Unable to Observe IQ Signals from ATEST1/2 Pins on CC2400

[Qianmoxsn]

Hi Team,

I am using the Ubertooth-One board and attempting to retrieve (or set) IQ samples from the CC2400 chip. I have configured the registers as follows:

• ATESTMOD_PD = 0 [to disable power down]
• ATESTMOD_MODE = 0x2 [to output signals from the VGA]

These configurations should bring the IQ signals to pins ATEST1/2 (as referenced in issue #523). However, I am unable to observe these signals on the oscilloscope.

Could there be an issue with using ubertooth-rx alongside the modified firmware, or might there be another potential cause for this behavior?

---

Steps to Reproduce

1. Modify the firmware bluetooth-rxtx (details below).
2. Upload the modified firmware to the board.
3. Run ubertooth-rx in the terminal.
4. Connect pin ATEST1 or ATEST2 to an oscilloscope.

I added the following lines in the main function to enable the Analog Test Module (ATEST) of the CC2400:

debug_printf("\n\n****UBERTOOTH BOOT****\n%s\n", compile_info);

>>> MODIFIED SECTION
uint16_t reg_val;
// Rewrite PAMTST register
reg_val = cc2400_get(PAMTST);
// Clear bit 11 to 0 -- REF: ATESTMOD_PD, cc2400.p.65
reg_val &= 0xF7FF;
// Set bits [10:8] to 2 -- REF: ATESTMOD_MODE[2:0], cc2400.p.65
reg_val &= ~(0b111 << 8);
reg_val |= (0x2 << 8);
cc2400_set(PAMTST, reg_val);
>>> END OF MODIFIED SECTION

while(1){
...
}

Expected Behavior

I expected to observe the logic signals (high/low voltage) on the oscilloscope.

Actual Behavior

Instead of logic signals, I observed a constant voltage of 0.7V on the oscilloscope, while the terminal successfully outputs some decoded BLE information.

Version Information

• Operating System: Ubuntu 18.04
• Ubertooth tools version (ubertooth-rx -V): libubertooth 1.1 (2020-12-R1)
• libbtbb version: libbtbb 1.0 (2018-06-R1)
• Ubertooth firmware version (ubertooth-util -v): Firmware Version: 2020-12-R1 (API:1.07)

---

Thank you for your support and guidance! Please let me know if any additional details or clarifications are needed.