nrf/modules/machine/uart: Support sending data stored in flash.

Signed-off-by: Andrew Leech <andrew@alelec.net>

ports/nrf/modules/machine/uart.c

@@ -29,6 +29,7 @@
 // This file is never compiled standalone, it's included directly from
 // extmod/machine_uart.c via MICROPY_PY_MACHINE_UART_INCLUDEFILE.
 
+#include <string.h>
 #include "py/mperrno.h"
 #include "py/mphal.h"
 #include "py/ringbuf.h"
@@ -317,10 +318,30 @@ static mp_uint_t mp_machine_uart_read(mp_obj_t self_in, void *buf_in, mp_uint_t
     return size;
 }
 
-static mp_uint_t mp_machine_uart_write(mp_obj_t self_in, const void *buf_in, mp_uint_t size, int *errcode) {
-    machine_uart_obj_t *self = self_in;
+static mp_uint_t mp_machine_uart_write(mp_obj_t self_in, const void *buf, mp_uint_t size, int *errcode) {
+    #if !NRFX_UART_ENABLED
+    if (!nrfx_is_in_ram(buf)) {
+        // Peripherals using EasyDMA require that transfer buffers are placed in DataRAM,
+        // they cannot access data directly from flash.
+        // If buf is in flash, copy to ram in chunks to send.
+        char rambuf[64];
+        char *flashbuf = (char *)buf;
+        mp_uint_t remaining = size;
+        while (remaining) {
+            mp_uint_t chunk = MIN(sizeof(rambuf), remaining);
+            memcpy(rambuf, flashbuf, chunk);
+            if (mp_machine_uart_write(self_in, rambuf, chunk, errcode) == MP_STREAM_ERROR) {
+                return MP_STREAM_ERROR;
+            }
+            remaining -= chunk;
+            flashbuf += chunk;
+        }
+        return size;
+    }
+    #endif
 
-    nrfx_err_t err = nrfx_uart_tx(self->p_uart, buf_in, size);
+    machine_uart_obj_t *self = self_in;
+    nrfx_err_t err = nrfx_uart_tx(self->p_uart, buf, size);
     if (err == NRFX_SUCCESS) {
         while (nrfx_uart_tx_in_progress(self->p_uart)) {
             MICROPY_EVENT_POLL_HOOK;