nRF52832 Product Specification V1.4, page 344 lists predefined baud rates only.
Is it possible to use other values for custom baud rate, and if so, what is the relationship between the Value and the actual generated baud rate?
nRF52832 Product Specification V1.4, page 344 lists predefined baud rates only.
Is it possible to use other values for custom baud rate, and if so, what is the relationship between the Value and the actual generated baud rate?
Such a good question, and highlights the fun the hardware design engineer must have been having that day .. this is what I use, inclusive of the rounding
// Baud rate calculation on nRF51 and nRF52832 // =========================================== // // Calculate BAUDRATE value settings for the black-magic 20-bit baud rate generator uint32_t CalculatedRegisterValue; uint64_t SystemClock = 16000000ULL; // Typically 16MHz uint64_t MagicScaler = 32; // Preserves bits on divisions, shift 32 bits // Baudrate generator for the UART is the top 20 bits of a 32-bit field; add in rounding 0.5 ls bit CalculatedRegisterValue = (uint32_t)((((uint64_t)RequiredBaudRate << MagicScaler) / SystemClock) + 0x800) & 0xFFFFF000;
So does it work? Well it doesn't exactly match the datasheet quoted values:
typedef struct {
uint32_t QuotedRegisterValue;
uint32_t RequiredBaudRate;
uint32_t QuotedActualBaudRate;
} BaudCheck_t;
// Quoted values from nRF52832 v1.4 datasheet
static BaudCheck_t BaudCheck[] = {
{0x0004F000, 1200, 1205},
{0x0009D000, 2400, 2396},
{0x0013B000, 4800, 4808},
{0x00275000, 9600, 9598},
{0x003AF000, 14400, 14401},
{0x004EA000, 19200, 19208},
{0x0075C000, 28800, 28777},
{0x009D0000, 38400, 38369},
{0x00EB0000, 57600, 57554},
{0x013A9000, 76800, 76923},
{0x01D60000, 115200, 115108},
{0x03B00000, 230400, 231884},
{0x04000000, 250000, 250000},
{0x07400000, 460800, 457143},
{0x0F000000, 921600, 941176},
{0x10000000, 1000000, 1000000}};
#define NUM_BAUD_TESTS (sizeof(BaudCheck)/sizeof(BaudCheck[0]))
static void BaudRateDivisorTest(void)
{
// Baud rate calculation on nRF51 and nRF52832
// ===========================================
//
// Calculate BAUDRATE value settings for the black-magic 20-bit baud rate generator
uint32_t OkCountRegister = 0, FailCountRegister = 0, CalculatedRegisterValue;
uint32_t OkCountActualBaud = 0, FailCountActualBaud = 0;
uint32_t BaudIndex, ActualBaudRate;
uint64_t SystemClock = 16000000ULL; // Typically 16MHz
uint64_t MagicScaler = 32; // Preserves bits on divisions, shift 32 bits
for (BaudIndex = 0; BaudIndex < NUM_BAUD_TESTS; BaudIndex++)
{
// Baudrate generator for the UART is the top 20 bits of a 32-bit field; add in rounding 0.5 ls bit
CalculatedRegisterValue = (uint32_t)((((uint64_t)BaudCheck[BaudIndex].RequiredBaudRate << MagicScaler) / SystemClock) + 0x800) & 0xFFFFF000;
if ( BaudCheck[BaudIndex].QuotedRegisterValue == CalculatedRegisterValue)
{
OkCountRegister++;
}
else
{
FailCountRegister++;
}
ActualBaudRate = (uint32_t)(((uint64_t)CalculatedRegisterValue * SystemClock) >> MagicScaler);
if ( BaudCheck[BaudIndex].QuotedActualBaudRate == ActualBaudRate)
{
OkCountActualBaud++;
}
else
{
FailCountActualBaud++;
}
}
while(1) ;
}
The values either exactly match the data sheet or are close; that may be a code issue or a datasheet issue, who knows but I think the h/w guy was teasing us..
I checked the nRF52840 Product Specification, and interestingly there have been some additions and corrections, but 10 of the 26 quoted values still seem incorrect, although now not by much. I'm also curious as to whether the baud rate generator is indeed only 20 bits, given that all 32 bits are writable .. I may test this if I get time.
// 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
I added rounding on the system clock, but that doesn't affect results:
// Baudrate generator for the UART is the top 20 bits of a 32-bit field; add in rounding 0.5 ls bit CalculatedRegisterValue = (uint32_t)(((((uint64_t)RequiredBaudRate << MagicScaler) + (SystemClock >> 1)) / SystemClock) + 0x800) & 0xFFFFF000;
nRF52832 (rev 2) NRF_UARTE0->BAUDRATE values and corresponding baud rates.
Bits 11-0 are not used.
nrf52832_uarte_baud_rates.txt
Hi hmolesworth,
Thank you so much!
The equation :
CalculatedRegisterValue = (uint32_t)((((uint64_t)RequiredBaudRate << MagicScaler) + (SystemClock>>1) / SystemClock) + 0x800) & 0xFFFFF000;
should be modified as following in my SES IDE :
CalculatedRegisterValue = (uint32_t)(( ( ((uint64_t)RequiredBaudRate << MagicScaler) + (SystemClock>>1) )/ SystemClock) + 0x800) & 0xFFFFF000;
Good catch!
FYI: We've finished some loopback test, when buadrate is set to 2Mbps, no data can be received and no events can be triggered, however when baudrate is set to 2.5Mbps, some events can be triggered according to TX data, maybe we can use it to build a special full-duplex system.
I tested Tx up to a tad less than 8MHz (7.99999MHz) and Tx works fine, but the Rx probably uses /16 or /3 for voting on high/low for each bit; I posted the baud rates I tested on Tx here some years ago framing-error-and-noisy-data-when-using-uarte-at-high-baud-rate
Might be worth us doing a loopback test at all baud rates, maybe run overnight ..
I tested Tx up to a tad less than 8MHz (7.99999MHz) and Tx works fine, but the Rx probably uses /16 or /3 for voting on high/low for each bit; I posted the baud rates I tested on Tx here some years ago framing-error-and-noisy-data-when-using-uarte-at-high-baud-rate
Might be worth us doing a loopback test at all baud rates, maybe run overnight ..
We've finished more loopback tests. It shows 2.5Mbps with RX buffer length=1(>1 can't) can work well, 1.5Mbps(1.6Mbps can't) with RX buffer length=64(>64 should OK too) can work well. We guest there is some unknown factor causing the strange results. For our application, 2.5Mbps with RX buffer length=1 is OK. Thank you for your great contribution!
Helpful feedback, and I verified 1.5MHz. Following on, it looks like the receiver is using a 9-sample mechanism for voting on each received bit. MSP430 uses 3 samples, older uarts use 16 samples. For 9 samples, at least 5 high samples are required for deciding a '1', ditto 5 or more low for a '0'. 16MHz / 9 => 1.777778 MHz. Setting this value as the baud rate gives zero errors in 256-byte packets (8N1). I'll run a test with (say) 4 k packet sizes, but this is good news.
I spent a while longer on this, and have some helpful information.
First the single UART/E on the nRF52832 and both the UART/Es on the nRF52840 can be used in loopback mode (with or without DMA) with a single pin and no jumper wires; this is useful for testing, 1-wire applications and RS485. Second the max value for large packets seems to be 1,777,760 baud register 1C71'B000 which I verified by loopback testing of 2048-byte packets on the nRF52840 and 128-byte packets on the nRF52832 and checking for framing and other errors.
This is the bare-metal code in case it is useful to others:
static void SetupUART(const uint32_t BaudRate);
static void StartUART_Transmit(const uint8_t * const pMsg, const uint16_t MsgLength);
static void DisableUART(void);
static uint16_t SetupUART_Receive(uint8_t * const pMsg, const uint16_t MaxMsgLength);
static uint16_t WaitUART_Receive(void);
static NRF_UARTE_Type *pUART = NRF_UARTE0;
#define PIN_UART_TX PIN_FEATHER_TXD
#define PIN_UART_RX PIN_FEATHER_RXD
#define MAX_TX_PACKET_SIZE 2048 // 16-bit on nRF52840, only 8-bit on nRF52832
static uint8_t TxMsg[MAX_TX_PACKET_SIZE] = "Baudrate generator for the UART is the top 20 bits of a 32-bit field; add in rounding 0.5 ls bit";
#define TX_PACKET_SIZE sizeof(TxMsg)
#define RX_PACKET_SIZE (TX_PACKET_SIZE - 1)
static uint8_t RxMsg[RX_PACKET_SIZE] = "";
uint32_t RequiredBaudRate = 1000000UL;
uint32_t MaxOkdBaudRate = 0UL;
uint32_t CalculatedRegisterValue;
uint32_t RegisterValueAtMaxBaud = 0;
uint64_t SystemClock = 16000000ULL; // Typically 16MHz
uint64_t MagicScaler = 32; // Preserves bits on divisions, shift 32 bits
void UART_BaudTest(void)
{
// Enable crystal osc
for (RequiredBaudRate = 1000000; RequiredBaudRate < 8000000; )
{
// Baudrate generator for the UART is the top 20 bits of a 32-bit field; add in rounding 0.5 ls bit
CalculatedRegisterValue = (uint32_t)(((((uint64_t)RequiredBaudRate << MagicScaler) + (SystemClock >> 1)) / SystemClock) + 0x800) & 0xFFFFF000;
// Setup UART from scratch for each baud rate test
SetupUART(CalculatedRegisterValue);
SetupUART_Receive(RxMsg, sizeof(RxMsg));
StartUART_Transmit(TxMsg, TX_PACKET_SIZE);
WaitUART_Receive();
DisableUART();
if ((memcmp(TxMsg, RxMsg, RX_PACKET_SIZE) == 0) && (pUART->EVENTS_ERROR == 0) && (pUART->ERRORSRC == 0x0000))
{
MaxOkdBaudRate = RequiredBaudRate;
RegisterValueAtMaxBaud = CalculatedRegisterValue;
}
RequiredBaudRate += 20;
}
while (1)
;
}
static void SetupUART(const uint32_t BaudRate)
{
// Disable the UARTE
pUART->ENABLE = 0;
// Configure UARTE with no flow control, no parity bit and selected baud rate
pUART->CONFIG = 0;
pUART->BAUDRATE = BaudRate;
// Select TX and RX pin default disconnected mode to avoid sending break indication on disabling uart
nrf_gpio_cfg(PIN_UART_RX, NRF_GPIO_PIN_DIR_INPUT, NRF_GPIO_PIN_INPUT_CONNECT, NRF_GPIO_PIN_PULLUP, NRF_GPIO_PIN_S0S1, NRF_GPIO_PIN_NOSENSE);
nrf_gpio_cfg(PIN_UART_TX, NRF_GPIO_PIN_DIR_OUTPUT, NRF_GPIO_PIN_INPUT_CONNECT, NRF_GPIO_PIN_PULLUP, NRF_GPIO_PIN_H0H1, NRF_GPIO_PIN_NOSENSE);
// Select TX and RX pins; note for Loopback testing or 1-wire or RS485 a single pin can be used for both Rx and Tx
pUART->PSEL.TXD = PIN_UART_TX;
pUART->PSEL.RXD = PIN_UART_RX; // For single pin loopback use PIN_UART_TX here
// Disable all interrupts and clear events
pUART->INTENCLR = 0xFFFFFFFFUL;
pUART->EVENTS_TXSTARTED = 0;
pUART->EVENTS_TXSTOPPED = 0;
pUART->EVENTS_RXSTARTED = 0;
pUART->EVENTS_ERROR = 0;
pUART->ERRORSRC = 0x000F; // Write '1's to clear any errors left set
pUART->EVENTS_ENDTX = 0;
pUART->EVENTS_ENDRX = 0;
// Enable the UART, note 0x04 for UART and 0x08 for UARTE with DMA
pUART->ENABLE = 0x08;
}
STATIC_ASSERT (UARTE_ENABLE_ENABLE_Enabled == 0x08, "UARTE_ENABLE_ENABLE_Enabled == 0x08 Failed");
static void StartUART_Transmit(const uint8_t * const pMsg, const uint16_t MsgLength)
{
// Configure transmit buffer and start the transfer
pUART->TXD.MAXCNT = MsgLength;
pUART->TXD.PTR = (uint32_t)pMsg;
pUART->TASKS_STARTTX = 1;
__DSB();
// Wait until the transfer start event is indicated
while (pUART->EVENTS_TXSTARTED == 0) ;
// Wait until the transfer is complete
while (pUART->EVENTS_ENDTX == 0) ;
// Stop the UART TX
pUART->TASKS_STOPTX = 1;
__DSB();
// Wait until we receive the stopped event
while (pUART->EVENTS_TXSTOPPED == 0) ;
}
static void DisableUART(void)
{
// Disable the UARTE
pUART->ENABLE = 0;
// De-Select TX and RX pins
pUART->PSEL.TXD = 0x80000000;
pUART->PSEL.RXD = 0x80000000;
}
static uint16_t SetupUART_Receive(uint8_t * const pMsg, const uint16_t MaxMsgLength)
{
volatile uint32_t Timeout;
// Clear receive buffer
memcpy(pMsg, "-----------------", MaxMsgLength);
// Configure receive buffer and start reception
pUART->RXD.MAXCNT = MaxMsgLength;
pUART->RXD.PTR = (uint32_t)pMsg;
pUART->EVENTS_ENDRX = 0;
pUART->TASKS_STARTRX = 1;
__DSB();
// Wait until the transfer start event is indicated
while (pUART->EVENTS_RXSTARTED == 0) ;
return 0;
}
static uint16_t WaitUART_Receive(void)
{
// Wait until the transfer is complete
//while (pUART->EVENTS_ENDRX == 0) ; //add timeout here if using this during tests
// just delay .. not actually required but helps with testing
nrf_delay_ms(1);
// Stop the UART RX
pUART->TASKS_STOPRX = 1;
__DSB();
// Wait until we receive the stopped event
//while (pUART->EVENTS_ENDRX == 0) ;
// Flush fifo
//pUART->TASKS_FLUSHRX = 1;
// Return packet when postLastRxByteTime indicates end-of-packet timeout
return 0;
}
Good Job! The mechanism for receiver to identify the first byte seems more complicated, need more efforts to understand it, we'll do more test in future.