armcm_boot: Add generic code for early board init on armcm machines

Add basic ARM Cortex-M C init code and build linker scripts to
src/generic/ code.  This can be used to simplify the various ARM board
code.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

5 files changed, 202 insertions, 0 deletions

diff --git a/scripts/buildcommands.py b/scripts/buildcommands.py
index e796994e..6ef5c80a 100644
--- a/scripts/buildcommands.py
+++ b/scripts/buildcommands.py
@@ -210,6 +210,50 @@ Handlers.append(HandleInitialPins())
 
 
 ######################################################################
+# ARM IRQ vector table generation
+######################################################################
+
+# Create ARM IRQ vector table from interrupt handler declarations
+class Handle_arm_irq:
+    def __init__(self):
+        self.irqs = {}
+        self.ctr_dispatch = { 'DECL_ARMCM_IRQ': self.decl_armcm_irq }
+    def decl_armcm_irq(self, req):
+        func, num = req.split()[1:]
+        num = decode_integer(num)
+        if num in self.irqs and self.irqs[num] != func:
+            error("Conflicting IRQ definition %d (old %s new %s)"
+                  % (num, self.irqs[num], func))
+        self.irqs[num] = func
+    def update_data_dictionary(self, data):
+        pass
+    def generate_code(self, options):
+        armcm_offset = 16
+        if 1 - armcm_offset not in self.irqs:
+            # The ResetHandler was not defined - don't build VectorTable
+            return ""
+        max_irq = max(self.irqs.keys())
+        table = ["    DefaultHandler,\n"] * (max_irq + armcm_offset + 1)
+        defs = []
+        for num, func in self.irqs.items():
+            if num < 1 - armcm_offset:
+                error("Invalid IRQ %d (%s)" % (num, func))
+            defs.append("extern void %s(void);\n" % (func,))
+            table[num + armcm_offset] = "    %s,\n" % (func,)
+        table[0] = "    &_stack_end,\n"
+        fmt = """
+extern void DefaultHandler(void);
+extern uint32_t _stack_end;
+%s
+const void *VectorTable[] __visible __section(".vector_table") = {
+%s};
+"""
+        return fmt % (''.join(defs), ''.join(table))
+
+Handlers.append(Handle_arm_irq())
+
+
+######################################################################
 # Wire protocol commands and responses
 ######################################################################
 
diff --git a/src/generic/armcm_boot.c b/src/generic/armcm_boot.c
new file mode 100644
index 00000000..c559c1c1
--- /dev/null
+++ b/src/generic/armcm_boot.c
@@ -0,0 +1,73 @@
+// ARM Cortex-M vector table and initial bootup handling
+//
+// Copyright (C) 2019  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include "armcm_boot.h" // DECL_ARMCM_IRQ
+#include "board/internal.h" // SystemInit
+
+// Symbols created by armcm_boot.lds.S linker script
+extern uint32_t _data_start, _data_end, _data_flash;
+extern uint32_t _bss_start, _bss_end, _stack_start;
+
+
+/****************************************************************
+ * Basic interrupt handlers
+ ****************************************************************/
+
+// Initial code entry point - invoked by the processor after a reset
+void
+ResetHandler(void)
+{
+    // Copy global variables from flash to ram
+    uint32_t count = (&_data_end - &_data_start) * 4;
+    __builtin_memcpy(&_data_start, &_data_flash, count);
+
+    // Clear the bss segment
+    __builtin_memset(&_bss_start, 0, (&_bss_end - &_bss_start) * 4);
+
+    barrier();
+
+    // Initializing the C library isn't needed...
+    //__libc_init_array();
+
+    // Initialize the machine
+    SystemInit();
+
+    // Run the main code
+    extern int main(void);
+    main();
+
+    // The main() call should not return
+    for (;;)
+        ;
+}
+DECL_ARMCM_IRQ(ResetHandler, -15);
+
+// Code called for any undefined interrupts
+void
+DefaultHandler(void)
+{
+    for (;;)
+        ;
+}
+
+
+/****************************************************************
+ * Dynamic memory range
+ ****************************************************************/
+
+// Return the start of memory available for dynamic allocations
+void *
+dynmem_start(void)
+{
+    return &_bss_end;
+}
+
+// Return the end of memory available for dynamic allocations
+void *
+dynmem_end(void)
+{
+    return &_stack_start;
+}
diff --git a/src/generic/armcm_boot.h b/src/generic/armcm_boot.h
new file mode 100644
index 00000000..10b17e18
--- /dev/null
+++ b/src/generic/armcm_boot.h
@@ -0,0 +1,20 @@
+#ifndef __GENERIC_ARMCM_BOOT_H
+#define __GENERIC_ARMCM_BOOT_H
+
+#include "ctr.h" // DECL_CTR_INT
+
+// Declare an IRQ handler
+#define DECL_ARMCM_IRQ(FUNC, NUM)                               \
+    DECL_CTR_INT("DECL_ARMCM_IRQ " __stringify(FUNC), (NUM))
+
+// Statically declare an IRQ handler and run-time enable it
+#define armcm_enable_irq(FUNC, NUM, PRIORITY) do {      \
+        DECL_ARMCM_IRQ(FUNC, (NUM));                    \
+        NVIC_SetPriority((NUM), (PRIORITY));            \
+        NVIC_EnableIRQ((NUM));                          \
+    } while (0)
+
+// Vectors created by scripts/buildcommands.py from DECL_ARMCM_IRQ commands
+extern const void * const VectorTable[];
+
+#endif // armcm_boot.h
diff --git a/src/generic/armcm_boot.lds.S b/src/generic/armcm_boot.lds.S
new file mode 100644
index 00000000..8014a490
--- /dev/null
+++ b/src/generic/armcm_boot.lds.S
@@ -0,0 +1,63 @@
+// Generic ARM Cortex-M linker script
+//
+// Copyright (C) 2019  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include "autoconf.h" // CONFIG_FLASH_START
+
+OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
+OUTPUT_ARCH(arm)
+
+MEMORY
+{
+  rom (rx) : ORIGIN = CONFIG_FLASH_START , LENGTH = CONFIG_FLASH_SIZE
+  ram (rwx) : ORIGIN = CONFIG_RAM_START , LENGTH = CONFIG_RAM_SIZE
+}
+
+SECTIONS
+{
+    .text : {
+        . = ALIGN(4);
+        KEEP(*(.vector_table))
+        *(.text .text.*)
+        *(.rodata .rodata*)
+    } > rom
+
+    . = ALIGN(4);
+    _data_flash = .;
+
+    .data : AT (_data_flash)
+    {
+        . = ALIGN(4);
+        _data_start = .;
+        *(.ramfunc .ramfunc.*);
+        *(.data .data.*);
+        . = ALIGN(4);
+        _data_end = .;
+    } > ram
+
+    .bss (NOLOAD) :
+    {
+        . = ALIGN(4);
+        _bss_start = .;
+        *(.bss .bss.*)
+        *(COMMON)
+        . = ALIGN(4);
+        _bss_end = .;
+    } > ram
+
+    _stack_start = CONFIG_RAM_START + CONFIG_RAM_SIZE - CONFIG_STACK_SIZE ;
+    .stack _stack_start (NOLOAD) :
+    {
+        . = . + CONFIG_STACK_SIZE;
+        _stack_end = .;
+    } > ram
+
+    /DISCARD/ : {
+        // The .init/.fini sections are used by __libc_init_array(), but
+        // that isn't needed so no need to include them in the binary.
+        *(.init)
+        *(.fini)
+    }
+}
diff --git a/src/generic/armcm_timer.c b/src/generic/armcm_timer.c
index f4ce2b8b..ef38680a 100644
--- a/src/generic/armcm_timer.c
+++ b/src/generic/armcm_timer.c
@@ -5,6 +5,7 @@
 // This file may be distributed under the terms of the GNU GPLv3 license.
 
 #include "autoconf.h" // CONFIG_CLOCK_FREQ
+#include "armcm_boot.h" // DECL_ARMCM_IRQ
 #include "board/internal.h" // SysTick
 #include "board/irq.h" // irq_disable
 #include "board/misc.h" // timer_from_us
@@ -160,6 +161,7 @@ SysTick_Handler(void)
     timer_set_diff(diff);
     irq_enable();
 }
+DECL_ARMCM_IRQ(SysTick_Handler, SysTick_IRQn);
 
 // Make sure timer_repeat_until doesn't wrap 32bit comparisons
 void