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;

; Copyright 2012, Sinclair R.F., Inc.

;

; Major I2C functions:

;   i2c_send_start      ( - )

;   i2c_send_byte       ( u - f )

;   i2c_read_byte       ( - u )

;   i2c_send_stop       ( - )

;

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; Compute how many iterations in the quarter-clock-cycle function are required.

;   ceil(100 MHz / 400 kHz / 4) ==> 63 clock cycles per I2C SCL quarter cycle

;   The function consumes:

;     3 clock cycles to call the function

;     3 clock cycles for the "outport(O_SCL)"

;     1 clock cycle to initialize the loop count

;     2 clock cycles to return

;     9 TOTAL

;   Add 2 to ensure rounding up when evaluting the integer fraction.

;   The loop is 3 clock cycles per iteration

.constant C_I2C_QUARTER_CYCLE ${(63-9+2)/3}

; ( - )

.function i2c_send_start

  .call(i2c_quarter_cycle,1)

  .call(i2c_quarter_cycle,0)

.return

; Set a start without the preceding stop.

; ( - )

.function i2c_send_restart

  .call(i2c_quarter_cycle,0)

  .call(i2c_quarter_cycle,1)

  .call(i2c_quarter_cycle,0)

.return

; Send the byte and indicate false if the acknowledge bit was received.

; ( u - f )

.function i2c_send_byte

  ; send the byte, msb first

  ; ( u - )

  ${8-1} :outer

    ; send the next bit

    swap <<msb swap

    .call(i2c_clock_cycle,over) drop

  .jumpc(outer,1-) drop drop

  ; get the acknowledge bit at the middle of the high portion of SCL

  ; ( - f )

  .call(i2c_clock_cycle,1)

.return

; Read the next byte from the device.

; ( - u )

.function i2c_read_byte

    swap <<0 .call(i2c_clock_cycle,1) or swap

  .jumpc(loop,1-) drop

  ; send the acknowledgment bit

  .call(i2c_clock_cycle,0)

.return(drop)

; Send a stop by bringing SDA high while SCL is high.

; ( - )

.function i2c_send_stop

  .call(i2c_quarter_cycle,1)

  1 .outport(O_SDA) .call(i2c_quarter_cycle,1)

.return

; Send the clock as a "0110" pattern and sample SDA in the middle of the high

; portion.

; ( u_sda_out - u_sda_in )

.function i2c_clock_cycle

  .outport(O_SDA)

  .call(i2c_quarter_cycle,0)

  .call(i2c_quarter_cycle,1)

  .inport(I_SDA)

  .call(i2c_quarter_cycle,1)

  .call(i2c_quarter_cycle,0)

.return

; Output the I2C SCL value and then wait for a quarter of the I2C clock cycle.

; ( u_scl - )

.function i2c_quarter_cycle

  .outport(O_SCL)

  ${C_I2C_QUARTER_CYCLE-1} :loop .jumpc(loop,1-)

.return(drop)