diff options
| -rw-r--r-- | docs/library/pyb.DAC.rst | 21 | ||||
| -rw-r--r-- | ports/stm32/dac.c | 24 | ||||
| -rw-r--r-- | tests/pyb/dac.py | 4 |
3 files changed, 42 insertions, 7 deletions
diff --git a/docs/library/pyb.DAC.rst b/docs/library/pyb.DAC.rst index fd786b63b..3e236a3da 100644 --- a/docs/library/pyb.DAC.rst +++ b/docs/library/pyb.DAC.rst @@ -49,7 +49,7 @@ To output a continuous sine-wave at 12-bit resolution:: Constructors ------------ -.. class:: pyb.DAC(port, bits=8) +.. class:: pyb.DAC(port, bits=8, \*, buffering=None) Construct a new DAC object. @@ -60,12 +60,27 @@ Constructors The maximum value for the write and write_timed methods will be 2\*\*``bits``-1. + The *buffering* parameter selects the behaviour of the DAC op-amp output + buffer, whose purpose is to reduce the output impedance. It can be + ``None`` to select the default (buffering enabled for :meth:`DAC.noise`, + :meth:`DAC.triangle` and :meth:`DAC.write_timed`, and disabled for + :meth:`DAC.write`), ``False`` to disable buffering completely, or ``True`` + to enable output buffering. + + When buffering is enabled the DAC pin can drive loads down to 5KΩ. + Otherwise it has an output impedance of 15KΩ maximum: consequently + to achieve a 1% accuracy without buffering requires the applied load + to be less than 1.5MΩ. Using the buffer incurs a penalty in accuracy, + especially near the extremes of range. + Methods ------- -.. method:: DAC.init(bits=8) +.. method:: DAC.init(bits=8, \*, buffering=None) - Reinitialise the DAC. ``bits`` can be 8 or 12. + Reinitialise the DAC. *bits* can be 8 or 12. *buffering* can be + ``None``, ``False`` or ``True`; see above constructor for the meaning + of this parameter. .. method:: DAC.deinit() diff --git a/ports/stm32/dac.c b/ports/stm32/dac.c index bce30dbc7..04acfb8aa 100644 --- a/ports/stm32/dac.c +++ b/ports/stm32/dac.c @@ -143,11 +143,14 @@ typedef struct _pyb_dac_obj_t { uint16_t pin; // GPIO_PIN_4 or GPIO_PIN_5 uint8_t bits; // 8 or 12 uint8_t state; + uint8_t outbuf_single; + uint8_t outbuf_waveform; } pyb_dac_obj_t; STATIC mp_obj_t pyb_dac_init_helper(pyb_dac_obj_t *self, size_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) { static const mp_arg_t allowed_args[] = { { MP_QSTR_bits, MP_ARG_INT, {.u_int = 8} }, + { MP_QSTR_buffering, MP_ARG_KW_ONLY | MP_ARG_OBJ, {.u_rom_obj = MP_ROM_PTR(&mp_const_none_obj)} }, }; // parse args @@ -194,6 +197,19 @@ STATIC mp_obj_t pyb_dac_init_helper(pyb_dac_obj_t *self, size_t n_args, const mp mp_raise_ValueError("unsupported bits"); } + // set output buffer config + if (args[1].u_obj == mp_const_none) { + // due to legacy, default values differ for single and waveform outputs + self->outbuf_single = DAC_OUTPUTBUFFER_DISABLE; + self->outbuf_waveform = DAC_OUTPUTBUFFER_ENABLE; + } else if (mp_obj_is_true(args[1].u_obj)) { + self->outbuf_single = DAC_OUTPUTBUFFER_ENABLE; + self->outbuf_waveform = DAC_OUTPUTBUFFER_ENABLE; + } else { + self->outbuf_single = DAC_OUTPUTBUFFER_DISABLE; + self->outbuf_waveform = DAC_OUTPUTBUFFER_DISABLE; + } + // reset state of DAC self->state = DAC_STATE_RESET; @@ -289,7 +305,7 @@ STATIC mp_obj_t pyb_dac_noise(mp_obj_t self_in, mp_obj_t freq) { // configure DAC to trigger via TIM6 DAC_ChannelConfTypeDef config; config.DAC_Trigger = DAC_TRIGGER_T6_TRGO; - config.DAC_OutputBuffer = DAC_OUTPUTBUFFER_ENABLE; + config.DAC_OutputBuffer = self->outbuf_waveform; HAL_DAC_ConfigChannel(&DAC_Handle, &config, self->dac_channel); self->state = DAC_STATE_BUILTIN_WAVEFORM; } @@ -319,7 +335,7 @@ STATIC mp_obj_t pyb_dac_triangle(mp_obj_t self_in, mp_obj_t freq) { // configure DAC to trigger via TIM6 DAC_ChannelConfTypeDef config; config.DAC_Trigger = DAC_TRIGGER_T6_TRGO; - config.DAC_OutputBuffer = DAC_OUTPUTBUFFER_ENABLE; + config.DAC_OutputBuffer = self->outbuf_waveform; HAL_DAC_ConfigChannel(&DAC_Handle, &config, self->dac_channel); self->state = DAC_STATE_BUILTIN_WAVEFORM; } @@ -342,7 +358,7 @@ STATIC mp_obj_t pyb_dac_write(mp_obj_t self_in, mp_obj_t val) { if (self->state != DAC_STATE_WRITE_SINGLE) { DAC_ChannelConfTypeDef config; config.DAC_Trigger = DAC_TRIGGER_NONE; - config.DAC_OutputBuffer = DAC_OUTPUTBUFFER_DISABLE; + config.DAC_OutputBuffer = self->outbuf_single; HAL_DAC_ConfigChannel(&DAC_Handle, &config, self->dac_channel); self->state = DAC_STATE_WRITE_SINGLE; } @@ -454,7 +470,7 @@ mp_obj_t pyb_dac_write_timed(size_t n_args, const mp_obj_t *pos_args, mp_map_t * if (self->state != DAC_STATE_DMA_WAVEFORM + dac_trigger) { DAC_ChannelConfTypeDef config; config.DAC_Trigger = dac_trigger; - config.DAC_OutputBuffer = DAC_OUTPUTBUFFER_ENABLE; + config.DAC_OutputBuffer = self->outbuf_waveform; HAL_DAC_ConfigChannel(&DAC_Handle, &config, self->dac_channel); self->state = DAC_STATE_DMA_WAVEFORM + dac_trigger; } diff --git a/tests/pyb/dac.py b/tests/pyb/dac.py index 6f03bbc64..ca68ec709 100644 --- a/tests/pyb/dac.py +++ b/tests/pyb/dac.py @@ -12,3 +12,7 @@ dac.write(0) dac.write_timed(bytearray(10), 100, mode=pyb.DAC.NORMAL) pyb.delay(20) dac.write(0) + +# test buffering arg +dac = pyb.DAC(1, buffering=True) +dac.write(0) |