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Allow any baud rate; not just a restricted set #41

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Allow any baud rate; not just a restricted set #41

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Timmmm
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@Timmmm Timmmm commented Jan 22, 2016

Fixes #40.

I'm pretty sure the rounding is unnecessary (i.e. the hardware rounds / truncates anyway), but I did it anyway so the values match the Nordic header.

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Allow any baud rate; not just a restricted set
80af320 
Fixes ARMmbed#40.

I'm pretty sure the rounding is unnecessary (i.e. the hardware rounds / truncates anyway), but I did it anyway so the values match the Nordic header.
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0xc0170 commented Mar 1, 2016

@emidttun @pan-

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ciarmcom commented Mar 1, 2016

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emidttun
emidttun reviewed Mar 3, 2016
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source/serial_api.c
// Round it to 20 bits (see link above).
br = (br + 0x800) & 0xFFFFF000;

// Limit it to the valid range.
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Where is the valid range defined? From the nRF51 ref manual any 32-bit value seems to be accepted.

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Timmmm commented Mar 4, 2016

Here is the code I used to test it. It's Matlab/Octave rather than C, but it is the same maths.

function code = ToBaudCode(br)

code = bitshift(br, 8, 32) ...
+ bitshift(br, 4, 32)...
 - bitshift(br, 1, 32)...
 - br...
 - bitshift(br, -1, 32)...
 - bitshift(br, -4, 32)...
 - bitshift(br, -9, 32)...
 - bitshift(br, -14, 32)...
 - bitshift(br, -16, 32)...
 - bitshift(br, -17, 32)...
 - bitshift(br, -18, 32)...
 - bitshift(br, -19, 32);

 % Round it
 code = bitand(code + 0x800, 0xFFFFF000);

 end

Test:

bauds = [1200 2400 4800 9600 14400 19200 28800 38400 57600 76800 115200 230400 250000 460800 921600 1000000];
for ff = bauds
    dec2hex(ToBaudCode(ff))
end

Output:

ans = 4F000
ans = 9D000
ans = 13B000
ans = 275000
ans = 3B0000
ans = 4EA000
ans = 75F000
ans = 9D5000
ans = EBF000
ans = 13A9000
ans = 1D7E000
ans = 3AFB000
ans = 4000000
ans = 75F7000
ans = EBEE000
ans = 10000000

Correct values:

#define UART_BAUDRATE_BAUDRATE_Baud1200 (0x0004F000UL) /*!< 1200 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud2400 (0x0009D000UL) /*!< 2400 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud4800 (0x0013B000UL) /*!< 4800 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud9600 (0x00275000UL) /*!< 9600 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud14400 (0x003B0000UL) /*!< 14400 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud19200 (0x004EA000UL) /*!< 19200 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud28800 (0x0075F000UL) /*!< 28800 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud38400 (0x009D5000UL) /*!< 38400 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud57600 (0x00EBF000UL) /*!< 57600 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud76800 (0x013A9000UL) /*!< 76800 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud115200 (0x01D7E000UL) /*!< 115200 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud230400 (0x03AFB000UL) /*!< 230400 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud250000 (0x04000000UL) /*!< 250000 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud460800 (0x075F7000UL) /*!< 460800 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud921600 (0x0EBED000UL) /*!< 921600 baud. */
#define UART_BAUDRATE_BAUDRATE_Baud1M (0x10000000UL) /*!< 1M baud. */

Looks like the 921600 value has been rounded in the latest code. My value is very slightly different, but it shouldn't matter in practice (it's a 0.002% difference).

It seems pretty clear from the datasheet to me that the maximum rate is 1 Mbaud, especially as 1 Mbaud gets a special value (0x10000000). The minimum rate is due to the rounding (I don't think anyone will want to go as low as 15 baud anyway!).

@Timmmm Timmmm closed this Aug 8, 2024
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Only specific baud rates allowed, but chip supports any.
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@Timmmm @ciarmcom @0xc0170 @emidttun