Merge pull request #7673 from gamblor21/atmel-spi-tx-len-fix

Fix for long length SPI writes on ATMEL

Author: jepler

ports/atmel-samd/common-hal/busio/SPI.c

@@ -268,7 +268,14 @@ bool common_hal_busio_spi_write(busio_spi_obj_t *self,
     }
     int32_t status;
     if (len >= 16) {
-        status = sercom_dma_write(self->spi_desc.dev.prvt, data, len);
+        size_t bytes_remaining = len;
+
+        // Maximum DMA transfer is 65535
+        while (bytes_remaining > 0) {
+            size_t to_send = (bytes_remaining > 65535) ? 65535 : bytes_remaining;
+            status = sercom_dma_write(self->spi_desc.dev.prvt, data + (len - bytes_remaining), to_send);
+            bytes_remaining -= to_send;
+        }
     } else {
         struct io_descriptor *spi_io;
         spi_m_sync_get_io_descriptor(&self->spi_desc, &spi_io);