8000 Tweaks to PIO clkdiv-setting code by lurch · Pull Request #254 · raspberrypi/pico-sdk · GitHub
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Tweaks to PIO clkdiv-setting code #254

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Mar 24, 2021
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Tweaks to PIO clkdiv-setting code #254

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82 changes: 45 additions & 37 deletions src/rp2_common/hardware_pio/include/hardware/pio.h
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Original file line number Diff line number Diff line change
Expand Up @@ -196,29 +196,6 @@ static inline void sm_config_set_sideset(pio_sm_config *c, uint bit_count, bool
(bool_to_bit(pindirs) << PIO_SM0_EXECCTRL_SIDE_PINDIR_LSB);
}

/*! \brief Set the state machine clock divider (from a floating point value) in a state machine configuration
* \ingroup sm_config
*
* The clock divider slows the state machine's execution by masking the
* system clock on some cycles, in a repeating pattern, so that the state
* machine does not advance. Effectively this produces a slower clock for the
* state machine to run from, which can be used to generate e.g. a particular
* UART baud rate. See the datasheet for further detail.
*
* \param c Pointer to the configuration structure to modify
* \param div The fractional divisor to be set. 1 for full speed. An integer clock divisor of n
* will cause the state machine to run 1 cycle in every n.
* Note that for small n, the jitter introduced by a fractional divider (e.g. 2.5) may be unacceptable
* although it will depend on the use case.
*/
static inline void sm_config_set_clkdiv(pio_sm_config *c, float div) {
uint div_int = (uint)div;
uint div_frac = (uint)((div - (float)div_int) * (1u << 8u));
c->clkdiv =
(div_frac << PIO_SM0_CLKDIV_FRAC_LSB) |
(div_int << PIO_SM0_CLKDIV_INT_LSB);
}

/*! \brief Set the state machine clock divider (from integer and fractional parts - 16:8) in a state machine configuration
* \ingroup sm_config
*
Expand All @@ -238,6 +215,38 @@ static inline void sm_config_set_clkdiv_int_frac(pio_sm_config *c, uint16_t div_
(((uint)div_int) << PIO_SM0_CLKDIV_INT_LSB);
}

static inline void pio_calculate_clkdiv_from_float(float div, uint16_t *div_int, uint8_t *div_frac) {
valid_params_if(PIO, div >= 1 && div <= 65536);
*div_int = (uint16_t)div;
if (*div_int == 0) {
*div_frac = 0;
} else {
*div_frac = (uint8_t)((div - (float)*div_int) * (1u << 8u));
}
}

/*! \brief Set the state machine clock divider (from a floating point value) in a state machine configuration
* \ingroup sm_config
*
* The clock divider slows the state machine's execution by masking the
* system clock on some cycles, in a repeating pattern, so that the state
* machine does not advance. Effectively this produces a slower clock for the
* state machine to run from, which can be used to generate e.g. a particular
* UART baud rate. See the datasheet for further detail.
*
* \param c Pointer to the configuration structure to modify
* \param div The fractional divisor to be set. 1 for full speed. An integer clock divisor of n
* will cause the state machine to run 1 cycle in every n.
* Note that for small n, the jitter introduced by a fractional divider (e.g. 2.5) may be unacceptable
* although it will depend on the use case.
*/
static inline void sm_config_set_clkdiv(pio_sm_config *c, float div) {
uint16_t div_int;
uint8_t div_frac;
pio_calculate_clkdiv_from_float(div, &div_int, &div_frac);
sm_config_set_clkdiv_int_frac(c, div_int, div_frac);
}

/*! \brief Set the wrap addresses in a state machine configuration
* \ingroup sm_config
*
Expand Down Expand Up @@ -978,37 +987,36 @@ static inline uint32_t pio_sm_get_blocking(PIO pio, uint sm) {
*/
void pio_sm_drain_tx_fifo(PIO pio, uint sm);

/*! \brief set the current clock divider for a state machine
/*! \brief set the current clock divider for a state machine using a 16:8 fraction
* \ingroup hardware_pio
*
* \param pio The PIO instance; either \ref pio0 or \ref pio1
* \param sm State machine index (0..3)
* \param div the floating point clock divider
* \param div_int the integer part of the clock divider
* \param div_frac the fractional part of the clock divider in 1/256s
*/
static inline void pio_sm_set_clkdiv(PIO pio, uint sm, float div) {
static inline void pio_sm_set_clkdiv_int_frac(PIO pio, uint sm, uint16_t div_int, uint8_t div_frac) {
check_pio_param(pio);
check_sm_param(sm);
uint div_int = (uint16_t) div;
uint div_frac = (uint8_t) ((div - (float)div_int) * (1u << 8u));
pio->sm[sm].clkdiv =
(div_frac << PIO_SM0_CLKDIV_FRAC_LSB) |
(div_int << PIO_SM0_CLKDIV_INT_LSB);
(((uint)div_frac) << PIO_SM0_CLKDIV_FRAC_LSB) |
(((uint)div_int) << PIO_SM0_CLKDIV_INT_LSB);
}

/*! \brief set the current clock divider for a state machine using a 16:8 fraction
/*! \brief set the current clock divider for a state machine
* \ingroup hardware_pio
*
* \param pio The PIO instance; either \ref pio0 or \ref pio1
* \param sm State machine index (0..3)
* \param div_int the integer part of the clock divider
* \param div_frac the fractional part of the clock divider in 1/256s
* \param div the floating point clock divider
*/
static inline void pio_sm_set_clkdiv_int_frac(PIO pio, uint sm, uint16_t div_int, uint8_t div_frac) {
static inline void pio_sm_set_clkdiv(PIO pio, uint sm, float div) {
check_pio_param(pio);
check_sm_param(sm);
pio->sm[sm].clkdiv =
(((uint)div_frac) << PIO_SM0_CLKDIV_FRAC_LSB) |
(((uint)div_int) << PIO_SM0_CLKDIV_INT_LSB);
uint16_t div_int;
uint8_t div_frac;
pio_calculate_clkdiv_from_float(div, &div_int, &div_frac);
pio_sm_set_clkdiv_int_frac(pio, sm, div_int, div_frac);
}

/*! \brief Clear a state machine's TX and RX FIFOs
Expand Down
0