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circuitpython/ports/rp2/memmap_mp.ld
cpottle9 c80e7c14e6 rp2: Allocate GC heap from unused RAM. 
Borrowing an idea from the mimxrt port (also stm32 port): in the loader
input file memmap_mp.ld calculate __GcHeapStart and __GcHeapEnd as the
unused RAM.  Then in main.c use these addresses as arguments to gc_init().

The benefits of this change are:

1) When libraries are added or removed in the future changing BSS usage,
   main.c's sizing of the GC heap does not need to be changed.

2) Currently these changes make the GC area about 30 KBytes larger, eg on
   PICO_W the GC heap increases from 166016 to 192448 bytes.  Without that
   change this RAM would never get used.

3) If someone wants to disable one or more SRAM blocks on the RP2040 to
   reduce power consumption it will be easy: just change the MEMORY section
   in memmap_mp.ld.  For instance to not use SRAM2 and SRAM3 change it to:

        MEMORY
        {
            FLASH(rx) : ORIGIN = 0x10000000, LENGTH = 2048k
            RAM(rwx) : ORIGIN =  0x21000000, LENGTH = 128k
            SCRATCH_X(rwx) : ORIGIN = 0x20040000, LENGTH = 4k
            SCRATCH_Y(rwx) : ORIGIN = 0x20041000, LENGTH = 4k
        }

   Then to turn off clocks for SRAM2 and SRAM3 from MicroPython, set the
   appropriate bits in WAKE_EN0 and SLEEP_EN0.

Tested by running the firmware.uf2 file on PICO_W and displaying
micropython.mem_info().  Confirmed GC total size approximately matched the
size calculated by the loader.

Signed-off-by: cpottle9 <cpottle9@outlook.com>
2023-03-09 12:00:02 +11:00

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/* Based on GCC ARM embedded samples.
Defines the following symbols for use by code:
__exidx_start
__exidx_end
__etext
__data_start__
__preinit_array_start
__preinit_array_end
__init_array_start
__init_array_end
__fini_array_start
__fini_array_end
__data_end__
__bss_start__
__bss_end__
__end__
end
__HeapLimit
__StackLimit
__StackTop
__stack (== StackTop)
*/
MEMORY
{
FLASH(rx) : ORIGIN = 0x10000000, LENGTH = 2048k
RAM(rwx) : ORIGIN = 0x20000000, LENGTH = 256k
SCRATCH_X(rwx) : ORIGIN = 0x20040000, LENGTH = 4k
SCRATCH_Y(rwx) : ORIGIN = 0x20041000, LENGTH = 4k
}
ENTRY(_entry_point)
SECTIONS
{
/* Second stage bootloader is prepended to the image. It must be 256 bytes big
and checksummed. It is usually built by the boot_stage2 target
in the Raspberry Pi Pico SDK
*/
.flash_begin : {
__flash_binary_start = .;
} > FLASH
.boot2 : {
__boot2_start__ = .;
KEEP (*(.boot2))
__boot2_end__ = .;
} > FLASH
ASSERT(__boot2_end__ - __boot2_start__ == 256,
"ERROR: Pico second stage bootloader must be 256 bytes in size")
/* The second stage will always enter the image at the start of .text.
The debugger will use the ELF entry point, which is the _entry_point
symbol if present, otherwise defaults to start of .text.
This can be used to transfer control back to the bootrom on debugger
launches only, to perform proper flash setup.
*/
.text : {
__logical_binary_start = .;
KEEP (*(.vectors))
KEEP (*(.binary_info_header))
__binary_info_header_end = .;
KEEP (*(.reset))
/* TODO revisit this now memset/memcpy/float in ROM */
/* bit of a hack right now to exclude all floating point and time critical (e.g. memset, memcpy) code from
* FLASH ... we will include any thing excluded here in .data below by default */
*(.init)
/* Change for MicroPython... excluse gc.c, parse.c, vm.c from flash */
*(EXCLUDE_FILE(*libgcc.a: *libc.a: *lib_a-mem*.o *libm.a: *gc.c.obj *vm.c.obj *parse.c.obj) .text*)
*(.fini)
/* Pull all c'tors into .text */
*crtbegin.o(.ctors)
*crtbegin?.o(.ctors)
*(EXCLUDE_FILE(*crtend?.o *crtend.o) .ctors)
*(SORT(.ctors.*))
*(.ctors)
/* Followed by destructors */
*crtbegin.o(.dtors)
*crtbegin?.o(.dtors)
*(EXCLUDE_FILE(*crtend?.o *crtend.o) .dtors)
*(SORT(.dtors.*))
*(.dtors)
*(.eh_frame*)
. = ALIGN(4);
} > FLASH
.rodata : {
*(EXCLUDE_FILE(*libgcc.a: *libc.a:*lib_a-mem*.o *libm.a:) .rodata*)
. = ALIGN(4);
*(SORT_BY_ALIGNMENT(SORT_BY_NAME(.flashdata*)))
. = ALIGN(4);
} > FLASH
.ARM.extab :
{
*(.ARM.extab* .gnu.linkonce.armextab.*)
} > FLASH
__exidx_start = .;
.ARM.exidx :
{
*(.ARM.exidx* .gnu.linkonce.armexidx.*)
} > FLASH
__exidx_end = .;
/* Machine inspectable binary information */
. = ALIGN(4);
__binary_info_start = .;
.binary_info :
{
KEEP(*(.binary_info.keep.*))
*(.binary_info.*)
} > FLASH
__binary_info_end = .;
. = ALIGN(4);
/* End of .text-like segments */
__etext = .;
.ram_vector_table (COPY): {
*(.ram_vector_table)
} > RAM
.data : {
__data_start__ = .;
*(vtable)
*(.time_critical*)
/* remaining .text and .rodata; i.e. stuff we exclude above because we want it in RAM */
*(.text*)
. = ALIGN(4);
*(.rodata*)
. = ALIGN(4);
*(.data*)
. = ALIGN(4);
*(.after_data.*)
. = ALIGN(4);
/* preinit data */
PROVIDE_HIDDEN (__mutex_array_start = .);
KEEP(*(SORT(.mutex_array.*)))
KEEP(*(.mutex_array))
PROVIDE_HIDDEN (__mutex_array_end = .);
. = ALIGN(4);
/* preinit data */
PROVIDE_HIDDEN (__preinit_array_start = .);
KEEP(*(SORT(.preinit_array.*)))
KEEP(*(.preinit_array))
PROVIDE_HIDDEN (__preinit_array_end = .);
. = ALIGN(4);
/* init data */
PROVIDE_HIDDEN (__init_array_start = .);
KEEP(*(SORT(.init_array.*)))
KEEP(*(.init_array))
PROVIDE_HIDDEN (__init_array_end = .);
. = ALIGN(4);
/* finit data */
PROVIDE_HIDDEN (__fini_array_start = .);
*(SORT(.fini_array.*))
*(.fini_array)
PROVIDE_HIDDEN (__fini_array_end = .);
*(.jcr)
. = ALIGN(4);
/* All data end */
__data_end__ = .;
} > RAM AT> FLASH
.uninitialized_data (COPY): {
. = ALIGN(4);
*(.uninitialized_data*)
} > RAM
/* bss without zero init on startup */
.uninitialized_bss (NOLOAD): {
. = ALIGN(4);
*(.uninitialized_bss*)
} > RAM
/* Start and end symbols must be word-aligned */
.scratch_x : {
__scratch_x_start__ = .;
*(.scratch_x.*)
. = ALIGN(4);
__scratch_x_end__ = .;
} > SCRATCH_X AT > FLASH
__scratch_x_source__ = LOADADDR(.scratch_x);
.scratch_y : {
__scratch_y_start__ = .;
*(.scratch_y.*)
. = ALIGN(4);
__scratch_y_end__ = .;
} > SCRATCH_Y AT > FLASH
__scratch_y_source__ = LOADADDR(.scratch_y);
.bss : {
. = ALIGN(4);
__bss_start__ = .;
*(SORT_BY_ALIGNMENT(SORT_BY_NAME(.bss*)))
*(COMMON)
. = ALIGN(4);
__bss_end__ = .;
} > RAM
.heap (COPY):
{
__end__ = .;
end = __end__;
*(.heap*)
__HeapLimit = .;
} > RAM
/* .stack*_dummy section doesn't contains any symbols. It is only
* used for linker to calculate size of stack sections, and assign
* values to stack symbols later
*
* stack1 section may be empty/missing if platform_launch_core1 is not used */
/* by default we put core 0 stack at the end of scratch Y, so that if core 1
* stack is not used then all of SCRATCH_X is free.
*/
.stack1_dummy (COPY):
{
*(.stack1*)
} > SCRATCH_X
.stack_dummy (COPY):
{
*(.stack*)
} > SCRATCH_Y
.flash_end : {
__flash_binary_end = .;
} > FLASH
/* stack limit is poorly named, but historically is maximum heap ptr */
__StackLimit = ORIGIN(RAM) + LENGTH(RAM);
__StackOneTop = ORIGIN(SCRATCH_X) + LENGTH(SCRATCH_X);
__StackTop = ORIGIN(SCRATCH_Y) + LENGTH(SCRATCH_Y);
__StackOneBottom = __StackOneTop - SIZEOF(.stack1_dummy);
__StackBottom = __StackTop - SIZEOF(.stack_dummy);
/* Define start and end of GC heap */
__GcHeapStart = __bss_end__;
__GcHeapEnd = __StackLimit;
PROVIDE(__stack = __StackTop);
/* Check if data + heap + stack exceeds RAM limit */
ASSERT(__StackLimit >= __HeapLimit, "region RAM overflowed")
/* Check GC heap is at least 128 KB */
/* On a RP2040 using all SRAM this should always be the case. */
ASSERT((__GcHeapEnd - __GcHeapStart) > 128*1024, "GcHeap is too small")
ASSERT( __binary_info_header_end - __logical_binary_start <= 256, "Binary info must be in first 256 bytes of the binary")
/* todo assert on extra code */
}
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