[Discuss-gnuradio] Standalone USRP2 firmware app is not transmitting

[B. Sc. Dimitri Block]

Hello list,

I'm currently working on a firmware app for USRP2 which aims to send a 
signal in a standalone manner. I'm using the the following function. The 
serial interface returns, that it seems to work by outputting infinity 
"Done"s. But on the spectrum analyzer I didn't see anything, except the 
local oscillator.

Did I set the wrong flags/timestamp?

Do I have to care about the channel variable?

Did I initialize the buffer in the correct way?

============================
#define DSP_TX_BUF_0 4 // cpu -> dsp tx

static void SEND_DATA () {
    putstr("Waiting for the buffer pool.\n");

    while((buffer_pool_status->status & BPS_IDLE(DSP_TX_BUF_0)) == 0)
        ;

    putstr("Buffer pool idles. Filling buffer.\n");

    // fill buffer
    uint32_t *p = buffer_ram(DSP_TX_BUF_0);
    uint32_t i;
    uint32_t sample = (3200 << 16) | 0;

    for (i = 0; i < BP_NLINES; i++) {
        p[i] = sample;
    }


    // 1) 32-bit: word0 (flags, etc)
    p[0] = 0 | U2P_TX_IMMEDIATE | U2P_TX_START_OF_BURST | 
U2P_TX_END_OF_BURST;

    // 2) 32-bit: fpga timestamp (time of tx)
    p[1] = -1;

    putstr("Filled buffer. Start sending\n");

    bp_clear_buf(DSP_TX_BUF_0);

    // first xfer
    bp_send_from_buf(DSP_TX_BUF_0, PORT_DSP, 1, 0, BP_LAST_LINE);

    while(1) {

        // fire it off
        bp_send_from_buf(DSP_TX_BUF_0, PORT_DSP, 1, 0, BP_LAST_LINE);

        // wait for xfer to complete
        while ((buffer_pool_status->status &
                  (BPS_DONE(DSP_TX_BUF_0) | BPS_ERROR(DSP_TX_BUF_0))) 
== 0)
                ;

        putstr("Done.\n");

        bp_clear_buf(DSP_TX_BUF_0);
    }
}
============================


I'm using the USRP2 with the daughterboard RFX2400. The antenna is 
connected to the "TX/RX" connector. The settings concerning frequency, 
interp, ... are set according:

============================
double freq = 2400e6;
unsigned int interpolate = 4;
unsigned int scale_i = 1;
unsigned int scale_q = 1;

struct tune_result result;

printf("\nTune Request:\n");
u2_fxpt_freq_t tune_freq = U2_DOUBLE_TO_FXPT_FREQ(freq);
printf("  freq: %u\n", u2_fxpt_freq_round_to_uint(tune_freq));

bool tune_ok = db_tune(tx_dboard, tune_freq, &result);

int interp = interpolate;

int hb1 = 0;
int hb2 = 0;

if (!(interp & 1)){
hb2 = 1;
interp = interp >> 1;
}

if (!(interp & 1)){
hb1 = 1;
interp = interp >> 1;
}

if (interp < MIN_CIC_INTERP || interp > MAX_CIC_INTERP)
        printf("Variable interp %d out of range",interp);
else {
        dsp_tx_regs->interp_rate = (hb1<<9) | (hb2<<8) | interp;
        printf("Interp: %d, register %d\n", interpolate, (hb1<<9) | 
(hb2<<8) | interp);
}

unsigned int scale_iq = (scale_i << 16) | scale_q;
dsp_tx_regs->scale_iq = scale_iq;

SEND_DATA();
============================