#include <msp430g2553.h>


#define DATA_REGISTER r13
#define CHIP_ID_REGISTER r12

#define PORT_REG P1OUT
#define PORT_SID_BIT BIT0
#define PORT_SCK_BIT BIT1
#define PORT_LATI0_BIT BIT2
#define PORT_LATI1_BIT BIT3

  .altmacro

  .macro set_data_bit
  bic         #PORT_SID_BIT, &PORT_REG
  .endm
  .macro clear_data_bit
  bis         #PORT_SID_BIT, &PORT_REG
  .endm
  .macro clock_cycle
  bic         #PORT_SCK_BIT, &PORT_REG
  bis         #PORT_SCK_BIT, &PORT_REG
  .endm
  .macro lati_cycle chip
  bic         #\chip\(), &PORT_REG
  bis         #\chip\(), &PORT_REG
  .endm

  .macro data_cycle id
genShifter_\id\():
  rra.w       DATA_REGISTER
  jnc         genShifter_false_\id\()
  set_data_bit
  jmp         genShifter_clock_\id\()
genShifter_false_\id\():
  clear_data_bit
genShifter_clock_\id\():
  clock_cycle
  .endm
 
  .section ".text","ax",@progbits
  .global genShifter
genShifter:
  // arguments
  //   R12 aka CHIP_ID_REGISTER: chip id, 0 or 1
  //   R13 aka DATA_REGISTER: frequency code, full 16 bit

  .set counter, 0
  .rept 16
    data_cycle %counter
    .set counter, counter + 1
  .endr

  tst.w       CHIP_ID_REGISTER
  jnz         genShifter_chip_1
  lati_cycle PORT_LATI0_BIT
genShifter_chip_1:
  lati_cycle PORT_LATI1_BIT

  ret