kinetis_k: non-blocking board_uart_read (RX FIFO) + SIM unique id

- board_uart_read was a stub returning 0, so host examples that bridge the
  UART console to a CDC device (echo test) received nothing. Implement it via
  an RDRF-interrupt-fed tu_fifo, matching the stm32 family (non-blocking, no
  RX overrun). board_uart_write is already non-blocking.
- implement board_get_unique_id() from the SIM 128-bit UID registers so
  frdm_k64f/teensy_35 report a real USB serial instead of the fixed default.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>
Claude-Session: https://claude.ai/code/session_01ExGPLP5eU43LR7o6yYLpNi

1 files changed, 35 insertions, 6 deletions

diff --git a/hw/bsp/kinetis_k/family.c b/hw/bsp/kinetis_k/family.c
index a5af83931..238123f30 100644
--- a/hw/bsp/kinetis_k/family.c
+++ b/hw/bsp/kinetis_k/family.c
@@ -35,10 +35,25 @@
 #include "fsl_clock.h"
 #include "fsl_uart.h"
 #include "fsl_sysmpu.h"
+#include "common/tusb_fifo.h"
 
 #include "board/clock_config.h"
 #include "board/pin_mux.h"
 
+#ifdef UART_DEV
+// RX ring buffer filled by the RDRF interrupt so board_uart_read() is non-blocking
+// and does not drop bytes to UART overrun (see stm32 family for reference).
+static uint8_t   uart_rx_ff_buf[32];
+static tu_fifo_t uart_rx_ff;
+
+void UART0_RX_TX_IRQHandler(void) {
+  if (UART_DEV->S1 & UART_S1_RDRF_MASK) {
+    uint8_t byte = UART_DEV->D; // reading S1 then D clears RDRF (and any overrun)
+    tu_fifo_write(&uart_rx_ff, &byte);
+  }
+}
+#endif
+
 //--------------------------------------------------------------------+
 // Forward USB interrupt events to TinyUSB IRQ Handler
 //--------------------------------------------------------------------+
@@ -89,6 +104,9 @@ void board_init(void) {
       .enableRx = true
   };
   UART_Init(UART_DEV, &uart_config, UART_CLOCK);
+  tu_fifo_config(&uart_rx_ff, uart_rx_ff_buf, sizeof(uart_rx_ff_buf), false);
+  UART_DEV->C2 |= UART_C2_RIE_MASK; // enable RX data register full interrupt
+  NVIC_EnableIRQ(UART0_RX_TX_IRQn);
 #endif
 
   // USB
@@ -112,14 +130,11 @@ uint32_t board_button_read(void) {
 }
 
 int board_uart_read(uint8_t *buf, int len) {
-  (void) buf;
-  (void) len;
 #ifdef UART_DEV
-  // Read blocking will block until there is data
-//  UART_ReadBlocking(UART_DEV, buf, len);
-//  return len;
-  return 0;
+  return (int) tu_fifo_read_n(&uart_rx_ff, buf, (uint16_t) len);
 #else
+  (void) buf;
+  (void) len;
   return 0;
 #endif
 }
@@ -144,6 +159,20 @@ int board_uart_write(void const *buf, int len) {
 #endif
 }
 
+size_t board_get_unique_id(uint8_t id[], size_t max_len) {
+  (void) max_len;
+  // Kinetis 128-bit Unique Identification Register (SIM->UIDH/UIDMH/UIDML/UIDL)
+  uint32_t* id32 = (uint32_t*) (uintptr_t) id;
+  uint8_t const len = 16;
+
+  id32[0] = SIM->UIDH;
+  id32[1] = SIM->UIDMH;
+  id32[2] = SIM->UIDML;
+  id32[3] = SIM->UIDL;
+
+  return len;
+}
+
 #if CFG_TUSB_OS == OPT_OS_NONE
 volatile uint32_t system_ticks = 0;