Standalone USRP2 firmware app is not transmitting

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();

Hey,

I solved it by my own. After increasing the value of scale_i and scale_q
(e.g. 20000) I was able to transmit something.

Hey list,

After verifying the transmitted signal with an spectrum analyzer, it
turns out to be not the expected signal.

The values of the variable “sample” has no effect on the transmission. I
tried to set the value to zero, 10, 100 or even a series of
1,0,1,0,1,0,… without any effect.

So, now I have some questions:

Do I have to setup some settings how to interpret the samples in the
buffer?

Or did I miss another important point?

Can you help me???
Thanks in advance,
Dimitri

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