Low level UART using the Registers

[PoojaK]

Hi,

I am trying to write my own uart init and irq handler routines by accessing the registers directly as per the data sheet. I also referred to https://devzone.nordicsemi.com/f/nordic-q-a/48107/low-level-uart-and-timer-drivers this query on devzone and saw the libuarte code but I believe it is software simulated UART code.

 Here is my piece of code

#define UART0_RX  8
#define UART0_TX  6
#define UART0_CTS 7
#define UART0_RTS 5

void uart0Init()
{
  NRF_UARTE0->PSEL.RXD = UART0_RX ;
  NRF_UARTE0->PSEL.TXD = UART0_TX ;
  NRF_UARTE0->PSEL.CTS = UART0_CTS ;
  NRF_UARTE0->PSEL.RTS = UART0_RTS ;
  NRF_UARTE0->BAUDRATE = 0x01D60000 ;  //115200 Baud
  NRF_UARTE0->INTEN = 0x00000104 ;  //Enable RXDRDY and ENDTX interrupt

}

. 

What I want is that where should I write my own IRQ routine so that my code will be directed to this isr like in other MCUs . I also tried doing this: 

#define UART0_IRQHandler        UARTE0_UART0_IRQHandler
#define UART1_IRQHandler        UARTE1_UART1_IRQHandler


void UART0_IRQHandler()
{
  //process my isr
}

But it is giving me an error saying multiple definitions of UARTE0 and UARTE1 detected. 

I only need Transmit Complete interrupt and Receive Buffer Ready or No Ready interrupt. And need to write my own code for what to do when I get these interrupts.

Please help me get a solution to this

[hmolesworth]

Try simply disabling all the library uart code; search for "_ENABLED 1" and check all the hits in sdk_config.h; then change them all to '0'. Some examples 

#define UART_ENABLED 1
#define UART_0_ENABLED 1
#define NRFX_UART_ENABLED 1
#define NRFX_UARTE_ENABLED 1

change to

#define UART_ENABLED 0
#define UART_0_ENABLED 0
#define NRFX_UART_ENABLED 0
#define NRFX_UARTE_ENABLED 0

There are a lot, depending on where the file came from; there are also multiple instances in some files. The goal is then to use the handler defined as weak so it will be eclipsed by your handler

void UARTE0_UART0_IRQHandler(void)
{
}

The nrf and nrfx uart files can also be removed from the build as they will no longer be used

[PoojaK]

Okay Great! Now I am not getting any errors for my irq. 

Now I will try my own code.

Thanks a Lot.

[PoojaK]

It is compiling without any errors now. 

But now I am not getting how to transmit my data using TXD and receive using RXD . Because the data sheet only specifies .PTR .MAXCOUNT and .AMOUNT 

Where do I write my actual data to be transmitted and received.

The data sheet says:

The first step of a DMA transmission is storing bytes in the transmit buffer and configuring EasyDMA. This
is achieved by writing the initial address pointer to TXD.PTR, and the number of bytes in the RAM buffer to
TXD.MAXCNT. The UARTE transmission is started by triggering the STARTTX task.
"After each byte has been sent over the TXD line, a TXDRDY event will be generated."
When all bytes in the TXD buffer, as specified in the TXD.MAXCNT register, have been transmitted, the
UARTE transmission will end automatically and an ENDTX event will be generated.
A UARTE transmission sequence is stopped by triggering the STOPTX task, a TXSTOPPED event will be
generated when the UARTE transmitter has stopped.

But I dont know how am I supposed to send data bytes on TXD line.

There is no register that will do NRF_UARTE0->TXD = 0xAA (or any other data that I want to transmit)

Please help me out with this

[Vidar Berg]

Hi,

Have you considered using the UART driver instead? It should be a lot easier to set-up, so that is what I would recommend.

PoojaK said:

But I dont know how am I supposed to send data bytes on TXD line.

 You need to set up a RAM buffer with the TX data you want to send, then load the pointer to that buffer into .TXD.PTR and the buffer size into TXD.AMOUNT

[hmolesworth]

Here is a simple low-level function for Tx uart/main.c. Rx is always more involved, unless you accept simple character-by-character reception. I don't have an example to hand