Uart baud rate 512

RE: Uart baud rate 512

Einar Thorsrud — Tue, 04 Oct 2022 08:18:19 GMT

Hi Magnus,

That is right. The formula from the old post (describing the UART peripheral in the nRF51 series) is not entirely valid, as is also stated in the post - "this formula is simplified".

RE: Uart baud rate 512

MagnusPersson — Tue, 04 Oct 2022 08:14:32 GMT

OK, thanks. One more question: Does this mean that the formula suggested in this ancient post linked above to calculate the values for the BAUDRATE register and the actual baud rate is actually not valid?

Anyway, I guess the difference should be within the fault tolerance of any system using start and stop bits properly.

Thanks,

-Magnus

RE: Uart baud rate 512

Einar Thorsrud — Tue, 04 Oct 2022 07:37:50 GMT

Hi Magnus,

[quote user="MagnusPersson"]It would be interesting to get a background to the numbers in the Product Specification.[/quote]

This has to do with the way the different frequencies are generated within the nRF (derived from the HF clock), and the provided values are the closest you can get. I cannot comment on the implementation details, unfortunately.

[quote user="MagnusPersson"]Would also be interesting to know why the register numbers for UART and UARTE differs in the Product Specification.[/quote]

There are some implementation differences between those peripherals (though they share a lot and in fact overlap physically), but this is not publicly documented and I cannot comment on the details.

RE: Uart baud rate 512

MagnusPersson — Mon, 03 Oct 2022 17:06:24 GMT

Thanks a lot. so if I understand your tables I have calculated correctly and the Nordic quoted numbers in the code and Product Specification differ from our understanding.

It would be interesting to get a background to the numbers in the Product Specification.

Would also be interesting to know why the register numbers for UART and UARTE differs in the Product Specification.

Thanks,

-Magnus

RE: Uart baud rate 512

hmolesworth — Mon, 03 Oct 2022 15:49:30 GMT

There is a 2% error in the documented baud rate for 921600 baud:

// Quoted values from nRF52832 v1.4 datasheet - 16 correct, 10 incorrect
static BaudCheck_t BaudCheck[] = {
//  -------Documentation---------   -------Calculated---------
//  Register    Required   Actual    Register    Actual    Ok?      Index
//  ==========  ========   ======   ==========   ======   ====      =====
   {0x0004F000,     1200,    1205,  0x0004F000,    1205, " Ok"},  //  0
   {0x0009D000,     2400,    2396,  0x0009D000,    2395, " Ok"},  //  1
   {0x0013B000,     4800,    4808,  0x0013B000,    4806, " Ok"},  //  2
   {0x00275000,     9600,    9598,  0x00275000,    9597, " Ok"},  //  3
   {0x003AF000,    14400,   14401,  0x003B0000,   14404, "  -"},  //  4
   {0x004EA000,    19200,   19208,  0x004EA000,   19195, " Ok"},  //  5
   {0x0075C000,    28800,   28777,  0x0075F000,   28793, "  -"},  //  6
   {0x009D0000,    38400,   38369,  0x009D5000,   38406, "  -"},  //  7
   {0x00EB0000,    57600,   57554,  0x00EBF000,   57601, "  -"},  //  8
   {0x013A9000,    76800,   76923,  0x013A9000,   76797, " Ok"},  //  9
   {0x01D60000,   115200,  115108,  0x01D7E000,  115203, "  -"},  // 10
   {0x03B00000,   230400,  231884,  0x03AFB000,  230392, "  -"},  // 11
   {0x04000000,   250000,  250000,  0x04000000,  250000, " Ok"},  // 12
   {0x07400000,   460800,  457143,  0x075F7000,  460800, "  -"},  // 13
   {0x0F000000,   921600,  941176,  0x0EBEE000,  921600, "  -"},  // 14
   {0x10000000,  1000000, 1000000,  0x10000000, 1000000, " Ok"},  // 15
// Extra and changed values from nRF52840 Product Specification
   {0x003B0000,    14400,   14414,  0x003B0000,   14404, " Ok"},  // 16
   {0x0075F000,    28800,   28829,  0x0075F000,   28793, " Ok"},  // 17
   {0x00800000,    31250,   31250,  0x00800000,   31250, " Ok"},  // 18
   {0x009D5000,    38400,   38462,  0x003B0000,   38406, " Ok"},  // 19
   {0x00E50000,    56000,   55944,  0x00E56000,   55999, "  -"},  // 20
   {0x00EBF000,    57600,   57762,  0x00EBF000,   57601, " Ok"},  // 21
   {0x01D7E000,   115200,  115942,  0x01D7E000,  115203, " Ok"},  // 22
   {0x03AFB000,   230400,  231884,  0x03AFB000,  230392, " Ok"},  // 23
   {0x075F7000,   460800,  470588,  0x075F7000,  460800, " Ok"},  // 24
   {0x0EBED000,   921600,  941176,  0x0EBEE000,  921600, "  -"}}; // 25
#define NUM_BAUD_TESTS (sizeof(BaudCheck)/sizeof(BaudCheck[0]))

This link shows my calculations: uart-baud-rate-generator which can be used to get 512 baud

Updated for v1.7 datasheet framing-error-and-noisy-data-when-using-uarte-at-high-baud-rate

RE: Uart baud rate 512

MagnusPersson — Mon, 03 Oct 2022 11:19:05 GMT

Sorry about digging up an old post here.

With regards to the values in the UART_BAUDRATE register I have a hard time match the "actual rate" in the nrf52_bitfields.h with the formula given.

#define UART_BAUDRATE_BAUDRATE_Baud921600 (0x0EBED000UL) /*!< 921600 baud (actual rate: 941176) */

0x0EBED000 * 16000000 / 2^32 = 921585

Did I miscalculate or misunderstand anything?

Thx,

-Magnus

RE: Uart baud rate 512

awneil — Thu, 11 Apr 2019 10:44:35 GMT

[quote userid="2137" url="~/f/nordic-q-a/46025/uart-baud-rate-512/181341"]On 52832 side I am not able to receive a single byte. There happens nothing[/quote]

So what testing / debugging / investigation have you done to find out why?

Again, do you see any activity at all when you transmit from the nRF? If so, is the baud rate correct?

If your external MCU is using such a weird baud rate, is it also doing other weird things - like inverting the data, or using a weird frame format ...?

RE: Uart baud rate 512

awneil — Thu, 11 Apr 2019 10:40:57 GMT

At such a low baud rate, a software (bit-banged) UART may be practical ... ?

RE: Uart baud rate 512

Einar Thorsrud — Thu, 11 Apr 2019 10:37:00 GMT

Hi,

512 is not a supported baud rate. You can always try to play with the BAUDRATE register but using anything other than the listed baud rates may or may not work. You can refer to this ancient post to see an explanation on the BAUDRATE register (it is the same for the UARTE peripheral on the nRF52 series).

RE: Uart baud rate 512

Fritz Kendeffy-Hermann — Wed, 10 Apr 2019 13:17:10 GMT

I am not able to change the FW of the device where the nrf52832 is connected to. So I need go get it work with baud rate 512.

The uart communication (same code) was working before with normal baud rate in another project.

When I connect TX of the connected mcu via serial adapter to my PC, I am able to monitor what it is sending.

On 52832 side I am not able to receive a single byte. There happens nothing

RE: Uart baud rate 512

awneil — Wed, 10 Apr 2019 12:50:03 GMT

Have you checked in the Product Specification ?

512 is not a "normal" baud rate - why do you need that, specifically?

Have you verified that your setup works with a "normal" baud rate?

[quote userid="2137" url="~/f/nordic-q-a/46025/uart-baud-rate-512"]I tried to configure the uart with this baud rate, but I am not able to get the uart communication working[/quote]

So what, exactly, did you do?

And what, exactly, was the result?

Do you see any activity at all on transmit?