2022-01-03 08:11:51

by Paulo Miguel Almeida

Subject: [PATCH] staging: pi433: fix frequency deviation check

rf69 datasheet states that frequency deviation must exceed 600 Hz but
also that frequency deviation + (bitrate / 2) should be less than equal
to 500 kHz to ensure proper modulation.

This patch validates that both conditions are met so RF intersymbol
interference is "avoided" where possible.

Signed-off-by: Paulo Miguel Almeida <[email protected]>
---
drivers/staging/pi433/rf69.c | 20 ++++++++++++++++----
1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/drivers/staging/pi433/rf69.c b/drivers/staging/pi433/rf69.c
index e62e61ef4d27..cc22915fd489 100644
--- a/drivers/staging/pi433/rf69.c
+++ b/drivers/staging/pi433/rf69.c
@@ -255,17 +255,29 @@ int rf69_set_deviation(struct spi_device *spi, u32 deviation)
int retval;
u64 f_reg;
u64 f_step;
+ u32 bit_rate_reg;
+ u32 bit_rate;
u8 msb;
u8 lsb;
u64 factor = 1000000; // to improve precision of calculation

- // TODO: Dependency to bitrate
- if (deviation < 600 || deviation > 500000) {
- dev_dbg(&spi->dev, "set_deviation: illegal input param");
+ // calculate bit rate
+ bit_rate_reg = rf69_read_reg(spi, REG_BITRATE_MSB) << 8;
+ bit_rate_reg |= rf69_read_reg(spi, REG_BITRATE_LSB);
+ bit_rate = F_OSC / bit_rate_reg;
+
+ /*
+ * frequency deviation must exceed 600 Hz and but not exceed
+ * 500kHz when taking bitrate dependency into consideration
+ * to ensure proper modulation
+ */
+ if (deviation < 600 || (deviation + (bit_rate / 2)) > 500000) {
+ dev_dbg(&spi->dev,
+ "set_deviation: illegal input param: %u", deviation);
return -EINVAL;
}

- // calculat f step
+ // calculate f step
f_step = F_OSC * factor;
do_div(f_step, 524288); // 524288 = 2^19

--
2.25.4

2022-01-03 10:00:10

by Fabio Aiuto

Subject: Re: [PATCH] staging: pi433: fix frequency deviation check

Hello Paulo,

thanks for your patch.

On Mon, Jan 03, 2022 at 09:11:35PM +1300, Paulo Miguel Almeida wrote:
> rf69 datasheet states that frequency deviation must exceed 600 Hz but
> also that frequency deviation + (bitrate / 2) should be less than equal
> to 500 kHz to ensure proper modulation.
>
> This patch validates that both conditions are met so RF intersymbol
> interference is "avoided" where possible.
>
> Signed-off-by: Paulo Miguel Almeida <[email protected]>
> ---
> drivers/staging/pi433/rf69.c | 20 ++++++++++++++++----
> 1 file changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/staging/pi433/rf69.c b/drivers/staging/pi433/rf69.c
> index e62e61ef4d27..cc22915fd489 100644
> --- a/drivers/staging/pi433/rf69.c
> +++ b/drivers/staging/pi433/rf69.c
> @@ -255,17 +255,29 @@ int rf69_set_deviation(struct spi_device *spi, u32 deviation)
> int retval;
> u64 f_reg;
> u64 f_step;
> + u32 bit_rate_reg;
> + u32 bit_rate;
> u8 msb;
> u8 lsb;
> u64 factor = 1000000; // to improve precision of calculation
>
> - // TODO: Dependency to bitrate
> - if (deviation < 600 || deviation > 500000) {
> - dev_dbg(&spi->dev, "set_deviation: illegal input param");
> + // calculate bit rate
> + bit_rate_reg = rf69_read_reg(spi, REG_BITRATE_MSB) << 8;
> + bit_rate_reg |= rf69_read_reg(spi, REG_BITRATE_LSB);
> + bit_rate = F_OSC / bit_rate_reg;
> +
> + /*
> + * frequency deviation must exceed 600 Hz and but not exceed
> + * 500kHz when taking bitrate dependency into consideration
> + * to ensure proper modulation
> + */
> + if (deviation < 600 || (deviation + (bit_rate / 2)) > 500000) {
> + dev_dbg(&spi->dev,
> + "set_deviation: illegal input param: %u", deviation);
> return -EINVAL;
> }

this should go in a separate patch IMO

>
> - // calculat f step
> + // calculate f step
> f_step = F_OSC * factor;
> do_div(f_step, 524288); // 524288 = 2^19
>
> --
> 2.25.4
>
>

thank you,

fabio

2022-01-03 13:27:18

by Greg Kroah-Hartman

Subject: Re: [PATCH] staging: pi433: fix frequency deviation check

On Mon, Jan 03, 2022 at 09:11:35PM +1300, Paulo Miguel Almeida wrote:
> rf69 datasheet states that frequency deviation must exceed 600 Hz but
> also that frequency deviation + (bitrate / 2) should be less than equal
> to 500 kHz to ensure proper modulation.
>
> This patch validates that both conditions are met so RF intersymbol
> interference is "avoided" where possible.
>
> Signed-off-by: Paulo Miguel Almeida <[email protected]>
> ---
> drivers/staging/pi433/rf69.c | 20 ++++++++++++++++----
> 1 file changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/staging/pi433/rf69.c b/drivers/staging/pi433/rf69.c
> index e62e61ef4d27..cc22915fd489 100644
> --- a/drivers/staging/pi433/rf69.c
> +++ b/drivers/staging/pi433/rf69.c
> @@ -255,17 +255,29 @@ int rf69_set_deviation(struct spi_device *spi, u32 deviation)
> int retval;
> u64 f_reg;
> u64 f_step;
> + u32 bit_rate_reg;
> + u32 bit_rate;
> u8 msb;
> u8 lsb;
> u64 factor = 1000000; // to improve precision of calculation
>
> - // TODO: Dependency to bitrate
> - if (deviation < 600 || deviation > 500000) {
> - dev_dbg(&spi->dev, "set_deviation: illegal input param");
> + // calculate bit rate
> + bit_rate_reg = rf69_read_reg(spi, REG_BITRATE_MSB) << 8;
> + bit_rate_reg |= rf69_read_reg(spi, REG_BITRATE_LSB);
> + bit_rate = F_OSC / bit_rate_reg;
> +
> + /*
> + * frequency deviation must exceed 600 Hz and but not exceed
> + * 500kHz when taking bitrate dependency into consideration
> + * to ensure proper modulation
> + */
> + if (deviation < 600 || (deviation + (bit_rate / 2)) > 500000) {
> + dev_dbg(&spi->dev,
> + "set_deviation: illegal input param: %u", deviation);
> return -EINVAL;
> }
>
> - // calculat f step
> + // calculate f step

This change should be a separate patch.

thanks,

greg k-h

2022-01-03 22:23:42

by Paulo Miguel Almeida

Subject: [PATCH v2] staging: pi433: fix frequency deviation check

rf69 datasheet states that frequency deviation must exceed 600 Hz but
also that frequency deviation + (bitrate / 2) should be less than equal
to 500 kHz to ensure proper modulation.

This patch validates that both conditions are met so RF intersymbol
interference is less likely to happen due to misconfiguration of the uC

Signed-off-by: Paulo Miguel Almeida <[email protected]>
---
v2: remove typo correction from this patch - Req Greg k-h, Fabio A.
v1: https://lore.kernel.org/lkml/[email protected]/
---
drivers/staging/pi433/rf69.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/pi433/rf69.c b/drivers/staging/pi433/rf69.c
index e62e61ef4d27..d64df072d8e8 100644
--- a/drivers/staging/pi433/rf69.c
+++ b/drivers/staging/pi433/rf69.c
@@ -255,13 +255,25 @@ int rf69_set_deviation(struct spi_device *spi, u32 deviation)
int retval;
u64 f_reg;
u64 f_step;
+ u32 bit_rate_reg;
+ u32 bit_rate;
u8 msb;
u8 lsb;
u64 factor = 1000000; // to improve precision of calculation

- // TODO: Dependency to bitrate
- if (deviation < 600 || deviation > 500000) {
- dev_dbg(&spi->dev, "set_deviation: illegal input param");
+ // calculate bit rate
+ bit_rate_reg = rf69_read_reg(spi, REG_BITRATE_MSB) << 8;
+ bit_rate_reg |= rf69_read_reg(spi, REG_BITRATE_LSB);
+ bit_rate = F_OSC / bit_rate_reg;
+
+ /*
+ * frequency deviation must exceed 600 Hz but not exceed
+ * 500kHz when taking bitrate dependency into consideration
+ * to ensure proper modulation
+ */
+ if (deviation < 600 || (deviation + (bit_rate / 2)) > 500000) {
+ dev_dbg(&spi->dev,
+ "set_deviation: illegal input param: %u", deviation);
return -EINVAL;
}

--
2.25.4

2022-01-03 22:28:21

by Paulo Miguel Almeida

Subject: Re: [PATCH] staging: pi433: fix frequency deviation check

On Mon, Jan 03, 2022 at 02:27:10PM +0100, Greg KH wrote:
> On Mon, Jan 03, 2022 at 09:11:35PM +1300, Paulo Miguel Almeida wrote:
> > - // calculat f step
> > + // calculate f step
>
> This change should be a separate patch.
>

Thanks Fabio and Greg for reviewing my patch. I just sent a v2 of this
patch with that line untouched.

thanks,

Paulo A.