diff --git a/include/rtl8710bx.h b/include/rtl8710bx.h
index 6bb2215..4935328 100644
--- a/include/rtl8710bx.h
+++ b/include/rtl8710bx.h
@@ -904,22 +904,13 @@ typedef struct {
 #define PAD_DRV_STRENGTH_6 (0x00000006 << 9)
 #define PAD_DRV_STRENGTH_7 (0x00000007 << 9)
 
-static inline void PINMUX_Config_BL(uint32_t pin, uint32_t func) {
+static inline void PINMUX_Config(uint32_t pin, uint32_t func) {
   volatile uint32_t *reg = &PERI_ON->GPIO_PINMUX_CTRL[pin >> 1];
   uint32_t shift = (pin & 1) << 4;
   uint32_t mask = 0xFFFF << shift;
   *reg = (*reg & ~mask) | (func << shift);
 }
 
-static inline void PINMUX_Config(uint32_t pin, uint32_t func) {
-  volatile uint32_t *reg = &PERI_ON->GPIO_PINMUX_CTRL[pin >> 1];
-  if (pin & 1) {
-    *reg = (*reg & 0x0000FFFF) | (func << 16);
-  } else {
-    *reg = (*reg & 0xFFFF0000) | func;
-  }
-}
-
 static inline void PINMUX_ConfigPadPull(uint8_t pin, uint8_t pull_type) {
   uint32_t reg_index = pin >> 1;
   uint32_t bit_pos = (pin & 1) << 4;
diff --git a/linker.ld b/linker.ld
index d7d2ed0..a2a1462 100644
--- a/linker.ld
+++ b/linker.ld
@@ -8,7 +8,7 @@ MEMORY
 
 SECTIONS
 {
-    _stack_top = ORIGIN(RAM) + LENGTH(RAM) - (4 * 1024) - 4;
+    _stack_top = ORIGIN(RAM) + LENGTH(RAM) - 0x4000;
 
     .rom_header : {
         LONG(0x96969999) LONG(0xFC66CC3F)
diff --git a/src/boot.s b/src/boot.s
index 255eefc..fa1d91c 100644
--- a/src/boot.s
+++ b/src/boot.s
@@ -4,24 +4,23 @@
 .section .text
 .thumb_func
 _startup:
-    // zero .bss section
+    /* zero .bss section */
     ldr r0, =_bss_start
     ldr r1, =_bss_end
     movs r2, #0
 1:  cmp r0, r1
-    beq 2f
-    str r2, [r0], #4
-    b 1b
+    itt lt
+    strlt r2, [r0], #4
+    blt 1b
 2:
     bl main
 1:  b 1b
 
 .section .text
 .global _init
+/* cold boot from ROM */
 _init:
-    ldr r0, =0x1003E000
-    mov sp, r0
-
+    ldr sp, =_stack_top
     ldr r0, =_vector_table
     ldr r1, =0xE000ED08
     str r0, [r1]
diff --git a/src/main.c b/src/main.c
index bc94346..a37bb4f 100644
--- a/src/main.c
+++ b/src/main.c
@@ -26,9 +26,6 @@ int main(void) {
 
   PERI_ON->SOC_PERI_FUNC1_EN |= BIT_PERI_GPIO_EN;
   PERI_ON->PESOC_CLK_CTRL |= APBPeriph_GPIO_CLOCK;
-  // branchless
-  PINMUX_Config_BL(_PA_0, PINMUX_FN_GPIO);
-  // 
   PINMUX_Config(_PA_0, PINMUX_FN_GPIO);
   PINMUX_ConfigPadPull(_PA_0, GPIO_PuPd_DOWN);
   GPIOA->DDR |= (1 << 0);