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  1.  
  2. import time
  3. import microcontroller
  4. import digitalio
  6. DAP_TRANSFER_OK = 1 << 0
  7. DAP_TRANSFER_RnW = 1 << 1
  8. DAP_TRANSFER_WAIT = 1 << 1
  9. DAP_TRANSFER_FAULT = 1 << 2
  10. DAP_TRANSFER_ERROR = 1 << 3
  12. class SWD:
  13. def __init__(self, swdio, swclk):
  14. self.swdio = swdio
  15. self.swclk = swclk
  16. self.swclk = digitalio.DigitalInOut(swclk)
  17. self.swclk.switch_to_output()
  18. self.swclk.value = 1
  19. self.swdio = digitalio.DigitalInOut(swdio)
  20. self.swdio.switch_to_output()
  21. self.swdio.value = 1
  22. self.turnaround = 1
  23. self.idle_cycles = 0
  24. self.data_phase = 0
  26. def sw_clk_cycle(self):
  27. self.swclk.value = 0
  28. microcontroller.delay_us(1)
  29. self.swclk.value = 1
  30. microcontroller.delay_us(1)
  32. def sw_write_bit(self, bit):
  33. self.swdio.switch_to_output()
  34. self.swdio.value = bit
  35. self.swclk.value = 0
  36. microcontroller.delay_us(1)
  37. self.swclk.value = 1
  38. microcontroller.delay_us(1)
  40. def sw_read_bit(self):
  41. self.swclk.value = 0
  42. microcontroller.delay_us(1)
  43. self.swdio.switch_to_input()
  44. bit = self.swdio.value
  45. self.swclk.value = 1
  46. microcontroller.delay_us(1)
  47. return bit
  49. def swd_transfer(self, request, data=None):
  50. # Packet Request
  51. parity = 0
  52. self.sw_write_bit(1)
  53. bit = request >> 0
  54. self.sw_write_bit(bit)
  55. parity += bit
  56. bit = request >> 1
  57. self.sw_write_bit(bit)
  58. parity += bit
  59. bit = request >> 2
  60. self.sw_write_bit(bit)
  61. parity += bit
  62. bit = request >> 3
  63. self.sw_write_bit(bit)
  64. parity += bit
  65. self.sw_write_bit(parity)
  66. self.sw_write_bit(0)
  67. self.sw_write_bit(1)
  69. # Turnaround
  70. self.swdio.switch_to_input()
  71. for n in range(self.turnaround, 0, -1):
  72. self.sw_clk_cycle()
  74. # Ack
  75. bit = self.sw_read_bit()
  76. ack = bit << 0
  77. bit = self.sw_read_bit()
  78. ack |= bit << 1
  79. bit = self.sw_read_bit()
  80. ack |= bit << 2
  82. if (ack == DAP_TRANSFER_OK):
  83. # Data Transfer
  84. if (request & DAP_TRANSFER_RnW):
  85. # Read data
  86. val = 0
  87. parity = 0
  88. for n in range (32, 0, -1):
  89. bit = self.sw_read_bit()
  90. parity += bit
  91. val >>= 1
  92. val |= bit << 31
  93. bit = self.sw_read_bit()
  94. if ((parity ^ bit) & 1):
  95. ack = DAP_TRANSFER_ERROR
  96. data = val
  97. # Turnaround
  98. for n in range(n, 0, -1):
  99. self.sw_clk_cycle()
  100. self.swdio.switch_to_output()
  101. else:
  102. # Turnaround
  103. for n in range(n, 0, -1):
  104. self.sw_clk_cycle()
  105. self.swdio.switch_to_output()
  106. # Write data
  107. val = data
  108. parity = 0
  109. for n in range (32, 0, -1):
  110. self.sw_write_bit(val)
  111. parity += val
  112. val >>= 1
  113. self.sw_write_bit(parity)
  114. # Idle cycles
  115. n = self.idle_cycles
  116. if (n):
  117. self.swdio.value = 0
  118. for _ in range(n, 0, -1):
  119. self.sw_clk_cycle()
  120. self.swdio.value = 1
  121. return (ack, data)
  123. if (ack == DAP_TRANSFER_WAIT or ack == DAP_TRANSFER_FAULT):
  124. # WAIT or FAULT response
  125. if (self.data_phase and ((request & DAP_TRANSFER_RnW) != 0)):
  126. for n in range (33, 0, -1):
  127. self.sw_clk_cycle()
  128. # Turnaround
  129. for n in range(n, 0, -1):
  130. self.sw_clk_cycle()
  131. self.swdio.switch_to_output()
  133. if (self.data_phase and ((request & DAP_TRANSFER_RnW) == 0)):
  134. self.swdio.value = 0
  135. for n in range (33, 0, -1):
  136. self.sw_clk_cycle()
  137. self.swdio.value = 1
  138. return (ack, data)
  140. # Protocol error
  141. for n in range(self.turnaround + 33, 0, -1):
  142. self.sw_clk_cycle();
  143. self.swdio.switch_to_output()
  144. self.swdio.value = 1
  145. return (ack, data)
  147. if __name__ == "__main__":
  148. import board
  149. swd = SWD(board.D12, board.D11)
  150. while True:
  151. print("displaying debug port register 0")
  152. # Read debug port register
  153. SWD_REG_DP = 0
  154. SWD_REG_R = 1 << 1
  155. SWD_REG_ADR = 0 & 0x0c
  156. tmp_in = SWD_REG_DP | SWD_REG_R | SWD_REG_ADR
  157. response = swd.swd_transfer(tmp_in)
  158. ack = response[0]
  159. data = response[1]
  160. if data is not None:
  161. print("0x%x" %data)
  162. else:
  163. print(data)
  164. time.sleep(1)
  165.  
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