Using the McBSP in TDM mode on the AM3517 under Linux

Jeremiah

Apologies for not responding sooner.

I'm not a Linux expert but, if you want, I can provide you with some low level examples that show the setup and configuration of the McBSP with multiple DMA for transmit and receive using multiple buffers for each. 

In addition, we'll work on getting more information on the Linux aspect.

  Paul

Paul,

I work with Jeremiah in the same office. Any low level examples you can provide would be very useful at this point. I have familiarity with the kernel files that require modifications for the McBSP on our system.

Thanks,
Tony

Paul,

Thanks for sending the code; I will setup the code in my local kernel and test module to perform the same steps.

Regards,
Tony

Paul,

We were able to get the CodeComposer code running last week modifying it for a TDM configuration,. Yesterday we were able to get a prototype running on the Linux side. Thank you very much for your assistance.

Jeremiah

Jeremiah

Thanks for the feedback, glad I could help.

  Paul

Hello,

where is this zip file?

I have some problem with the mcbsp dma.

Thanks

Ikudo,

I'm unsure where the zip file disappeared to. So, I've attached it to this response.

Thanks,

Tony

7624.MCBSP_RX_DMA_1.zip

Thanks a lot

Jeremiah,

I am interested in using the McBSP ports on a DM3730 under Linux to pull in data from an TI AD1278 ADC. Can you provide some insight or references to how you got your McBSP module working?

Thanks,

Alex.

I first have a question for you, are you doing one off conversions or continuous conversions? Also, on the AD1278, is your data in TDM mode (assuming this) or each channel on its own DOUT pin? The interesting thing is, I am familiar with the AD1274 as I interfaced it to a TI C6748 DSP.

Your biggest challenge will be to correctly obtain and link several DMA channels together to continually stream in the data from the AD1278. On the C6748 I did a ping/pong double buffer. While the ping buffer was being filled with incoming data, I was able to process the pong buffer. When the pong buffer was being filled, I was able to process the ping buffer. Depending on your setup, a double buffer may be adequate, or you may need to go to a triple buffer to ensure no sample loss.

On the C6748, I actually needed three DMA channels configured: Initial, link1 and lilnk2. When it was working, this is how it went:

initial->link1->link2->link1->link2->link1............

This could have just been an issue with the C6748, but I thought I should warn you.

As for the Linux side, the driver I wrote was for the older 2.6.32 kernel. All the omap_ functions are functions provided in the kernel.

void mcbsp_tdm_configure_chained_rx_channels(struct mcbsp_tdm_dev* device,
            int rx_length_bytes,
            int elem_count_per_frame,
            int elem_per_packet)
{
    int ic = 0;
    int err_code = 0;
    int rx_lch = 0;
    int num_frames = 0;

    struct omap_dma_channel_params rx_params;
    memset(&rx_params, 0, sizeof(rx_params));

    //dividing by 4 since we are transmitting 32bit elements
    num_frames = (rx_length_bytes >> 2) / elem_count_per_frame;
    device->rx_buffer_length = rx_length_bytes;

    printk(KERN_ALERT "Setting TDM dma rx params");

    for (ic = 0; ic < RX_NUM_DMA_BUFFERS; ic++)
    {
        printk(KERN_ALERT "Request DMA channel for McBSP RX buffer %d (TDM mode).\n", ic);

        if (omap_request_dma(omap24xx_dma_reqs[device->device][RX_STREAM],
                    "McBSP RX (TDM mode)",
                    mcbsp_tdm_rx_dma_callback,
                    device,
                    &rx_lch))
        {
            printk(KERN_ALERT "Unable to request DMA channel for McBSP RX buffer %d (TDM mode).\n", ic);
            err_code = -EAGAIN;
            break;  // break out of the for loop
        }

        device->rx_lch[ic] = rx_lch;

        omap_set_dma_transfer_params(rx_lch,
                OMAP_DMA_DATA_TYPE_S32,
                elem_count_per_frame, num_frames,
                OMAP_DMA_SYNC_PACKET,
                omap24xx_dma_reqs[device->device][RX_STREAM], OMAP_DMA_SRC_SYNC);

        omap_set_dma_src_params(rx_lch,
                0,
                OMAP_DMA_AMODE_CONSTANT,
                //OMAP34XX_MCBSP5_BASE + OMAP_MCBSP_REG_DRR,
                omap34xx_mcbsp_port[device->device][RX_STREAM],
                0, elem_per_packet);

        omap_set_dma_dest_params(rx_lch,
                0,
                OMAP_DMA_AMODE_POST_INC,
                device->physdst[ic],
                1, 1);
    }

    if (err_code == 0)
    {
        // link DMA channels together - assume MAX_NUM_DMA_BUFFERS > 1
        for (ic = 0; ic < (RX_NUM_DMA_BUFFERS - 1); ic++)
        {
            omap_dma_link_lch(device->rx_lch[ic], device->rx_lch[ic+1]);
        }
        // link last channel to first
        omap_dma_link_lch(device->rx_lch[RX_NUM_DMA_BUFFERS-1], device->rx_lch[0]);
    }
}

Here is the callback function. It places the entire buffer received into a kernel fifo buffer. This is a specific 2.6.32 kernel function, but I believe there are equivalents in newer kernels.

static void mcbsp_tdm_rx_dma_callback(int lch, u16 ch_status, void *data)
{
    struct mcbsp_tdm_dev* device = data;
    unsigned int num_bytes = 0;
    unsigned char* buf_ptr = NULL;
    int ic = 0;
    int found = 0;

//    printk(KERN_ALERT "mcbsp_tdm_rx_dma_callback");

    for (ic = 0; ic < RX_NUM_DMA_BUFFERS; ic++)
    {
        if(lch == device->rx_lch[ic])
        {
            found = 1;
            buf_ptr = device->cpu_dst[ic];
            break;
        }
    }

    if(found == 0)
    {
        printk(KERN_ALERT "Incorrect DMA logical channel %d for RX -- no data copied from McBSP\n", lch);
    }

    if (buf_ptr)
    {
        num_bytes = kfifo_put(device->rx_circular_buffer, buf_ptr, device->rx_buffer_length);
        if (num_bytes != device->rx_buffer_length)
        {
            ///\TODO: need to protect against this in case of lost data packets
//          printk(KERN_ALERT "Fifo push failed. Pushed %d bytes but only %d pushed on", device->rx_buffer_length, num_bytes);
        }
    }
}

I have not done a whole lot with this low level code in over five years, so my memory is a bit rusty. I hope this helps.