Add an alternate STM32 I2C driver that works around errata in the F103 chip (and maybe others). From Patrizio Simona

arch/arm/include/sam34/chip.h

@@ -831,10 +831,10 @@
  * bits[7:4] of each field, bits[3:0] read as zero and ignore writes.
  */
 
-#define NVIC_SYSH_PRIORITY_MIN       0xf0 /* All bits[7:4] set is minimum priority */
-#define NVIC_SYSH_PRIORITY_DEFAULT   0x80 /* Midpoint is the default */
-#define NVIC_SYSH_PRIORITY_MAX       0x00 /* Zero is maximum priority */
-#define NVIC_SYSH_PRIORITY_STEP      0x10 /* Four bits of interrupt priority used */
+#define NVIC_SYSH_PRIORITY_MIN        0xf0 /* All bits[7:4] set is minimum priority */
+#define NVIC_SYSH_PRIORITY_DEFAULT    0x80 /* Midpoint is the default */
+#define NVIC_SYSH_PRIORITY_MAX        0x00 /* Zero is maximum priority */
+#define NVIC_SYSH_PRIORITY_STEP       0x10 /* Four bits of interrupt priority used */
 
 /* If CONFIG_ARMV7M_USEBASEPRI is selected, then interrupts will be disabled
  * by setting the BASEPRI register to NVIC_SYSH_DISABLE_PRIORITY so that most

arch/arm/src/stm32/Kconfig

@@ -3052,6 +3052,17 @@ endmenu
 menu "I2C Configuration"
 	depends on STM32_I2C
 
+config STM32_I2C_ALT
+	bool "Alternate I2C implementation"
+	default n if !STM32_PERFORMANCELINE
+	default y if STM32_PERFORMANCELINE
+	---help---
+		This selection enables an alternative I2C driver.  This alternate
+		driver implements some rather complex workarounds for errata against
+		the STM32 F103 "Performance Line".  This selection is an option
+		because: (1) It has not yet been fully verified and (2) It is not
+		certain that he scope of this workaround is needed only for the F103.
+
 config STM32_I2C_DYNTIMEO
 	bool "Use dynamic timeouts"
 	default n

arch/arm/src/stm32/Make.defs

@@ -105,11 +105,15 @@ ifeq ($(CONFIG_NUTTX_KERNEL),y)
 CHIP_CSRCS += stm32_userspace.c stm32_mpuinit.c
 endif
 
+ifeq ($(CONFIG_STM32_I2C_ALT),y)
+CHIP_CSRCS += stm32_i2c_alt.c
+else
 ifeq ($(CONFIG_STM32_STM32F30XX),y)
 CHIP_CSRCS += stm32f30xxx_i2c.c
 else
 CHIP_CSRCS += stm32_i2c.c
 endif
+endif
 
 ifeq ($(CONFIG_USBDEV),y)
 ifeq ($(CONFIG_STM32_USB),y)