M2351: Re-build default secure image/gateway library to favor Pelion application

In this new memory partition, secure program is most simplified and non-secure program can make most use of memory for its large application like Pelion:

-   Flash (512KiB in total): 64KiB for secure and 448KiB for nonsecure.
-   SRAM (96KiB in total): 8KiB for secure and 88KiB for nonsecure.

Besides, to make secure program fit into 8KiB:

-   Decrease boot stack size to 0x600 bytes
-   Remove serial support

targets/TARGET_NUVOTON/TARGET_M2351/TARGET_M23_NS/TARGET_NU_PFM_M2351_NPSA_NS/TARGET_NU_PREBUILD_SECURE/README.md

@@ -1,14 +1,15 @@
-The M2351 is a TrustZone target that requires two codes: secure and nonsecure. Secure code runs first to set up the secure environment and then brings up the nonsecure code. `NuMaker-mbed-TZ-secure-example.hex` is the pre-built secure image, and `cmse_lib.o` is its accompanying
-secure gateway library, which exports secure functions to nonsecure code. It is built from the [non-PSA secure code template](https://github.com/OpenNuvoton/NuMaker-mbed-TZ-secure-example). Because secure and nonsecure code may start at an address other than `0x0`, we have chosen `.hex` rather than `.bin` as the output format.
+The M2351 is a TrustZone target that requires two programs: secure and nonsecure.
+Secure program runs first to set up the secure environment and then brings up the nonsecure program. `NuMaker-mbed-TZ-secure-example.hex` is the pre-built secure image, and `cmse_lib.o` is its accompanying secure gateway library, which exports secure functions to nonsecure program.
+It is built from the [non-PSA secure program template](https://github.com/OpenNuvoton/NuMaker-mbed-TZ-secure-example). Because secure program and nonsecure program may start at an address other than `0x0`, we have chosen `.hex` rather than `.bin` as the output format.
 
 ## Hardware partition
 
-On TrustZone targets, you need to partition the hardware first for secure code to run on secure world and nonsecure code to run on nonsecure world.
+On TrustZone targets, you need to partition the hardware first for secure program to run on secure world and nonsecure program to run on nonsecure world.
 
-The pre-built secure code has the following hardware partition:
+The pre-built secure program will set up the following hardware partition:
 
-- Flash (512KiB in total): 256KiB for secure and 256KiB for nonsecure.
-- SRAM (96KiB in total): 32KiB for secure and 64KiB for nonsecure.
+- Flash (512KiB in total): 64KiB for secure and 448KiB for nonsecure.
+- SRAM (96KiB in total): 8KiB for secure and 88KiB for nonsecure.
 - Peripherals: Most are configured to nonsecure except the following, which are hardwired or reserved:
     - **SYS/CLK** hardwired to secure. Accessible to nonsecure through a secure gateway.
     - **FMC** hardwired to secure. Accessible to nonsecure through a secure gateway.
@@ -20,13 +21,22 @@ The pre-built secure code has the following hardware partition:
     - **PDMA1** configured to nonsecure. Implements nonsecure asynchronous transfer.
     - **TRNG** configured to secure. Accessible to nonsecure through a secure gateway.
 
-## Pre-built secure code files
+In this memory partition, secure program is the most simplified.
+Then non-secure program can make use of the most memory available for its large application like Pelion.
+
+To regenerate the default secure program, in [non-PSA secure program template](https://github.com/OpenNuvoton/NuMaker-mbed-TZ-secure-example), run:
+
+```sh
+$ mbed compile -m NU_PFM_M2351_NPSA_S -t ARMC6 --profile release
+```
+
+## Pre-built secure program files
 
 -   NuMaker-mbed-TZ-secure-example.hex
     Pre-built secure image generated in non-PSA secure target build and to combine with non-secure image in non-PSA non-secure target post-build
 -   cmse_lib.o
-    Pre-built secure gateway library generated in non-PSA secure target build and to link with non-secure code in non-PSA non-secure target build
+    Pre-built secure gateway library generated in non-PSA secure target build and to link with non-secure program in non-PSA non-secure target build
 
 ## Reference
 
-Please refer to the [non-PSA secure code template](https://github.com/OpenNuvoton/NuMaker-mbed-TZ-secure-example) for details.
+Please refer to the [non-PSA secure program template](https://github.com/OpenNuvoton/NuMaker-mbed-TZ-secure-example) for details.

targets/targets.json

@@ -8878,25 +8878,29 @@
         "components_add": ["FLASHIAP"],
         "post_binary_hook": {"function": "M2351Code.merge_secure"},
         "secure_image_filename": "NuMaker-mbed-TZ-secure-example.hex",
-        "mbed_rom_start"        : "0x10040000",
-        "mbed_rom_size"         : "0x40000",
-        "mbed_ram_start"        : "0x30008000",
-        "mbed_ram_size"         : "0x10000"
+        "mbed_rom_start"        : "0x10010000",
+        "mbed_rom_size"         : "0x70000",
+        "mbed_ram_start"        : "0x30002000",
+        "mbed_ram_size"         : "0x16000"
     },
     "NU_PFM_M2351_NPSA_S": {
+        "overrides": {
+            "boot-stack-size"   : "0x600"
+        },
         "inherits": ["NU_PFM_M2351"],
         "core": "Cortex-M23",
         "trustzone": true,
         "extra_labels_add": [
             "M23_S"
         ],
+        "device_has_remove": ["SERIAL", "SERIAL_ASYNCH", "SERIAL_FC", "STDIO_MESSAGES"],
         "components_add": ["FLASHIAP"],
         "deliver_to_target": "NU_PFM_M2351_NPSA_NS",
         "delivery_dir": "TARGET_NUVOTON/TARGET_M2351/TARGET_M23_NS/TARGET_NU_PFM_M2351_NPSA_NS/TARGET_NU_PREBUILD_SECURE",
         "mbed_rom_start"        : "0x0",
-        "mbed_rom_size"         : "0x40000",
+        "mbed_rom_size"         : "0x10000",
         "mbed_ram_start"        : "0x20000000",
-        "mbed_ram_size"         : "0x8000"
+        "mbed_ram_size"         : "0x2000"
     },
     "NUMAKER_M252KG": {
         "core": "Cortex-M23",