_swap.pio      swapped pin order, not left_justified
+i2s_swap_left.pio swapped pin order, left_justified