Swatantra-66 opened a new pull request, #20623:
URL: https://github.com/apache/nuttx/pull/20623
## Summary
This PR migrates the legacy monospaced `README.txt` for the **PJRC Teensy
3.x** development boards (NXP/Freescale Kinetis MK20DX256VLH7 / MK20DX128VLH5
MCU) into standard Sphinx rST documentation format in `index.rst`, removing the
`.. include:: README.txt :literal:` raw inclusion stub and deleting the legacy
`README.txt`.
Part of **Issue #11077** (*Documentation: port remaining README.txt in
platforms*) and **Issue #15737** (*NuttX-13.0.0 Release Notes*).
### Key Contents & Additions:
1. **Overview & MCU Hardware Specifications**:
- 32-bit ARM Cortex-M4 running at 72 MHz (overclockable up to 96 MHz via
`CONFIG_TEENSY_3X_OVERCLOCK=y`).
- 256 KB Flash memory, 64 KB SRAM, on-chip PLL, and 16 MHz external
crystal (PTA18/PTA19).
- Onboard Nuvoton Mini54TAN processor running PJRC's proprietary HalfKay
USB bootloader.
2. **Teensy 3.0 vs. Teensy 3.1 / 3.2 Hardware Comparison**:
- Comprehensive comparative table detailing processor cores, rated
speeds, SRAM, Flash memory, 5V tolerance, and linker script mapping
(`mk20dx128vlh5.ld` vs. `mk20dx256vlh7.ld`).
3. **Operating Voltage & 5V Tolerance Warnings**:
- Prominently highlights that while digital I/O pins on Teensy 3.1/3.2
are 5V tolerant, analog inputs (A10, A11, AREF, and ADC reference) and **all**
pins on the Teensy 3.0 are strictly **3.3V maximum**.
4. **Pin Mapping & Serial Console Tables**:
- Dedicated onboard hardware signals: Mini54TAN bootloader pins
(`PTA0-PTA3`, `PTB1-PTB2`), crystal (`PTA18/PTA19`), and user LED (`PTC5`).
- Full serial console pinout table covering `UART0`, `UART1`, and `UART2`.
- Default console documentation: `UART0` on **Pin 0** (`PTB16` RX) and
**Pin 1** (`PTB17` TX) at 115200 8N1 with 3.3V TTL wiring instructions.
5. **LED Status Indicators**:
- Documented LED status machine on pin `PTC5` under `CONFIG_ARCH_LEDS`
(idle statically ON, kernel panic flashing at 2 Hz).
6. **Flashing & Bootloader Walkthrough**:
- Installation and usage of `teensy_loader_cli` for both Teensy 3.1/3.2
(`--mcu=mk20dx256`) and Teensy 3.0 (`--mcu=mk20dx128`).
- Pushbutton bootloader invocation and automatic reboot into NuttX.
7. **Hardware Debugging (SWD / JTAG)**:
- Clarified why SWD debugging is not available out of the box due to
Mini54TAN control of Reset/SWD lines, with references for cutting debug traces
if using hardware probes (J-Link / CMSIS-DAP).
8. **Board Configurations**:
- Documented both supported configurations:
- `nsh`: Basic NuttShell prompt over UART0 serial console.
- `usbnsh`: NuttShell prompt over native USB CDC/ACM class driver
(`/dev/ttyACM0`) using Kinetis Full-Speed USB controller
(`CONFIG_KINETIS_USBOTG=y`).
Addresses #11077
Part of #15737
## Impact
- **Documentation only**: Zero functional impact on RTOS kernel, drivers, or
build scripts.
- Replaces raw monospaced `.. include:: README.txt :literal:` with
formatted, searchable Sphinx rST.
- Removes legacy `README.txt`.
## Testing
- Validated rST syntax, indentation, and table formatting with `docutils` (0
errors, 0 warnings).
- Verified Teensy 3.0 linker script filename (`mk20dx128vlh5.ld`) against
actual files in `boards/arm/kinetis/teensy-3.x/scripts/`.
- Verified defconfigs for `teensy-3.x:nsh` and `teensy-3.x:usbnsh`.
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