zephyr: Enable sys.stdin/out/err.

This change enables `sys.stdin`, `sys.stdout` and `sys.stderr` objects.
They are useful for general IO, and also help with testing zephyr boards.

Signed-off-by: Damien George <damien@micropython.org>

ports/zephyr/CMakeLists.txt

@@ -66,6 +66,7 @@ set(MICROPY_SOURCE_SHARED
     runtime/mpirq.c
     runtime/pyexec.c
     runtime/stdout_helpers.c
+    runtime/sys_stdio_mphal.c
     timeutils/timeutils.c
 )
 list(TRANSFORM MICROPY_SOURCE_SHARED PREPEND ${MICROPY_DIR}/shared/)

ports/zephyr/mpconfigport.h

@@ -96,6 +96,7 @@
 #define MICROPY_PY_ZEPHYR           (1)
 #define MICROPY_PY_ZSENSOR          (1)
 #define MICROPY_PY_SYS_MODULES      (0)
+#define MICROPY_PY_SYS_STDFILES     (1)
 #define MICROPY_LONGINT_IMPL        (MICROPY_LONGINT_IMPL_MPZ)
 #define MICROPY_FLOAT_IMPL (MICROPY_FLOAT_IMPL_FLOAT)
 #define MICROPY_PY_BUILTINS_COMPLEX (0)

ports/zephyr/src/zephyr_getchar.c

@@ -49,6 +49,11 @@ static int console_irq_input_hook(uint8_t ch) {
     return 1;
 }
 
+// Returns true if a char is available for reading.
+int zephyr_getchar_check(void) {
+    return i_get != i_put;
+}
+
 int zephyr_getchar(void) {
     mp_hal_wait_sem(&uart_sem, 0);
     if (k_sem_take(&uart_sem, K_MSEC(0)) == 0) {

ports/zephyr/src/zephyr_getchar.h

@@ -17,4 +17,5 @@
 #include <stdint.h>
 
 void zephyr_getchar_init(void);
+int zephyr_getchar_check(void);
 int zephyr_getchar(void);

ports/zephyr/uart_core.c

@@ -26,6 +26,7 @@
 #include <unistd.h>
 #include "py/mpconfig.h"
 #include "py/runtime.h"
+#include "py/stream.h"
 #include "src/zephyr_getchar.h"
 // Zephyr headers
 #include <zephyr/kernel.h>
@@ -52,6 +53,24 @@ static uint8_t mp_console_txbuf[CONFIG_CONSOLE_PUTCHAR_BUFSIZE];
  * Core UART functions to implement for a port
  */
 
+uintptr_t mp_hal_stdio_poll(uintptr_t poll_flags) {
+    uintptr_t ret = 0;
+    if (poll_flags & MP_STREAM_POLL_RD) {
+        #ifdef CONFIG_CONSOLE_SUBSYS
+        // It's not easy to test if tty is readable, so just unconditionally set it for now.
+        ret |= MP_STREAM_POLL_RD;
+        #else
+        if (zephyr_getchar_check()) {
+            ret |= MP_STREAM_POLL_RD;
+        }
+        #endif
+    }
+    if (poll_flags & MP_STREAM_POLL_WR) {
+        ret |= MP_STREAM_POLL_WR;
+    }
+    return ret;
+}
+
 // Receive single character
 int mp_hal_stdin_rx_chr(void) {
     for (;;) {