diff --git a/arch/arm/src/a1x/a1x_boot.c b/arch/arm/src/a1x/a1x_boot.c
index 203de866f8..8b0cf23c1a 100644
--- a/arch/arm/src/a1x/a1x_boot.c
+++ b/arch/arm/src/a1x/a1x_boot.c
@@ -139,6 +139,8 @@ static inline void a1x_setupmappings(void)
 {
   int i;
 
+  /* Set up each group of section mappings */
+
   for (i = 0; i < NMAPPINGS; i++)
     {
       mmu_l1_map_region(&section_mapping[i]);
@@ -162,7 +164,7 @@ static void a1x_vectorpermissions(uint32_t mmuflags)
 
   uint32_t pte = mmu_l2_getentry(PG_L2_VECT_VADDR, 0);
 
-  /* String the MMU flags from the page table entry.
+  /* Mask out the old MMU flags from the page table entry.
    *
    * The pte might be zero the first time this function is called.
    */
diff --git a/arch/arm/src/armv7-a/arm_head.S b/arch/arm/src/armv7-a/arm_head.S
index a049f1c017..25ccb38bcc 100644
--- a/arch/arm/src/armv7-a/arm_head.S
+++ b/arch/arm/src/armv7-a/arm_head.S
@@ -225,7 +225,7 @@ __start:
 	 * mapped RAM in either case.  So we will need to create a special
 	 * mapping for the page table.
 	 *
-	 * Load informtion needed to map the page table.  After the ldmia, we
+	 * Load information needed to map the page table.  After the ldmia, we
 	 * will have
 	 *
 	 *   R1 = The aligned, physical base address of the page table
diff --git a/arch/arm/src/armv7-a/arm_mmu.c b/arch/arm/src/armv7-a/arm_mmu.c
index ee310c25e3..f82490caf8 100644
--- a/arch/arm/src/armv7-a/arm_mmu.c
+++ b/arch/arm/src/armv7-a/arm_mmu.c
@@ -165,7 +165,7 @@ void mmu_l1_map_region(const struct section_mapping_s *mapping)
   uint32_t mmuflags = mapping->mmuflags;
   int i;
 
-  /* Loop, writting each mapping into the L1 page table */
+  /* Loop, writing each mapping into the L1 page table */
 
   for (i = 0; i < mapping->nsections; i++)
     {
@@ -194,7 +194,7 @@ void mmu_invalidate_region(uint32_t vstart, size_t size)
   uint32_t vaddr = vstart & 0xfffff000;
   uint32_t vend  = vaddr + size;
 
-  /* Loop, writting each mapping into the L1 page table */
+  /* Loop, writing each mapping into the L1 page table */
 
   while (vaddr < vend)
     {
diff --git a/arch/arm/src/sama5/sam_boot.c b/arch/arm/src/sama5/sam_boot.c
index 2351e26daa..a2a7fc8628 100644
--- a/arch/arm/src/sama5/sam_boot.c
+++ b/arch/arm/src/sama5/sam_boot.c
@@ -321,6 +321,8 @@ static inline void sam_setupmappings(void)
 {
   int i;
 
+  /* Set up each group of section mappings */
+
   for (i = 0; i < NMAPPINGS; i++)
     {
       mmu_l1_map_region(&section_mapping[i]);
@@ -341,6 +343,8 @@ static inline void sam_remap(void)
 {
   int i;
 
+  /* Re-map each group of section */
+
   for (i = 0; i < NREMAPPINGS; i++)
     {
       mmu_l1_map_region(&operational_mapping[i]);
@@ -364,7 +368,7 @@ static void sam_vectorpermissions(uint32_t mmuflags)
 
   uint32_t pte = mmu_l2_getentry(PG_L2_VECT_VADDR, 0);
 
-  /* String the MMU flags from the page table entry.
+  /* Mask out the old MMU flags from the page table entry.
    *
    * The pte might be zero the first time this function is called.
    */
diff --git a/configs/pcduino-a10/README.txt b/configs/pcduino-a10/README.txt
index 2e40c04a9a..3d193a51f0 100644
--- a/configs/pcduino-a10/README.txt
+++ b/configs/pcduino-a10/README.txt
@@ -255,10 +255,28 @@ Booting NuttX from an SD card
 
   These are the steps to get U-Boot booting from SD Card:
 
-    $ git clone https://github.com/yuq/u-boot-sunxi.git
-    $ cd u-boot-sunxi
-    $ make pcduino CROSS_COMPILE=arm-none-eabi-
-    $ sudo dd if=./spl/sunxi-spl.bin of=/dev/sdb bs=1024 seek=8
-    $ sudo dd if=nuttx.bin of=/dev/sdb bs=1024 seek=32
+    1. Get the U-Boot sources for the pcDuino
+
+      $ git clone https://github.com/yuq/u-boot-sunxi.git
+
+    2. Build U-Boot.  We really only want the SPL program; this builds
+       the whole thing:
+
+      $ cd u-boot-sunxi
+      $ make pcduino CROSS_COMPILE=arm-none-eabi-
+
+      NOTES:
+      a. You may need to use a different tool prefix for the CROSS_COMPILE=
+         value, depending upon what toolchain you have installed and upon
+         which platform your are working.
+      b. When I try this on Cygwin, I get a make failure that is, apparently,
+         due to some script incompatibility.
+
+    3. Insert a FLASH stick.  Use dmesg to get the name of the new USB
+       device.  Make sure that it is not mounted, then (assuming that the
+       USB device is /dev/sdb):
+
+      $ sudo dd if=./spl/sunxi-spl.bin of=/dev/sdb bs=1024 seek=8
+      $ sudo dd if=nuttx.bin of=/dev/sdb bs=1024 seek=32
 
   Reference: https://www.olimex.com/wiki/Bare_Metal_programming_A13#Stand_alone_program_running_with_uboot