SPI read and write multiple bytes of varying lengths with MCP2515

RE: SPI read and write multiple bytes of varying lengths with MCP2515

hmolesworth — Mon, 16 Sep 2019 21:57:33 GMT

Try correcting this error and see if that helps:

void mcp2515_spi_transfer(uint8_t p_tx_data, uint8_t p_rx_data, const uint16_t len)
{
    // Reset rx buffer and transfer done flag
    memset(&p_rx_data, 0, len);
    
    NRF_LOG_INFO("tx data %x\n", p_tx_data);

    APP_ERROR_CHECK(nrf_drv_spi_transfer(&can_spi, &p_tx_data, len, &p_rx_data, len));

Should be

void mcp2515_spi_transfer(uint8_t *p_tx_data, uint8_t *p_rx_data, const uint16_t len)
{
    // Reset rx buffer and transfer done flag
    memset(p_rx_data, 0, len);
    
    NRF_LOG_INFO("tx data %x\n", p_tx_data);

    APP_ERROR_CHECK(nrf_drv_spi_transfer(&can_spi, p_tx_data, len, p_rx_data, len));

In the first case you are using the address of a byte parameter on the stack, not the address of the buffers you require.

You might also try increasing the drive of the SCK output pin to H0H1, just until you have everything working. This must be done after initialising the SPI which sets that output pin to S0S1. If the CAN chip is off-board maybe long leads or capacitance issues are corrupting transfers, although unlikely at 250kHz

RE: SPI read and write multiple bytes of varying lengths with MCP2515

BendaEng — Mon, 16 Sep 2019 20:23:58 GMT

I have tried to analyze the SPI lines using an SDS 1104X-E scope. I don't see any data coming out, only 0x00 on the MISO line. For the first section however (initialization of MCP2515) I get the following readout (This is based on the attached main.c and mcp_can.c/h and mcp_can_dfs.h which I've modified):

<info> app: Template example started.
<info> app: Fast advertising.
<info> app: CAN SPI example started.
<info> app: Start

<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Enter setting mode success 

<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: set rate success!!

<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Transfer completed.
<info> app: Enter Normal Mode Success!!

<info> app: CAN initialization ok

<info> app: Transfer completed.
<info> app: Data Received 0 0x0
<info> app: Data Received 1 0x0
<info> app: Data Received 2 0x0
<info> app: Data Received 3 0x3
<info> app: Data Received 4 0x3
<info> app: Transfer completed.
<info> app: Data Received 0 0x0
<info> app: Data Received 1 0x0
<info> app: Data Received 2 0x0
<info> app: Data Received 3 0x3
<info> app: Data Received 4 0x3
<info> app: Transfer completed.
<info> app: Data Received 0 0x0
<info> app: Data Received 1 0x0
<info> app: Data Received 2 0x0
<info> app: Data Received 3 0x3
<info> app: Data Received 4 0x3
<info> app: Transfer completed.


...//This repeats

devzone.nordicsemi.com/.../2474.mcp_5F00_can.c devzone.nordicsemi.com/.../mcp_5F00_can.h devzone.nordicsemi.com/.../mcp_5F00_can_5F00_dfs.h devzone.nordicsemi.com/.../2867.main.c

I think I'm getting through the initialization because the setup is checking if the received is 0x00, which is what I'm only getting. What could be a cause of no response from the MCP2515 do you think?

Thanks!

RE: SPI read and write multiple bytes of varying lengths with MCP2515

Edvin — Mon, 16 Sep 2019 11:38:03 GMT

Have you tried to analyze the SPI lines with a logic analyzer? Is there any data coming from the device? Or is it flat at GND?

RE: SPI read and write multiple bytes of varying lengths with MCP2515

BendaEng — Thu, 12 Sep 2019 18:32:52 GMT

Well I had been doing this. But adding 2 to the length (2+5) returns all zeros (0x0 for all).

// Enter main loop.
    for (;;)
    {
        uint8_t values[5]; 
        mcp2515_readRegisterS(MCP_READ_STATUS, values, 5);
        
        for(uint8_t i = 0; i<5; i++)
          {
            NRF_LOG_INFO("Data Received %d 0x%x", i, values[i]);
          }
          nrf_delay_ms(10);

        idle_state_handle();
    }

RE: SPI read and write multiple bytes of varying lengths with MCP2515

hmolesworth — Thu, 12 Sep 2019 18:12:25 GMT

So is this the call:

uint8_t someBuffer[5];
mcp2515_readRegisterS(0, someBuffer, 2+5);

RE: SPI read and write multiple bytes of varying lengths with MCP2515

BendaEng — Thu, 12 Sep 2019 17:51:30 GMT

Ok, I guess what I was thinking in that last code snippet was that regardless of when the instruction "MCP_READ_STATUS" was sent (either right after the MCP_READ or as the only byte sent) the outcome was the same.

/*********************************************************************************************************
** Function name:           mcp2515_readRegisterS
** Descriptions:            read registerS
*********************************************************************************************************/

void mcp2515_readRegisterS(const uint8_t address, uint8_t values[], const uint8_t n)
{
    uint8_t i; 
      
    //uint8_t m_tx_buf[] = {MCP_READ, address};
    uint8_t m_tx_buf[] = {address};
    uint8_t m_rx_buf[n]; 
    uint8_t m_tx_length = sizeof(m_tx_buf);
    uint8_t m_rx_length = sizeof(m_rx_buf);

    memset(m_rx_buf, 0, m_rx_length);
        
    spi_xfer_done = false;

    APP_ERROR_CHECK(nrf_drv_spi_transfer(&can_spi, m_tx_buf, m_tx_length, m_rx_buf, m_rx_length));

     while (!spi_xfer_done)
        {
            __WFE();
        }  
  
    // mcp2515 has auto-increment of address-pointer
    for (i=0; i<n-2 && i<CAN_MAX_CHAR_IN_MESSAGE-2; i++)
    {
      values[i] = m_rx_buf[i+2];
    }
    return; 

}

Yielded:

<info> app: Data Received 0 0x0
<info> app: Data Received 1 0x0
<info> app: Data Received 2 0x0
<info> app: Data Received 3 0x3
<info> app: Data Received 4 0x3
<info> app: Transfer completed.

And,

/*********************************************************************************************************
** Function name:           mcp2515_readRegisterS
** Descriptions:            read registerS
*********************************************************************************************************/

void mcp2515_readRegisterS(const uint8_t address, uint8_t values[], const uint8_t n)
{
    uint8_t i; 
      
    uint8_t m_tx_buf[] = {MCP_READ, address};
    //uint8_t m_tx_buf[] = {address};
    uint8_t m_rx_buf[n]; 
    uint8_t m_tx_length = sizeof(m_tx_buf);
    uint8_t m_rx_length = sizeof(m_rx_buf);

    memset(m_rx_buf, 0, m_rx_length);
        
    spi_xfer_done = false;

    APP_ERROR_CHECK(nrf_drv_spi_transfer(&can_spi, m_tx_buf, m_tx_length, m_rx_buf, m_rx_length));

     while (!spi_xfer_done)
        {
            __WFE();
        }  
  
    // mcp2515 has auto-increment of address-pointer
    for (i=0; i<n-2 && i<CAN_MAX_CHAR_IN_MESSAGE-2; i++)
    {
      values[i] = m_rx_buf[i+2];
    }
    return; 

}

Yielded:

<info> app: Data Received 0 0x0
<info> app: Data Received 1 0x0
<info> app: Data Received 2 0x0
<info> app: Data Received 3 0x3
<info> app: Data Received 4 0x3
<info> app: Transfer completed.

If I send a MCP_READ_STATUS instruction I believe I should be receiving the following (since it outputs the same data each byte read).

<info> app: Data Received 0 0x3
<info> app: Data Received 1 0x3
<info> app: Data Received 2 0x3
<info> app: Data Received 3 0x3
<info> app: Data Received 4 0x3
<info> app: Transfer completed.

It looks like the first three buffer locations of m_rx_buf (i.e. m_rx_buf[2], m_rx_buf[3], and m_rx_buf[4] are getting overwritten, or I'm not looking in the proper location for the received data.

RE: SPI read and write multiple bytes of varying lengths with MCP2515

hmolesworth — Thu, 12 Sep 2019 17:15:47 GMT

That's a step backwards - tx_length must be 2 not 1, as the command byte MCP_READ is not being sent in that latest code snippet; the original m_tx_buf was correct:

    uint8_t m_tx_buf[] = {MCP_READ, address};

RE: SPI read and write multiple bytes of varying lengths with MCP2515

BendaEng — Thu, 12 Sep 2019 16:58:41 GMT

That was part of it, the return was misplaced. When ran the data received is the following (for READ_STATUS):

<info> app: Data Received 0 0x0
<info> app: Data Received 1 0x0
<info> app: Data Received 2 0x0
<info> app: Data Received 3 0x3
<info> app: Data Received 4 0x3
<info> app: Transfer completed.

It seems like the sizeof() is being handled properly. I changed the values to how much I want to read and it doesn't make a difference.

uint8_t m_tx_buf[] = {address};
    uint8_t m_rx_buf[n]; 
    uint8_t m_tx_length = 1; //sizeof(m_tx_buf);
    uint8_t m_rx_length = 5; //sizeof(m_rx_buf);

    memset(m_rx_buf, 0, m_rx_length);
        
    spi_xfer_done = false;

    APP_ERROR_CHECK(nrf_drv_spi_transfer(&can_spi, m_tx_buf, m_tx_length, m_rx_buf, m_rx_length));

     while (!spi_xfer_done)
        {
            __WFE();
        }

Another interesting thing to note: When I change the '2' to '3' in the for loop I get the following output (the 0x10 corresponds to what I received previously:

<info> app: Data Received 0 0x0
<info> app: Data Received 1 0x0
<info> app: Data Received 2 0x10
<info> app: Data Received 3 0x3
<info> app: Data Received 4 0x3
<info> app: Transfer completed.

for (i=0; i<n-3 && i<CAN_MAX_CHAR_IN_MESSAGE-3; i++)
    {
      //values[i] = spi_read();
      values[i] = m_rx_buf[i+3];
    }
    return;

Thanks!

RE: SPI read and write multiple bytes of varying lengths with MCP2515

hmolesworth — Thu, 12 Sep 2019 16:19:01 GMT

I think READ and READ_RX_BUFFER both auto-increment starting at the supplied address, but READ_STATUS does not, it simply repeats the status byte for verification and error checking. I only had time for a quick look, and I see the return statement is misplaced which means you were looking at random data on the stack after the first byte:

Code above:
    for (i=0; i<n-2 && i<CAN_MAX_CHAR_IN_MESSAGE-2; i++)
    {
      return values[i] = m_rx_buf[i+2];
    }
Should be:
    for (i=0; i<n-2 && i<CAN_MAX_CHAR_IN_MESSAGE-2; i++)
    {
      values[i] = m_rx_buf[i+2];
    }
    return;

I assume MCP_READ is 0x03? Also I am not sure all compilers would handle sizeof() correctly when used on a passed parameter but that could be easily verified with a breakpoint