adjust UART settings and update readme

Author: miyazakh

IDE/Renesas/e2studio/RA6M4/Readme.md

@@ -158,12 +158,29 @@ Key BSP settings configured above (`wolfBoot/ra_cfg/fsp_cfg/bsp/bsp_cfg.h`):
 
 wolfBoot initialises the FACI HP directly; **no FSP flash stack (`g_flash0`) is required**.
 
-To enable debug output over UART (SCI7, P613=TXD7, J23 connector), edit `wolfBoot/user_settings.h`:
+#### 2-3) Enable Debug UART Output (optional)
+
+Defining `DEBUG_UART` enables `wolfBoot_printf()` output over SCI7.
+Edit `wolfBoot/user_settings.h` and uncomment both lines:
+
 ```c
 #define DEBUG_UART
 #define PRINTF_ENABLED
 ```
 
+**UART channel and pin assignment (EK-RA6M4):**
+
+| Signal | Port pin | Board connector | Note |
+|:--|:--|:--|:--|
+| TXD7 | P613 | J23 Pin2 (silk: TX►0) | Connect to RXD of USB-UART adapter |
+| RXD7 | P614 | J23 Pin1 (silk: RX◄0) | Connect to TXD of USB-UART adapter |
+| GND  | —    | J24 Pin7 | Common ground |
+
+**Terminal settings:** 115200 bps, 8N1, no flow control.
+
+> **Note**: SCI7 on RA6M4 uses **PCLKA (100 MHz)**, not PCLKB (50 MHz).
+> The BRR value in `hal/renesas-ra.h` is calculated accordingly (`RA_PCLKA_SCI = 100000000U`).
+
 #### 2-2) Modify wolfBoot hal_entry.c
 
 `wolfBoot/src/hal_entry.c` is **not stored in the repository** (Renesas copyright, FSP-generated).

IDE/Renesas/e2studio/RA6M4/wolfBoot/user_settings.h

@@ -317,5 +317,4 @@
 
 #define NVM_FLASH_WRITEONCE
 /*#define DEBUG_UART*/
-/*#define PRINTF_ENABLED*/
 #endif /* !H_USER_SETTINGS_ */

hal/renesas-ra.h

@@ -125,17 +125,20 @@
 #define PFS_PMR         (1u << 16)
 #define PFS_PDR         (1u << 2)
 #define PFS_PODR        (1u << 0)
-#define PFS_PSEL_SCI7   (0x05u << 24)  /* PSEL=0x05: SCI1/3/5/7/9 odd channels */
+#define PFS_PSEL_SCI7   (0x05u << 24) /* PSEL=0x05: SCI1/3/5/7/9 odd channels */
 #define R_PMISC_PWPR    REG8(0x40080D03UL)
 #define PWPR_PFSWE      (1u << 6)
 #define PWPR_B0WI       (1u << 7)
 #ifndef DEBUG_BAUD_RATE
  #define DEBUG_BAUD_RATE 115200U
 #endif
-#ifndef RA_PCLKB
- #define RA_PCLKB        50000000U
+/* SCI7 on RA6M4 is clocked by PCLKA (not PCLKB).
+ * Default EK-RA6M4 FSP config: PLL=200MHz, PCLKA Div/2 = 100MHz. */
+#ifndef RA_PCLKA_SCI
+ #define RA_PCLKA_SCI    100000000U  /* PCLKA = 100MHz */
 #endif
-#define SCI_BRR_VAL    (RA_PCLKB / (8U * DEBUG_BAUD_RATE) - 1U)
+/* BRR: BGDM=1, ABCS=1 -> divisor=8. 100MHz/(8*115200)-1 = 107 -> 115741bps */
+#define SCI_BRR_VAL    (RA_PCLKA_SCI / (8U * DEBUG_BAUD_RATE) - 1U)
 /* --- Flash error codes (used by flash_check_error) --- */
 typedef enum {
     FLASH_OK        = 0,