Flash downloads appears to succeed, but no AT response

[jlthompson]

U believe I faithfully followed the flash download procedure in

ESP32-AT User Guide
Release v2.3.0.0-esp32c3-1067-ge0acd9b0c7
Espressif Systems
May 13, 2025

But I get no response from either the USB or the UART interfaces. See what I have in the attached screenshot.

I tried the factory image by itself, as well as the files in the download.config file. See the attached log file.

What did I do wrong or what am I missing?

[esp-at]

Hello jlthompson,

from the logs you provided, it seems the firmware had downloaded well, but the problem should be on the UART RX side. Could you please check the items according to https://docs.espressif.com/projects/esp ... ml#at-logs.

Search:

Code: Select all

at-common: write dlen:0

~

[jlthompson]

Apologies for the delayed response; I got sidetracked with writing firmware for other system components so that I could make progress.

I am not at all sure what is happening, or even what is supposed to happen, so let me describe some experiments I conducted. For all of these, the ESP32-C6 still has the ESP32-C6-4MB-AT-V4.1.0.0 factory image I programmed it with.

I connect the DevKit-C1 UART port to my PC and open it enumerates as Silicon Labs CP210x USB to UART Bridge (COM4). I launch Tera Term 5, configure it for 115200 baud, 8 data bits, no parity, 1 stop bit, and no flow control. I have the Terminal set to transmit CRLF New-Line. I then connect to COM 4 and immediately get the following:

ESP-ROM:esp32c6-20220919
Build:Sep 19 2022
rst:0x1 (POWERON),boot:0xc (SPI_FAST_FLASH_BOOT)
SPIWP:0xee
mode:DIO, clock div:2
load:0x40875720,len:0x16b8
load:0x4086c110,len:0xe70
load:0x4086e610,len:0x30e8
entry 0x4086c11a
I (23) boot: ESP-IDF v5.4.1-643-g8ad0d3d8f2-dirty 2nd stage bootloader
I (24) boot: compile time Jul 18 2025 10:02:38
I (24) boot: chip revision: v0.2
I (25) boot: efuse block revision: v0.3
I (29) boot.esp32c6: SPI Speed : 80MHz
I (33) boot.esp32c6: SPI Mode : DIO
I (37) boot.esp32c6: SPI Flash Size : 4MB
I (40) boot: Enabling RNG early entropy source...
I (45) boot: Partition Table:
I (47) boot: ## Label Usage Type ST Offset Length
I (54) boot: 0 otadata OTA data 01 00 0000d000 00002000
I (60) boot: 1 phy_init RF data 01 01 0000f000 00001000
I (67) boot: 2 nvs WiFi data 01 02 00010000 0000e000
I (73) boot: 3 at_customize unknown 40 00 0001e000 00042000
I (80) boot: 4 ota_0 OTA app 00 10 00060000 001d0000
I (86) boot: 5 ota_1 OTA app 00 11 00230000 001d0000
I (93) boot: End of partition table
I (96) esp_image: segment 0: paddr=00060020 vaddr=42170020 size=2be00h (179712) map
I (137) esp_image: segment 1: paddr=0008be28 vaddr=40800000 size=041f0h ( 16880) load
I (141) esp_image: segment 2: paddr=00090020 vaddr=42000020 size=1644ach (1459372) map
I (411) esp_image: segment 3: paddr=001f44d4 vaddr=408041f0 size=1c664h (116324) load
I (436) esp_image: segment 4: paddr=00210b40 vaddr=40820860 size=04558h ( 17752) load
I (440) esp_image: segment 5: paddr=002150a0 vaddr=50000000 size=0007ch ( 124) load
I (448) boot: Loaded app from partition at offset 0x60000
I (449) boot: Disabling RNG early entropy source...
I (946) at-init: at param mode: 1
I (1033) at-uart: AT cmd port:uart1 tx:7 rx:6 cts:5 rts:4 baudrate:115200
I (1034) at-init: module_name: ESP32C6-4MB
I (1035) at-init: max tx power=78, ret=0
I (1037) at-init: v4.1.0.0 (gitlab)

I try entering AT+GMR, but nothing changes in the terminal window. There is no character echo, and the UART appears to be unresponsive.

I then disconnect from COM 4 and unplug the cable to the DevKit-1C UART port. I now connect the kit's USB port to my PC. It enumerates as USB Serial Device (COM3).

At first, COM3 appears to be dead — no output and no response. I turn off the PC's USB port and Tera Term indicates that it is now disconnected. But when I turn the USB port back on, it outputs the following:

I (416) esp_image: segment 3: paddr=001f44d4 vaddr=408041f0 sizeI (956) at-init: at param mode: 1
I (1041) at-uart: AT cmd port:uart1 tx:7 rx:6 cts:5 rts:4 baudrate:115200
I (1042) at-init: module_name: ESP32C6-4MB
I (1043) at-init: max tx power=78, ret=0
I (1045) at-init: v4.1.0.0 (gitlab)
W (1202) at-common: write dlen:0

It then seems unresponsive.

Finally, I disconnected the DevKit from the PC, attached a 5 V power supply to J1 pin 14 (5V), and to J1 pin 15 (G). I also attached an FTDI Chip TTL-232RG-VIP-WE cable from my PC to the DevKit J1 pin 1 (3V3), J3 pin 1 (G), J3 pin 2 (TX), and J3 pin 3 (RX).

The FTDI cable enumerated as USB Serial Port (COM6). I launched Tera Term 5, configured it for 115200 baud, 8 data bits, no parity, 1 stop bit, no flow control, and then opened port COM6. On applying power to the DevKit, it outputs the following:

ESP-ROM:esp32c6-20220919
Build:Sep 19 2022
rst:0x1 (POWERON),boot:0xc (SPI_FAST_FLASH_BOOT)
SPIWP:0xee
mode:DIO, clock div:2
load:0x40875720,len:0x16b8
load:0x4086c110,len:0xe70
load:0x4086e610,len:0x30e8
entry 0x4086c11a
I (23) boot: ESP-IDF v5.4.1-643-g8ad0d3d8f2-dirty 2nd stage bootloader
I (24) boot: compile time Jul 18 2025 10:02:38
I (24) boot: chip revision: v0.2
I (25) boot: efuse block revision: v0.3
I (29) boot.esp32c6: SPI Speed : 80MHz
I (33) boot.esp32c6: SPI Mode : DIO
I (37) boot.esp32c6: SPI Flash Size : 4MB
I (40) boot: Enabling RNG early entropy source...
I (45) boot: Partition Table:
I (47) boot: ## Label Usage Type ST Offset Length
I (54) boot: 0 otadata OTA data 01 00 0000d000 00002000
I (60) boot: 1 phy_init RF data 01 01 0000f000 00001000
I (67) boot: 2 nvs WiFi data 01 02 00010000 0000e000
I (73) boot: 3 at_customize unknown 40 00 0001e000 00042000
I (80) boot: 4 ota_0 OTA app 00 10 00060000 001d0000
I (86) boot: 5 ota_1 OTA app 00 11 00230000 001d0000
I (93) boot: End of partition table
I (96) esp_image: segment 0: paddr=00060020 vaddr=42170020 size=2be00h (179712) map
I (137) esp_image: segment 1: paddr=0008be28 vaddr=40800000 size=041f0h ( 16880) load
I (141) esp_image: segment 2: paddr=00090020 vaddr=42000020 size=1644ach (1459372) map
I (411) esp_image: segment 3: paddr=001f44d4 vaddr=408041f0 size=1c664h (116324) load
I (436) esp_image: segment 4: paddr=00210b40 vaddr=40820860 size=04558h ( 17752) load
I (440) esp_image: segment 5: paddr=002150a0 vaddr=50000000 size=0007ch ( 124) load
I (448) boot: Loaded app from partition at offset 0x60000
I (449) boot: Disabling RNG early entropy source...
I (946) at-init: at param mode: 1
I (1032) at-uart: AT cmd port:uart1 tx:7 rx:6 cts:5 rts:4 baudrate:115200
I (1033) at-init: module_name: ESP32C6-4MB
I (1034) at-init: max tx power=78, ret=0
I (1036) at-init: v4.1.0.0 (gitlab)

After that, I got nothing more, and the port was unresponsive.

I then installed Advanced Serial Port Monitor (https://www.aggsoft.com/serial-port-monitor.htm) to see what it would display. After extensive experimentation, I discovered that the RTS and DTR lines are asserted by default. When either port is connected to a PC using a USB serial cable, it triggers the ESP32 to output the data shown above. Toggling RTS also does the same.

I am now totally at a loss for how to proceed. I have a project with thousands of installations, where I have specified this part for use based on its wide acceptance. I know it should be able to do work, but I can't even talk to it so I can develop the application, even though programming the part went well.

[esp-at]

Hi jlthompson,
It seems that all your attempts are in the wrong direction. You are trying to send and receive AT commands on the AT log port (UART0), which is incorrect.

Please refer to the documentation at https://docs.espressif.com/projects/esp ... 4mb-series.

You should be sending and receiving AT commands on UART1. Kindly refer to the 'ESP32-C6-4MB Series Hardware Connection' section in the link and try again.