From dd5e47a4184ff6f586eff0dd3a495359302fb79d Mon Sep 17 00:00:00 2001
From: Angus Gratton <angus@espressif.com>
Date: Wed, 14 Dec 2016 08:15:03 -0600
Subject: [PATCH] ESP32 core v2: Two changes (1) flushes the UART TX buffer in
 the esp32 serial shutdown routine. The ROM bootloader does not flush the FIFO
 before handing over to user code, so some of this output is not currently
 seen when the UART is reconfigured in early stages of startup.  And changes
 the openocd config file's default flash voltage from 1.8V to 3.3V. This is
 not necessary right now, but may save some hard-to-debug moments down the
 track (3.3V-only flash running at 1.8V often half-works and does weird
 things...)

---
 arch/xtensa/src/esp32/esp32_serial.c     | 13 +++++++++++++
 configs/esp32-core/scripts/esp32.cfg     |  6 ++----
 configs/esp32-core/scripts/esp32_iram.ld |  4 ----
 3 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/arch/xtensa/src/esp32/esp32_serial.c b/arch/xtensa/src/esp32/esp32_serial.c
index f48b06e304f..34846e89e8f 100644
--- a/arch/xtensa/src/esp32/esp32_serial.c
+++ b/arch/xtensa/src/esp32/esp32_serial.c
@@ -586,6 +586,19 @@ static int esp32_setup(struct uart_dev_s *dev)
 static void esp32_shutdown(struct uart_dev_s *dev)
 {
   struct esp32_dev_s *priv = (struct esp32_dev_s *)dev->priv;
+  uint32_t status;
+
+  /* Wait for outgoing FIFO to clear.   The ROM bootloader does not flush
+   * the FIFO before handing over to user code, so some of this output is
+   * not currently seen when the UART is reconfigured in early stages of
+   * startup.
+   */
+
+  do
+    {
+      status = esp32_serialin(priv, UART_STATUS_OFFSET);
+    }
+  while ((status & UART_TXFIFO_CNT_M) != 0);
 
   /* Disable all UART interrupts */
 
diff --git a/configs/esp32-core/scripts/esp32.cfg b/configs/esp32-core/scripts/esp32.cfg
index 0bd581f40a0..a9f94d37dc8 100644
--- a/configs/esp32-core/scripts/esp32.cfg
+++ b/configs/esp32-core/scripts/esp32.cfg
@@ -44,8 +44,6 @@ source [find target/esp32.cfg]
 # voltage greatly.
 
 # Enable this for 1.8V SPI flash
-esp108 flashbootstrap 1.8
+# esp108 flashbootstrap 1.8
 # Enable this for 3.3V SPI flash
-#esp108 flashbootstrap 3.3
-
-
+esp108 flashbootstrap 3.3
diff --git a/configs/esp32-core/scripts/esp32_iram.ld b/configs/esp32-core/scripts/esp32_iram.ld
index 605ea54e5a3..62ed31380bc 100644
--- a/configs/esp32-core/scripts/esp32_iram.ld
+++ b/configs/esp32-core/scripts/esp32_iram.ld
@@ -173,10 +173,6 @@ SECTIONS
     _sheap = ABSOLUTE(.);
   } >dram0_0_seg
 
-  .flash.rodata :
-  {
-  } >drom0_0_seg
-
   .rtc.text :
   {
     . = ALIGN(4);