Add dedicated section for pdm buffer (#13)

* Add dedicated section for pdm buffer

Author: pennam

targets/TARGET_STM/TARGET_STM32H7/TARGET_STM32H747xI/TARGET_PORTENTA_H7_M4/TOOLCHAIN_GCC_ARM/STM32H747xI.ld

@@ -30,7 +30,8 @@ MEMORY
 {
   RAM (xrw)                     : ORIGIN = RAM_START + 0x298, LENGTH = RAM_SIZE - 0x298
   OPENAMP_RSC_TAB (rwx)         : ORIGIN = 0x38000000, LENGTH = 1K
-  OPEN_AMP_SHMEM (rwx)          : ORIGIN = 0x38000400, LENGTH = 63K
+  OPEN_AMP_SHMEM (rwx)          : ORIGIN = 0x38000400, LENGTH = 62K
+  /*PDM_MEM (rwx)                 : ORIGIN = 0x3800FC00, LENGTH = 1K Reserved for PDM and M7 */
   FLASH (rx)                    : ORIGIN = MBED_APP_START, LENGTH = MBED_APP_SIZE
 }
  __OPENAMP_region_start__  = ORIGIN(OPEN_AMP_SHMEM);

targets/TARGET_STM/TARGET_STM32H7/TARGET_STM32H747xI/TARGET_PORTENTA_H7_M7/TOOLCHAIN_GCC_ARM/STM32H747xI.ld

@@ -33,7 +33,8 @@ MEMORY
   RAM (xrw)                     : ORIGIN = RAM_START + 0x298, LENGTH = RAM_SIZE - 0x298
   RAM_D2 (xrw)                  : ORIGIN = 0x30000000, LENGTH = 288K
   OPENAMP_RSC_TAB (rwx)         : ORIGIN = 0x38000000, LENGTH = 1K
-  OPEN_AMP_SHMEM (rwx)          : ORIGIN = 0x38000400, LENGTH = 63K
+  OPEN_AMP_SHMEM (rwx)          : ORIGIN = 0x38000400, LENGTH = 62K
+  PDM_MEM (xrw)                 : ORIGIN = 0x3800FC00, LENGTH = 1k
   FLASH (rx)                    : ORIGIN = MBED_APP_START, LENGTH = MBED_APP_SIZE
 }
  __OPENAMP_region_start__  = ORIGIN(OPEN_AMP_SHMEM);
@@ -192,6 +193,11 @@ SECTIONS
         *(.resource_table)
     } >OPENAMP_RSC_TAB  AT > FLASH
 
+    .pdm_section (NOLOAD) : {
+        . = ABSOLUTE(0x3800FC00);
+        *(.pdm_buffer)
+    } > PDM_MEM
+
     /* .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 */