arm: Cortex-M0: Adapt core register code to M0

The Cortex-M0(+) and in general processors that support only the ARMv6-M
instruction set have a reduced set of registers and fields compared to
the ARMv7-M compliant processors.
This change goes through all core registers and disables or removes
everything that is not part of the ARMv6-M architecture when compiling
for Cortex-M0.

Jira: ZEP-1497

Change-id: I13e2637bb730e69d02f2a5ee687038dc69ad28a8
Signed-off-by: Vinayak Chettimada <[email protected]>
Signed-off-by: Carles Cufi <[email protected]>
Signed-off-by: Kumar Gala <[email protected]>

Author: carlescufi

arch/arm/core/cortex_m/scb.c

@@ -90,6 +90,7 @@ void sys_arch_reboot(int type)
 	DO_REBOOT();
 }
 
+#if !defined(CONFIG_CPU_CORTEX_M0_M0PLUS)
 /**
  *
  * @brief Set the number of priority groups based on the number of exception
@@ -134,3 +135,4 @@ void _ScbNumPriGroupSet(unsigned int n)
 
 	__scs.scb.aircr.val = reg.val;
 }
+#endif /* !CONFIG_CPU_CORTEX_M0_M0PLUS */

arch/arm/core/fault.c

@@ -372,5 +372,7 @@ void _Fault(const NANO_ESF *esf)
  */
 void _FaultInit(void)
 {
+#if !defined(CONFIG_CPU_CORTEX_M0_M0PLUS)
 	_ScbDivByZeroFaultEnable();
+#endif /* !CONFIG_CPU_CORTEX_M0_M0PLUS */
 }

arch/arm/include/cortex_m/exc.h

@@ -55,8 +55,14 @@ static ALWAYS_INLINE int _IsInIsr(void)
 	/*
 	 * IRQs + PendSV (14) + SVC (11) + SYSTICK (15) are interrupts.
 	 * Vectors 12 and 13 are reserved, we'll never be in there
+	 * On ARMv6-M there is no nested execution bit, so we check exception 3,
+	 * hard fault, to a detect a nested exception.
 	 */
+#if defined(CONFIG_CPU_CORTEX_M0_M0PLUS)
+	return (vector > 10) || (vector == 3);
+#else
 	return (vector > 10) || (vector && _ScbIsNestedExc());
+#endif /* CONFIG_CPU_CORTEX_M0_M0PLUS */
 }
 
 /**

include/arch/arm/cortex_m/scb.h

@@ -207,21 +207,6 @@ static inline int _ScbHiPriVectorPendingGet(void)
 	return reg.bit.vectpending;
 }
 
-/**
- *
- * @brief Find out if the currently executing exception is nested
- *
- * This routine determines if the currently executing exception is nested.
- *
- * @return 1 if nested, 0 otherwise
- */
-
-static inline int _ScbIsNestedExc(void)
-{
-	/* !bit == preempted exceptions */
-	return !__scs.scb.icsr.bit.rettobase;
-}
-
 /**
  *
  * @brief Find out if running in thread mode
@@ -280,76 +265,6 @@ static inline uint32_t _ScbActiveVectorGet(void)
 	return __scs.scb.icsr.bit.vectactive;
 }
 
-/**
- *
- * @brief Find out if vector table is in SRAM or ROM
- *
- * This routine determines if the currently executing exception is nested.
- *
- * @return 1 if in SRAM, 0 if in ROM
- */
-
-static inline uint32_t _ScbIsVtableInSram(void)
-{
-	return !!__scs.scb.vtor.bit.tblbase;
-}
-
-/**
- *
- * @brief Move vector table from SRAM to ROM and vice-versa
- *
- * This routine moves the vector table to the given memory region.
- *
- * @return 1 if in SRAM, 0 if in ROM
- */
-
-static inline void _ScbVtableLocationSet(
-	int sram /* 1 to move vector to SRAM, 0 to move it to ROM */
-	)
-{
-	__ASSERT(!(sram & 0xfffffffe), "");
-	__scs.scb.vtor.bit.tblbase = sram;
-}
-
-/**
- *
- * @brief Obtain base address of vector table
- *
- * This routine returns the vector table's base address.
- *
- * @return the base address of the vector table
- */
-
-static inline uint32_t _ScbVtableAddrGet(void)
-{
-	return __scs.scb.vtor.bit.tbloff;
-}
-
-/**
- *
- * @brief Set base address of vector table
- *
- * @a addr must align to the number of exception entries in vector table:
- *
- *    numException = 16 + num_interrupts where each entry is 4 Bytes
- *
- * As a minimum, @a addr must be a multiple of 128:
- *
- *  0 <= num_interrupts <  16: multiple 0x080
- * 16 <= num_interrupts <  48: multiple 0x100
- * 48 <= num_interrupts < 112: multiple 0x200
- *               ....
- * @param addr base address, aligned on 128 minimum
- *
- * @return N/A
- */
-
-static inline void _ScbVtableAddrSet(uint32_t addr)
-{
-	__ASSERT(!(addr & 0x7F), "invalid vtable base Addr");
-	__scs.scb.vtor.bit.tbloff = addr;
-}
-
 /**
  *
  * @brief Find out if data regions are little endian
@@ -365,22 +280,6 @@ static inline int _ScbIsDataLittleEndian(void)
 	return !(__scs.scb.aircr.bit.endianness);
 }
 
-/**
- *
- * @brief Get the programmed number of priority groups
- *
- * Exception priorities can be sub-divided into groups, with sub-priorities.
- * Within these groups, exceptions do not preempt each other. The sub-priorities
- * are only used to decide which exception will run when several are pending.
- *
- * @return the number of priority groups
- */
-
-static inline int _ScbNumPriGroupGet(void)
-{
-	return 1 << (7 - __scs.scb.aircr.bit.prigroup);
-}
-
 /**
  *
  * @brief CPU goes to sleep after exiting an ISR
@@ -478,36 +377,6 @@ static inline void _ScbSleepDeepClear(void)
 	__scs.scb.scr.bit.sleepdeep = 0;
 }
 
-/**
- *
- * @brief Enable faulting on division by zero
- *
- * This routine enables the divide by zero fault.
- * By default, the CPU ignores the error.
- *
- * @return N/A
- */
-
-static inline void _ScbDivByZeroFaultEnable(void)
-{
-	__scs.scb.ccr.bit.div_0_trp = 1;
-}
-
-/**
- *
- * @brief Ignore division by zero errors
- *
- * This routine disables the divide by zero fault.
- * This is the default behavior.
- *
- * @return N/A
- */
-
-static inline void _ScbDivByZeroFaultDisable(void)
-{
-	__scs.scb.ccr.bit.div_0_trp = 0;
-}
-
 /**
  *
  * @brief Enable faulting on unaligned access
@@ -614,6 +483,136 @@ static inline void _ScbExcPrioSet(uint8_t exc, uint8_t pri)
 }
 
 #if !defined(CONFIG_CPU_CORTEX_M0_M0PLUS)
+/**
+ *
+ * @brief Find out if the currently executing exception is nested
+ *
+ * This routine determines if the currently executing exception is nested.
+ *
+ * @return 1 if nested, 0 otherwise
+ */
+
+static inline int _ScbIsNestedExc(void)
+{
+	/* !bit == preempted exceptions */
+	return !__scs.scb.icsr.bit.rettobase;
+}
+
+/**
+ *
+ * @brief Find out if vector table is in SRAM or ROM
+ *
+ * This routine determines if the currently executing exception is nested.
+ *
+ * @return 1 if in SRAM, 0 if in ROM
+ */
+
+static inline uint32_t _ScbIsVtableInSram(void)
+{
+	return !!__scs.scb.vtor.bit.tblbase;
+}
+
+/**
+ *
+ * @brief Move vector table from SRAM to ROM and vice-versa
+ *
+ * This routine moves the vector table to the given memory region.
+ *
+ * @return 1 if in SRAM, 0 if in ROM
+ */
+
+static inline void _ScbVtableLocationSet(
+	int sram /* 1 to move vector to SRAM, 0 to move it to ROM */
+	)
+{
+	__ASSERT(!(sram & 0xfffffffe), "");
+	__scs.scb.vtor.bit.tblbase = sram;
+}
+
+/**
+ *
+ * @brief Obtain base address of vector table
+ *
+ * This routine returns the vector table's base address.
+ *
+ * @return the base address of the vector table
+ */
+
+static inline uint32_t _ScbVtableAddrGet(void)
+{
+	return __scs.scb.vtor.bit.tbloff;
+}
+
+/**
+ *
+ * @brief Set base address of vector table
+ *
+ * @a addr must align to the number of exception entries in vector table:
+ *
+ *    numException = 16 + num_interrupts where each entry is 4 Bytes
+ *
+ * As a minimum, @a addr must be a multiple of 128:
+ *
+ *  0 <= num_interrupts <  16: multiple 0x080
+ * 16 <= num_interrupts <  48: multiple 0x100
+ * 48 <= num_interrupts < 112: multiple 0x200
+ *               ....
+ * @param addr base address, aligned on 128 minimum
+ *
+ * @return N/A
+ */
+
+static inline void _ScbVtableAddrSet(uint32_t addr)
+{
+	__ASSERT(!(addr & 0x7F), "invalid vtable base Addr");
+	__scs.scb.vtor.bit.tbloff = addr;
+}
+
+/**
+ *
+ * @brief Enable faulting on division by zero
+ *
+ * This routine enables the divide by zero fault.
+ * By default, the CPU ignores the error.
+ *
+ * @return N/A
+ */
+
+static inline void _ScbDivByZeroFaultEnable(void)
+{
+	__scs.scb.ccr.bit.div_0_trp = 1;
+}
+
+/**
+ *
+ * @brief Ignore division by zero errors
+ *
+ * This routine disables the divide by zero fault.
+ * This is the default behavior.
+ *
+ * @return N/A
+ */
+
+static inline void _ScbDivByZeroFaultDisable(void)
+{
+	__scs.scb.ccr.bit.div_0_trp = 0;
+}
+
+/**
+ *
+ * @brief Get the programmed number of priority groups
+ *
+ * Exception priorities can be sub-divided into groups, with sub-priorities.
+ * Within these groups, exceptions do not preempt each other. The sub-priorities
+ * are only used to decide which exception will run when several are pending.
+ *
+ * @return the number of priority groups
+ */
+
+static inline int _ScbNumPriGroupGet(void)
+{
+	return 1 << (7 - __scs.scb.aircr.bit.prigroup);
+}
 
 /**
  *