zstack 1.21 中为什么将P0_1 脚初始化为三态 ？ （CC2530+CC2591 PA ）

在PA 模式下， HGM_EN 为什么初始化为三态呢》？

#elif defined (HAL_BOARD_CC2530EB_REV13) || defined (HAL_PA_LNA) || \
      defined (HAL_PA_LNA_CC2590)

#define HAL_BOARD_INIT()                                         \
{                                                                \
  uint16 i;                                                      \
                                                                 \
  SLEEPCMD &= ~OSC_PD;                       /* turn on 16MHz RC and 32MHz XOSC */                \
  while (!(SLEEPSTA & XOSC_STB));            /* wait for 32MHz XOSC stable */                     \
  asm("NOP");                                /* chip bug workaround */                            \
  for (i=0; i<504; i++) asm("NOP");          /* Require 63us delay for all revs */                \
  CLKCONCMD = (CLKCONCMD_32MHZ | OSC_32KHZ); /* Select 32MHz XOSC and the source for 32K clock */ \
  while (CLKCONSTA != (CLKCONCMD_32MHZ | OSC_32KHZ)); /* Wait for the change to be effective */   \
  SLEEPCMD |= OSC_PD;                        /* turn off 16MHz RC */                              \
                                                                 \
  /* Turn on cache prefetch mode */                              \
  PREFETCH_ENABLE();                                             \
  /* LED_1 P10 EZMODE STATE LED_2 P12 NETWORKSTATE */            \
  LED1_DDR |= (LED1_BV | LED2_BV );                              \
                                                                 \
  /* Set PA/LNA HGM control P0_7 */                              \
  P0DIR |= BV(7);                                                \
                                                                 \
  /* configure tristates */                                      \
  P0INP |= PUSH2_BV;                                             \
                                                                 \
  /* setup RF frontend if necessary */                           \
  HAL_BOARD_RF_FRONTEND_SETUP();                                 \
}