ckormanyos · ckormanyos · Apr 1, 2025 · Apr 1, 2025 · Apr 1, 2025
diff --git a/readme.md b/readme.md
@@ -66,15 +66,15 @@ In this way the project exhibits a high level of portability.
 
 ## Supported Targets in the Reference Application
 
-The reference application supports the following targets:
+The reference application supports the following targets (in alpha-numeric order):
 
 | Target name (as used in build command) | Target Description                                          | *(breadboard) |
 | -------------------------------------- | ----------------------------------------------------------- | ------------- |
-| `avr`                                  | MICROCHIP(R) [former ATMEL(R)] AVR(R) ATmega328P            | X             |
+| `am335x`                               | BeagleBone with Texas Instruments(R) AM335x ARM(R) A8       |               |
 | `atmega2560`                           | MICROCHIP(R) [former ATMEL(R)] AVR(R) ATmega2560            |               |
 | `atmega4809`                           | MICROCHIP(R) [former ATMEL(R)] AVR(R) ATmegax4809           | X             |
-| `am335x`                               | BeagleBone with Texas Instruments(R) AM335x ARM(R) A8       |               |
-| `bcm2835_raspi_b`                      | RaspberryPi(R) Zero with ARM1176-JZFS(TM)                   |               |
+| `avr` (as used in the book)            | MICROCHIP(R) [former ATMEL(R)] AVR(R) ATmega328P            | X             |
+| `bcm2835_raspi_b`                      | RaspberryPi(R) Zero with ARM1176-JZFS(TM)                   | X             |
 | `Debug`/`Release`                      | PC on `Win*` via MSVC x64 compiler `Debug`/`Release`        |               |
 | `host`                                 | PC/Workstation on `Win*`/`mingw64`/`*nix` via host compiler |               |
 | `lpc11c24`                             | NXP(R) OM13093 LPC11C24 board ARM(R) Cortex(R)-M0+          |               |
@@ -359,17 +359,23 @@ any additional libraries for these projects
 (other than those that are ordinarily installed
 during the standard installation of ATMEL Studio).
 
-## Target Details
+## Details on Selected Target
 
 Target details including startup code and linker definition files can
 be found in the [ref_app/target](./ref_app/target) directory
 and its subdirectories. There are individual subdirectories for
 each supported target microcontroller system.
 
-The MICROCHIP(R) [former ATMEL(R)] AVR(R) configuration
-called `target avr` runs
-on a classic ARDUINO(R) compatible board.
-The program toggles the yellow LED on `portb.5`.
+The ARM(R) A8 configuration (called `target am335x`) runs on the BeagleBone
+board (black edition). For the white edition, the CPU clock needs to be reduced
+from $900~\text{MHz}$ to something like $600~\text{MHz}$. This project creates a bare-metal program
+for the BeagleBone that runs independently from any kind of `*nix` distro on
+the board. Our program is designed to boot the BeagleBone from a raw binary file
+called _MLO_ stored on a FAT32 SDHC microcard. The binary file includes a
+special boot header comprised of two 32-bit integers. The program is loaded
+from SD-card into RAM memory and subsequently executed. When switching on
+the BeagleBone black, the boot button (S2) must be pressed while powering
+up the board. The program toggles the first user LED (LED1 on `port1.21`).
 
 The MICROCHIP(R) [former ATMEL(R)] AVR(R) configuration
 called `target atmega2560` runs
@@ -389,70 +395,10 @@ on an ARDUINO(R) EVERY compatible board clocked
 with the internal resonator at $20~\text{MHz}$.
 The program toggles the yellow LED on `porte.2` (i.e., `D5`).
 
-The Espressif (`target xtensa32`) port for NodeMCU ESP32
-uses a subset of the
-[Espressif SDK](https://github.com/espressif/esp-idf)
-to run the reference application.
-This somewhat unconventional implementation configures
-$1$ single OS task running exclusively on $1$ CPU core only.
-Additional reductions in code/memory size(s) have been accomplished
-via selective stubbing of library functions.
-
-The Espressif (`target xtensa_esp32_s3`) port for NodeMCU ESP32-S3
-features a bare-metal startup _without_ using any of the SDK.
-The bare-metal startup was taken from the work of
-[Chalandi/Baremetal_esp32s3_nosdk](https://github.com/Chalandi/Baremetal_esp32s3_nosdk).
-The multicore system first boots core0 which subsequently
-starts up core1 and also starts up the RISC-V-ULP coprocessor core.
-Blinky runs in the standard `ref_app`
-on core0 toggling `port7` while an endless timer loop on core1
-toggles `port6`. These LED ports togle in near unison
-at the normal blinky feequency of $\frac{1}{2}~\text{Hz}$.
-The RISC-V-ULP coprocessor performs an LED dimming
-show on `port17` at a randomly chosen frequency
-that is asynchronous to the regular blinky show.
-Self-procured LEDs and resistors need to be fitted externally
-on the port pins in order to observe blinking and dimming
-on this particular board.
-
-The NXP(R) OM13093 LPC11C24 board ARM(R) Cortex(R)-M0+ configuration
-called `target lpc11c24` toggles the LED on `port0.8`.
-
-The ARM(R) Cortex(R)-M3 configuration (called `target stm32f100`) runs on
-the STM32VL-DISCOVERY board commercially available from ST Microelectronics(R).
-The program toggles the blue LED on `portc.8`.
-
-The second ARM(R) Cortex(R)-M3 configuration (called `target stm32l100c`)
-runs on the STM32L100-DISCOVERY board commercially available from
-ST Microelectronics(R). The program toggles the blue LED on `portc.8`.
-
-The third ARM(R) Cortex(R)-M3 configuration (called `target stm32l152`)
-runs on the STM32L152C-DISCOVERY board commercially available from
-ST Microelectronics(R). The program toggles the blue LED on `portb.6`.
-
-The first ARM(R) Cortex(R)-M4F configuration (called `target stm32f407`) runs on
-the STM32F4-DISCOVERY board commercially available from ST Microelectronics(R).
-The program toggles the blue LED on `portd.15`.
-
-Another ARM(R) Cortex(R)-M4F configuration (called `target stm32f446`) runs on
-the STM32F446-NUCLEO-64 board commercially available from ST Microelectronics(R).
-The program toggles the green LED on `porta.5`.
-An Ozone debug file is supplied for this system for those interested.
-
-The first ARM(R) Cortex(R)-M7 configuration (called `target stm32h7a3`) runs on
-the STM32H7A3-NUCLEO-144 board commercially available from ST Microelectronics(R).
-The program toggles the green LED on `portb.0`.
-
-The ARM(R) A8 configuration (called `target am335x`) runs on the BeagleBone
-board (black edition). For the white edition, the CPU clock needs to be reduced
-from $900~\text{MHz}$ to something like $600~\text{MHz}$. This project creates a bare-metal program
-for the BeagleBone that runs independently from any kind of `*nix` distro on
-the board. Our program is designed to boot the BeagleBone from a raw binary file
-called _MLO_ stored on a FAT32 SDHC microcard. The binary file includes a
-special boot header comprised of two 32-bit integers. The program is loaded
-from SD-card into RAM memory and subsequently executed. When switching on
-the BeagleBone black, the boot button (S2) must be pressed while powering
-up the board. The program toggles the first user LED (LED1 on `port1.21`).
+The MICROCHIP(R) [former ATMEL(R)] AVR(R) configuration
+called `target avr` (as used in the book) runs
+on a classic ARDUINO(R) compatible board.
+The program toggles the yellow LED on `portb.5`.
 
 The ARM(R) 1176-JZF-S configuration (called `target bcm2835_raspi_b`) runs on the
 RaspberryPi(R) Zero (PiZero) single core controller.
@@ -469,33 +415,65 @@ config.txt, all described on internet. A complete set of
 running the bare-metal reference application are included in this repo.
 The program toggles the GPIO status LED  at GPIO index `0x47`.
 
+The NXP(R) OM13093 LPC11C24 board ARM(R) Cortex(R)-M0+ configuration
+called `target lpc11c24` toggles the LED on `port0.8`.
+
+Target `nxp_imxrt1062` runs on the Teensy 4.0 board from Spark Fun.
+The orange user-LED is toggled.
+
+The `riscvfe310` target utilizes the SiFive RISC-V FE310 SoC
+on Spark Fun's commercially available _Red_ _Thing_ _Plus_ Board.
+The blue LED on port `GPIO0.5` is toggled.
+
 The `rpi_pico_rp2040` target configuration employs the
 RaspberryPi(R) Pico RP2040 with dual-core ARM(R) Cortex(R)-M0+
 clocked at $133~\text{MHz}$. The low-level startup boots through
-core0. Core0 then starts up core1 (via a specific protocol).
-Core1 subsequently carries out the blinky application,
-while core0 enters an endless, idle loop.
-Ozone debug files are supplied for this system for those interested.
-Reverse engineering of the complicated (and scantly documented)
-dual-core startup originated in and have been taken from (with many thanks)
-from the `Blinky_Pico_dual_core_nosdk`
-[repo](https://github.com/Chalandi/Blinky_Pico_dual_core_nosdk).
+core0 which then starts up core1 via specific protocol.
+Core1 carries out the blinky application while core0 enters an endless,
+idle loop. Ozone debug files are supplied for this system
+for those interested. Reverse engineering of the complicated
+and scantly documented dual-core startup originated in
+and have been taken (with many thanks) from the
+[`Chalandi/Blinky_Pico_dual_core_nosdk`](https://github.com/Chalandi/Blinky_Pico_dual_core_nosdk).
+repository.
 
 The `rpi_pico2_rp2350` target configuration employs the
 RaspberryPi(R) Pico2 RP2350 with dual-core ARM(R) Cortex(R)-M33
 clocked at $150~\text{MHz}$. It has essentially the same boot
 structure as the `2040`. Similarly the dual-core startup was
-pioneered by the efforts revealed in the modernized `Blinky_Pico2_dual_core_nosdk`
-[repo](https://github.com/Chalandi/Blinky_Pico2_dual_core_nosdk).
+pioneered by the efforts revealed in the modernized
+[`Chalandi/Blinky_Pico2_dual_core_nosdk`](https://github.com/Chalandi/Blinky_Pico2_dual_core_nosdk).
+repository.
+
+The ARM(R) Cortex(R)-M3 configuration (called `target stm32f100`) runs on
+the STM32VL-DISCOVERY board commercially available from ST Microelectronics(R).
+The program toggles the blue LED on `portc.8`.
+
+The first ARM(R) Cortex(R)-M4F configuration (called `target stm32f407`) runs on
+the STM32F4-DISCOVERY board commercially available from ST Microelectronics(R).
+The program toggles the blue LED on `portd.15`.
+
+Another ARM(R) Cortex(R)-M4F configuration (called `target stm32f446`) runs on
+the STM32F446-NUCLEO-64 board commercially available from ST Microelectronics(R).
+The program toggles the green LED on `porta.5`.
+An Ozone debug file is supplied for this system for those interested.
+
+The first ARM(R) Cortex(R)-M7 configuration (called `target stm32h7a3`) runs on
+the STM32H7A3-NUCLEO-144 board commercially available from ST Microelectronics(R).
+The program toggles the green LED on `portb.0`.
+
+The second ARM(R) Cortex(R)-M3 configuration (called `target stm32l100c`)
+runs on the STM32L100-DISCOVERY board commercially available from
+ST Microelectronics(R). The program toggles the blue LED on `portc.8`.
+
+The third ARM(R) Cortex(R)-M3 configuration (called `target stm32l152`)
+runs on the STM32L152C-DISCOVERY board commercially available from
+ST Microelectronics(R). The program toggles the blue LED on `portb.6`.
 
 The `target v850es_fx2` implementation uses a classic Renesas(R) V850es/Fx2 core.
 The upd703231 microcontroller derivative on an F-Line _Drive_ _It_
 starter kit is used.
 
-The `riscvfe310` target utilizes the SiFive RISC-V FE310 SoC
-on Spark Fun's commercially available _Red_ _Thing_ _Plus_ Board.
-The blue LED on port `GPIO0.5` is toggled.
-
 The adaption for `wch_ch32v307` runs on the WCH CH32v307 board.
 It uses the RISC-V CH32v307 microcontroller from
 Nanjing Qinheng Microelectronics Co., Ltd.
@@ -505,8 +483,31 @@ The similar adaption `wch_ch32v307_llvm` is essentially
 the same except it uses an LLVM RISC-V toolchain
 instead of GCC RISC-V.
 
-Target `nxp_imxrt1062` runs on the Teensy 4.0 board from Spark Fun.
-The orange user-LED is toggled.
+The Espressif (`target xtensa_esp32_s3`) port for NodeMCU ESP32-S3
+features a bare-metal startup _without_ using any of the SDK.
+The bare-metal startup was taken from the work of
+[Chalandi/Baremetal_esp32s3_nosdk](https://github.com/Chalandi/Baremetal_esp32s3_nosdk).
+The multicore system first boots core0 which subsequently
+starts up core1 and also starts up the RISC-V-ULP coprocessor core.
+Blinky runs in the standard `ref_app`
+on core0 toggling `port7` while an endless timer loop on core1
+toggles `port6`. These LED ports togle in near unison
+at the normal blinky feequency of $\frac{1}{2}~\text{Hz}$.
+The RISC-V-ULP coprocessor performs an LED dimming
+show on `port17` at a randomly chosen frequency
+that is asynchronous to the regular blinky show.
+Self-procured LEDs and resistors need to be fitted externally
+on the port pins in order to observe blinking and dimming
+on this particular board.
+
+The Espressif (`target xtensa32`) port for NodeMCU ESP32
+uses a subset of the
+[Espressif SDK](https://github.com/espressif/esp-idf)
+to run the reference application.
+This somewhat unconventional implementation configures
+$1$ single OS task running exclusively on $1$ CPU core only.
+Additional reductions in code/memory size(s) have been accomplished
+via selective stubbing of library functions.
 
 For other compatible boards, feel free contact me directly or submit
 an issue requesting support for your desired target system.

diff --git a/ref_app/target/micros/xtensa_esp32_s3/startup/Std/StdLib.cpp b/ref_app/target/micros/xtensa_esp32_s3/startup/Std/StdLib.cpp
@@ -29,26 +29,26 @@
 
 extern "C" {
 
-typedef   signed long long DItype  __attribute__((mode (DI)));
-typedef unsigned long long UDItype __attribute__((mode (DI)));
-typedef unsigned int       USItype __attribute__((mode (SI)));
+using DItype  =   signed long long;
+using UDItype = unsigned long long;
+using USItype = unsigned int;
 
-extern int __builtin_clzll(unsigned long long);
+extern auto __builtin_clzll(unsigned long long) -> int;
 
-#define DWtype  DItype
-#define UDWtype UDItype
-#define UWtype  USItype
+using DWtype  = DItype;
+using UDWtype = UDItype;
+using UWtype  = USItype;
 
-UDWtype __udivdi3    (UDWtype n, UDWtype d);
-UDWtype __udivmoddi4 (UDWtype n, UDWtype d, UDWtype *rp);
-UDWtype __umoddi3    (UDWtype u, UDWtype v);
+auto __udivdi3    (UDWtype n, UDWtype d)              -> UDWtype;
+auto __udivmoddi4 (UDWtype n, UDWtype d, UDWtype *rp) -> UDWtype;
+auto __umoddi3    (UDWtype u, UDWtype v)              -> UDWtype;
 
-UDWtype __udivdi3 (UDWtype n, UDWtype d)
+auto __udivdi3 (UDWtype n, UDWtype d) -> UDWtype
 {
   return __udivmoddi4 (n, d, (UDWtype *) 0);
 }
 
-UDWtype __umoddi3 (UDWtype u, UDWtype v)
+auto __umoddi3 (UDWtype u, UDWtype v) -> UDWtype
 {
   UDWtype w;
 
@@ -57,7 +57,7 @@ UDWtype __umoddi3 (UDWtype u, UDWtype v)
   return w;
 }
 
-UDWtype __udivmoddi4 (UDWtype n, UDWtype d, UDWtype *rp)
+auto __udivmoddi4 (UDWtype n, UDWtype d, UDWtype *rp) -> UDWtype
 {
   UDWtype q = 0, r = n, y = d;
   UWtype lz1, lz2, i, k;
@@ -136,7 +136,7 @@ UDWtype __udivmoddi4 (UDWtype n, UDWtype d, UDWtype *rp)
 #pragma GCC diagnostic ignored "-Wcast-align"
 #endif
 
-void* memset(void* str, int c, size_t n)
+auto memset(void* str, int c, size_t n) -> void*
 {
   std::uint8_t* ptr { reinterpret_cast<std::uint8_t*>(str) };
 
@@ -180,7 +180,7 @@ void* memset(void* str, int c, size_t n)
   return str;
 }
 
-void* memcpy (void* dest, const void* src, size_t n)
+auto memcpy (void* dest, const void* src, size_t n) -> void*
 {
         std::uint8_t* d { reinterpret_cast<std::uint8_t*>(dest) };
   const std::uint8_t* s { reinterpret_cast<const uint8_t*>(src) };

diff --git a/ref_app/target/micros/xtensa_esp32_s3/startup/Std/core-isa.h b/ref_app/target/micros/xtensa_esp32_s3/startup/Std/core-isa.h
@@ -1,3 +1,9 @@
+///////////////////////////////////////////////////////////////////////////////
+//  Copyright Christopher Kormanyos 2025.
+//  Distributed under the Boost Software License,
+//  Version 1.0. (See accompanying file LICENSE_1_0.txt
+//  or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
 
 // Originally from (but slightly modified from):
 

diff --git a/ref_app/target/micros/xtensa_esp32_s3/startup/Std/ieee754-sf.S b/ref_app/target/micros/xtensa_esp32_s3/startup/Std/ieee754-sf.S
@@ -1,5 +1,12 @@
+/******************************************************************************************
+//  Copyright Christopher Kormanyos 2025.
+//  Distributed under the Boost Software License,
+//  Version 1.0. (See accompanying file LICENSE_1_0.txt
+//  or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+******************************************************************************************/
 
-// Originally from:
+// Originally from (but slightly modified from):
 
 /* IEEE-754 single-precision functions for Xtensa
    Copyright (C) 2006-2025 Free Software Foundation, Inc.
@@ -272,7 +279,8 @@ __addsf3:
 
   /* Subtraction */
 __subsf3_aux:
-
+.align 4
+
   /* Handle NaNs and Infinities.  (This code is placed before the
      start of the function just to keep it in range of the limited
      branch displacements.)  */
@@ -438,7 +446,7 @@ __subsf3:
   movi  a2, 0
   leaf_return
 
-.Lsub_borrow:  
+.Lsub_borrow:
   /* The subtraction has underflowed into the exponent field, so the
      value needs to be renormalized.  Shift the mantissa left as
      needed to remove any leading zeros and adjust the exponent
@@ -502,12 +510,12 @@ __subsf3:
 
 #ifdef L_mulsf3
 
-  /* Multiplication */
+/* Multiplication */
 #if !XCHAL_HAVE_MUL16 && !XCHAL_HAVE_MUL32 && !XCHAL_HAVE_MAC16
 #define XCHAL_NO_MUL 1
 #endif
 
-  .literal_position
+.literal_position
 __mulsf3_aux:
 
   /* Handle unusual cases (zeros, subnormals, NaNs and Infinities).

diff --git a/ref_app/target/micros/xtensa_esp32_s3/startup/Std/lib1funcs.S b/ref_app/target/micros/xtensa_esp32_s3/startup/Std/lib1funcs.S
@@ -1,5 +1,12 @@
-
-// Originally from:
+/******************************************************************************************
+//  Copyright Christopher Kormanyos 2025.
+//  Distributed under the Boost Software License,
+//  Version 1.0. (See accompanying file LICENSE_1_0.txt
+//  or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+******************************************************************************************/
+
+// Originally from (but slightly modified from):
 
 /* Assembly functions for the Xtensa version of libgcc1.
    Copyright (C) 2001-2025 Free Software Foundation, Inc.

diff --git a/ref_app/target/micros/xtensa_esp32_s3/startup/boot.S b/ref_app/target/micros/xtensa_esp32_s3/startup/boot.S
@@ -6,7 +6,7 @@
 //
 ******************************************************************************************/
 
-/* Originally from: */
+/* Originally from (but slightly modified from): */
 /******************************************************************************************
   Filename    : boot.S