From 24816cb08b0742ca055ebeb9a362148c9230d011 Mon Sep 17 00:00:00 2001
From: Gregory Nutt <gnutt@nuttx.org>
Date: Fri, 10 Mar 2017 10:25:11 -0600
Subject: [PATCH] All STM32 host drivers.  In IN endpoint retry, delay for a
 clock tick to give some breathing space for the CPU.  EXPERIMENTAL change.

---
 arch/arm/src/stm32/stm32_otgfshost.c     | 8 ++++++++
 arch/arm/src/stm32/stm32_otghshost.c     | 8 ++++++++
 arch/arm/src/stm32f7/stm32_otghost.c     | 8 ++++++++
 arch/arm/src/stm32l4/stm32l4_otgfshost.c | 8 ++++++++
 4 files changed, 32 insertions(+)

diff --git a/arch/arm/src/stm32/stm32_otgfshost.c b/arch/arm/src/stm32/stm32_otgfshost.c
index 2c6bda6773..7451289b27 100644
--- a/arch/arm/src/stm32/stm32_otgfshost.c
+++ b/arch/arm/src/stm32/stm32_otgfshost.c
@@ -1906,6 +1906,14 @@ static ssize_t stm32_in_transfer(FAR struct stm32_usbhost_s *priv, int chidx,
 
                       return (ssize_t)ret;
                     }
+
+                  /* Wait a bit before retrying after a NAK.
+                   *
+                   * REVISIT:  This is intended to give the CPU a break from
+                   * the tight polling loop.  But are there performance issues?
+                   */
+
+                  usleep(1000);
                 }
             }
           else
diff --git a/arch/arm/src/stm32/stm32_otghshost.c b/arch/arm/src/stm32/stm32_otghshost.c
index 71f46ff4a3..85092d89a9 100644
--- a/arch/arm/src/stm32/stm32_otghshost.c
+++ b/arch/arm/src/stm32/stm32_otghshost.c
@@ -1911,6 +1911,14 @@ static ssize_t stm32_in_transfer(FAR struct stm32_usbhost_s *priv, int chidx,
 
                       return (ssize_t)ret;
                     }
+
+                  /* Wait a bit before retrying after a NAK.
+                   *
+                   * REVISIT:  This is intended to give the CPU a break from
+                   * the tight polling loop.  But are there performance issues?
+                   */
+
+                  usleep(1000);
                 }
             }
           else
diff --git a/arch/arm/src/stm32f7/stm32_otghost.c b/arch/arm/src/stm32f7/stm32_otghost.c
index 48e4418539..a89be679b9 100644
--- a/arch/arm/src/stm32f7/stm32_otghost.c
+++ b/arch/arm/src/stm32f7/stm32_otghost.c
@@ -1905,6 +1905,14 @@ static ssize_t stm32_in_transfer(FAR struct stm32_usbhost_s *priv, int chidx,
 
                       return (ssize_t)ret;
                     }
+
+                  /* Wait a bit before retrying after a NAK.
+                   *
+                   * REVISIT:  This is intended to give the CPU a break from
+                   * the tight polling loop.  But are there performance issues?
+                   */
+
+                  usleep(1000);
                 }
             }
           else
diff --git a/arch/arm/src/stm32l4/stm32l4_otgfshost.c b/arch/arm/src/stm32l4/stm32l4_otgfshost.c
index 33f283e167..a488825b9c 100644
--- a/arch/arm/src/stm32l4/stm32l4_otgfshost.c
+++ b/arch/arm/src/stm32l4/stm32l4_otgfshost.c
@@ -1910,6 +1910,14 @@ static ssize_t stm32l4_in_transfer(FAR struct stm32l4_usbhost_s *priv,
 
                       return (ssize_t)ret;
                     }
+
+                  /* Wait a bit before retrying after a NAK.
+                   *
+                   * REVISIT:  This is intended to give the CPU a break from
+                   * the tight polling loop.  But are there performance issues?
+                   */
+
+                  usleep(1000);
                 }
             }
           else