Wrong baud rate on ESP32-S3 stock SoC

[rmedaer]

Hi there,

I build a product using a ESP32-S3. After multiple tests and POCs using development boards, it's now time to build a custom PCB.
Before PCB fab, I first test my schematics on breadboard with QFN56 socket. Everything seems to look good except that I have strange behavior with the chip:

1. I'm not able to use embedded USB-to-serial. Looking at the USB bit and bytes, it looks like the chip doesn't answer to USB address request.
2. Therefore I plugged an external USB-to-serial IC in order to use UART port.
3. Great news, it works... but not with 115200 bps ! In boot mode IO0 to low, I receive the following message at 38400 bps (measured with an analyzer) !!! Why ?

Code: Select all

ESP-ROM:esp32s3-20210327
Build:Mar 27 2021
rst:0x1 (POWERON),boot:0x0 (DOWNLOAD(USB/UART0))
waiting for download

4. I'm not able to read chip id. But it reads MAC address...

Code: Select all

Serial port /dev/ttyACM1
Connecting....
Chip is ESP32-S3 (QFN56) (revision v0.1)
Features: WiFi, BLE
Crystal is 40MHz
MAC: f4:12:fa:ef:bb:4c
Enabling default SPI flash mode...
WARNING: Failed to communicate with the flash chip, read/write operations will fail. Try checking the chip connections or removing any other hardware connected to IOs.
Warning: ESP32-S3 has no Chip ID. Reading MAC instead.
MAC: f4:12:fa:ef:bb:4c
Hard resetting via RTS pin...

5. Last but not least, I'm not able to read Flash ID but I can see with the analyzer that the flash responds well on SPI bus.


Do I missed something on chip initialization to fix the following ?

- USB
- UART baud rate
- Chip ID
- Flash

Many thanks in advance,

[ESP_Sprite]

In general: If you value your sanity, do not use a breadboard for anything high-frequency (with 'high frequency' being anything above like a megahertz or something). In this particular case, your breadboard probably has all sorts of parasitic capacitance/inductance issues leading the crystal to oscillate at a wrong frequency; the SPI lines likely are also affected by that. As a rule, you cannot test a bare ESP32 chip in a breadboard; you must build a PCB that adheres to the hardware design guidelines to have a properly working chip. (For completeness: it's OK to plug a devkit or module into a devboard, as with those the high-frequency stuff is 'contained' and doesn't rely on the breadboard).