arch/mips: Add basic support for MIPS Creator CI20 board

[ldube]

Summary

This commit introduces a rudimentary architecture and board port for the MIPS Creator CI20, featuring the dual core Ingenic JZ4780 SoC (MIPS32).

Included in this initial implementation:

• Basic architectural initialization and startup code for the JZ4780 Core 0.
• Minimal configuration required to execute from RAM.
• Early UART/serial console support for basic debugging and NSH output.
• Minimal board-specific configuration for the CI20 target.
• Console output is routed via UART0 on the expansion header.

This establishes basic support for running NuttX on the MIPS CI20. Further peripherals, optimization, and extended documentation are left for future iterations or community contributions.

Build and Runtime Deployment Info:

The baseline can be configured, compiled using the MIPS MTI toolchain, and loaded via U-Boot using the following commands (replace <tftp_dir> with your local TFTP root directory).

./tools/configure.sh -l ci20/nsh
make CROSSDEV=mips-mti-elf-
mkimage -A mips -O linux -T kernel -C none -a 0x80000180 -e 0x800004ac
-n "nx" -d nuttx.bin <tftp_dir>/nuttx.umg

Note: U-Boot must be properly configured for networking (e.g., valid ipaddr, serverip, and ethaddr environment variables) to fetch the image over TFTP.

Run this from U-Boot prompt:
tftp nuttx.umg && bootm $fileaddr

Testing

The port has been verified on target hardware. The system successfully boots from RAM into the NuttShell (NSH) via the serial console, with the scheduler running normally:

NuttShell (NSH) NuttX-13.0.0
nsh> ps
TID PID PPID PRI POLICY TYPE NPX STATE EVENT SIGMASK STACK COMMAND
0 0 0 0 FIFO Kthread - Ready 0000000000000000 0002024
1 0 0 50 RR Kthread - Waiting Semaphore 0000000000000000 0001976 0x800589b8 0x80058a08
3 3 0 100 RR Task - Running 0000000000000000 0002004
nsh>

[github-actions]

MemBrowse Memory Report

No memory changes detected for:

• arduino-mega2560
• esp32-devkitc
• hifive1-revb
• mirtoo
• qemu-armv8a
• qemu-intel64
• rx65n-rsk2mb
• s698pm-dkit
• stm32-nucleo-f103rb

[xiaoxiang781216]

@ldube please create a new patch in this pr fix the following compiler error:

====================================================================================
Configuration/Tool: ci20/nsh,CONFIG_MIPS32_TOOLCHAIN_PINGUINOL
2026-07-13 06:56:52
------------------------------------------------------------------------------------
  Cleaning...
  Configuring...
  Disabling CONFIG_MIPS32_TOOLCHAIN_GNU_ELF
  Enabling CONFIG_MIPS32_TOOLCHAIN_PINGUINOL
  Building NuttX...
serial/uart_16550.c: In function 'u16550_sendbuf':
Error: serial/uart_16550.c:1586:3: error: 'for' loop initial declarations are only allowed in C99 or C11 mode
   for (size_t i = 0; i < size; i++)
   ^
serial/uart_16550.c:1586:3: note: use option -std=c99, -std=gnu99, -std=c11 or -std=gnu11 to compile your code
make[1]: *** [Makefile:108: uart_16550.o] Error 1
make[1]: Target 'libdrivers.a' not remade because of errors.
make: *** [tools/LibTargets.mk:107: drivers/libdrivers.a] Error 2
mm_gran/mm_grantable.c: In function 'gran_search':
Error: mm_gran/mm_grantable.c:270:3: error: 'for' loop initial declarations are only allowed in C99 or C11 mode