dcgong2917 opened a new pull request, #20334:
URL: https://github.com/apache/nuttx/pull/20334
## Summary
Expose the RTL8730E (AmebaSmart, dual-core Cortex-A32) general-purpose
UARTs through the shared Ameba serial driver, plus a chip-side SMP
stability fix that multi-port UART traffic surfaced.
Three commits:
1. **boards/arm/rtl8730e: fix SMP cache-line false sharing on Cortex-A32**
Under sustained dual-core critical-section traffic (e.g. several UART
ISRs) the two A32 cores live-lock. The generic `g_cpu_irqlock`
(LDREX/STREX spinlock) and `g_cpu_irqset` (plain non-atomic bitmap)
sit in the same 64-byte cache line; the A32 exclusive monitor reserves
a full cache line, so one core's store to `g_cpu_irqset` clears the
other core's LDREX reservation on `g_cpu_irqlock`. Separated onto their
own cache lines in the board link script — the generic scheduler source
is left untouched (relies on `-fdata-sections`).
2. **arch/arm/rtl8730e: add UART character driver support**
Chip glue (`ameba_uart_chip.h`: register bases, GIC IRQs SPI 50/51/52,
APB clocks, pin-mux), build wiring, and a board port table registering
UART0-2 as `/dev/ttyS1-3` at 115200 8N1 (LOG-UART keeps the console and
`/dev/ttyS0`; UART3 reserved for Bluetooth). Gated by
`CONFIG_AMEBA_UART`
(default off). Also fixes an RX-timeout interrupt storm in the shared
driver: the latched RX-timeout status (LSR bit9) isn't cleared by
draining the FIFO, so on the level-triggered GIC the ISR must write
TOICF, matching the vendor SDK. Harmless on the NVIC-based M33 parts.
3. **Documentation/rtl8730e: document the general-purpose UART ports**
## Impact
New optional feature for RTL8730E only; `CONFIG_AMEBA_UART` defaults off,
so existing configs are unaffected. The shared `ameba_uart.c` change (TOICF
clear) is a no-op on M33 Ameba parts.
## Testing
- `checkpatch` / `cmake-format`: clean on all 3 commits.
- Builds: `rtl8730e_evb:uart`, `rtl8730e_evb:nsh` (no AMEBA_UART), and
`rtl8721f_evb:nsh` (M33 regression for the shared driver) all pass;
`uart` defconfig matches `savedefconfig`.
- Hardware (RTL8730E EVB): `/dev/ttyS1` (UART0 PA3↔PA2) and `/dev/ttyS2`
(UART1 PA5↔PA4) loopback each report `Total bytes received = 26` with no
live-lock; NSH stays responsive across repeated runs.
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