Custom board e73-tbb sort of works.

code/parasite/boards/e73-tbb.json

@@ -1,7 +1,7 @@
 {
   "build": {
     "arduino":{
-      "ldscript": "nrf52_xxaa.ld"
+      "ldscript": "nrf52832_s132_v6.ld"
     },
     "core": "nRF5",
     "cpu": "cortex-m4",

code/parasite/ldscripts/nrf52832_s132_v6.ld

@@ -0,0 +1,40 @@
+/* Linker script to configure memory regions. */
+/* Source: https://raw.githubusercontent.com/adafruit/Adafruit_nRF52_Arduino/master/cores/nRF5/linker/nrf52832_s132_v6.ld */
+
+SEARCH_DIR(.)
+GROUP(-lgcc -lc -lnosys)
+
+MEMORY
+{
+  FLASH (rx)     : ORIGIN = 0x26000, LENGTH = 0x6D000 - 0x26000
+
+  /* SRAM required by S132 depend on
+   * - Attribute Table Size
+   * - Vendor UUID count
+   * - Max ATT MTU
+   * - Concurrent connection peripheral + central + secure links
+   * - Event Len, HVN queue, Write CMD queue
+   */
+  RAM (rwx) :  ORIGIN = 0x20003600, LENGTH = 0x20010000 - 0x20003600
+}
+
+SECTIONS
+{
+  . = ALIGN(4);
+  .svc_data :
+  {
+    PROVIDE(__start_svc_data = .);
+    KEEP(*(.svc_data))
+    PROVIDE(__stop_svc_data = .);
+  } > RAM
+
+  .fs_data :
+  {
+    PROVIDE(__start_fs_data = .);
+    KEEP(*(.fs_data))
+    PROVIDE(__stop_fs_data = .);
+  } > RAM
+} INSERT AFTER .data;
+
+/* TODO(rbaron): This should be failing but it's not. Maybe it's loading it from somewhere else? */
+INCLUDE "nrf52_common.ld"

code/parasite/platformio.ini

@@ -8,15 +8,11 @@
 ; Please visit documentation for the other options and examples
 ; https://docs.platformio.org/page/projectconf.html
 
-; [env:adafruit_feather_nrf52832]
 [env:e73-tbb]
 platform = nordicnrf52
-board = adafruit_feather_nrf52832
-; board = e73-tbb
+; board = adafruit_feather_nrf52832
+; Additionally, I had to force use_adafruit = True in platforms/nordicnrf52/builder/main.py
+board = e73-tbb
 framework = arduino
 build_flags = -DNRF52 -DS132 -DNRF51_S132
-; upload_port = /dev/cu.usbserial-14330
-; debug_tool = jlink
-; protocol = nrfutil
-; lib_deps =
-;   mbed-glimwormbeacons/SEGGER_RTT2 @ 0.0.0+sha.a7800e894aaf
+board_build.ldscript = ./ldscripts/nrf52832_s132_v6.ld

resources.md

@@ -51,3 +51,48 @@ Upgrading target on /dev/cu.usbserial-14330 with DFU package /Users/rbaron/dev/p
 Activating new firmware
 Device programmed.
 ```
+
+# Linking
+In [platformio-core/tools/pioplatform.py](https://github.com/platformio/platformio-core/blob/9c20ab81cb68f1ffb7a8cac22ce95c4c797643ec/platformio/builder/tools/pioplatform.py#L130):
+```Python
+if "build.ldscript" in board_config:
+    env.Replace(LDSCRIPT_PATH=board_config.get("build.ldscript"))
+```
+In [platformio-core/platformio.py](https://github.com/platformio/platformio-core/blob/9c20ab81cb68f1ffb7a8cac22ce95c4c797643ec/platformio/builder/tools/platformio.py#L65):
+```Python
+# append into the beginning a main LD script
+if env.get("LDSCRIPT_PATH") and not any("-Wl,-T" in f for f in env["LINKFLAGS"]):
+    env.Prepend(LINKFLAGS=["-T", env.subst("$LDSCRIPT_PATH")])
+```
+The `-T` flag expects a path to a linker script, as per [`ld` docs](https://ftp.gnu.org/old-gnu/Manuals/ld-2.9.1/html_chapter/ld_3.html).
+
+Frameworks, such as the `nordicnrf52`, contain [boards definitions](https://github.com/platformio/platform-nordicnrf52/blob/develop/boards/adafruit_feather_nrf52832.json#L4) that specify the `ldscript`.
+
+1. For the [adafruit_feather_nrf52832](https://github.com/platformio/platform-nordicnrf52/blob/develop/boards/adafruit_feather_nrf52832.json#L4) board, we have:
+
+```
+"arduino":{
+  "ldscript": "nrf52832_s132_v6.ld"
+},
+```
+Which is defined [here](https://github.com/adafruit/Adafruit_nRF52_Arduino/blob/master/cores/nRF5/linker/nrf52832_s132_v6.ld).
+
+2. For the [nrf52_dk](https://github.com/platformio/platform-nordicnrf52/blob/develop/boards/nrf52_dk.json#L4), we have:
+```
+"arduino":{
+  "ldscript": "nrf52_xxaa.ld"
+},
+```
+Which is the most common linker script, and is part of the nordic official SDK, it seems, available [here](https://github.com/NordicSemiconductor/nrfx/blob/master/mdk/nrf52_xxaa.ld). For reference, check out the linker for the [Adafruit nRF52 Bootloader](https://github.com/adafruit/Adafruit_nRF52_Bootloader/blob/master/linker/nrf52.ld). Here you can see the [memory map](https://learn.adafruit.com/bluefruit-nrf52-feather-learning-guide/hathach-memory-map) of the nRF52 Feather.
+
+## Same platform, different framework
+Both the Feather nRF52832 and the Generic boards above point to the same platform, the [nordicnrf52](). Inside this platorm, there's a switch for selecting which framework to use, based on the board name, [here](https://github.com/platformio/platform-nordicnrf52/blob/develop/platform.py#L38):
+```Python
+if self.board_config(board).get("build.bsp.name",
+                                            "nrf5") == "adafruit":
+                self.frameworks["arduino"][
+                    "package"] = "framework-arduinoadafruitnrf52"
+```
+
+### Memory layout
+The [SoftDevice S132 spec](https://infocenter.nordicsemi.com/index.jsp?topic=%2Fsds_s112%2FSDS%2Fs1xx%2Fmem_usage%2Fmem_resource_map_usage.html&anchor=mem_resource_map_usage) specifies the layout as the soft device begins at addr 0x0 and the application code comes after it, at the address `APP_CODE_BASE`.