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Merge #19420

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19420: cpu/esp32: use ets_printf instead of puts in startup r=maribu a=gschorcht

### Contribution description

This PR provides a workaround that fixes the problem that restarting an application automatically after flashing it in download mode via USB Serial/JTAG doesn't work and requires a hard reset by pressing the RESET button before it starts.

The reason that the application doesn't restart automatically after flashing it is that an exception occurs if `puts` or `printf` is called during startup before the first interrupt driven context switch in `thread_yield_higher`. The console seems to hange after bootloader:
```
EESP-ROM:esp32c3-api1-20210207
Build:Feb  7 2021
rst:0x15 (USB_UART_CHIP_RESET),boot:0xd (SPI_FAST_FLASH_BOOT)
Saved PC:0x40380786
SPIWP:0xee
mode:DIO, clock div:1
load:0x3fcd6100,len:0x6c
load:0x403ce000,len:0x7ec
load:0x403d0000,len:0x2170
entry 0x403ce000
Pro cpu up.
```
However, the system stucks in a exception/printf loop. ESP32-C3 and ESP32-S3 are affected.

### Testing procedure

Flash a ESP32-C3 or ESP32-S3 board that don't have a USB-to-UART chip with reset logic on board, for example
```
BOARD=hip-badge make -j8 -C tests/shell flash
```
or
```
BOARD=esp32s3-pros3 make -j8 -C tests/shell flash
```
Connect a terminal to the the board. Without the PR, the console doesn't seem to work and the RESET button has to pressed explicitly to get it working. With the PR, the console should work.

The problem can also be caused when using
```
dist/tools/esptools/espreset.py -p /dev/ttyACM0
```
while connected with a terminal to the board. Without the PR, the console output stops after
```
ESP-ROM:esp32c3-api1-20210207
Build:Feb  7 2021
rst:0x15 (USB_UART_CHIP_RESET),boot:0xd (SPI_FAST_FLASH_BOOT)
Saved PC:0x40380786
SPIWP:0xee
mode:DIO, clock div:1
load:0x3fcd6100,len:0x6c
load:0x403ce000,len:0x7ec
load:0x403d0000,len:0x2170
entry 0x403ce000
Pro cpu up.
```
while it continues with the PR as following:
```
main(): This is RIOT! (Version: 2023.04-devel-713-gcb721-boards/
test_shell.
>
```

### Issues/PRs references



Co-authored-by: Gunar Schorcht <gunar@schorcht.net>
This commit is contained in:
bors[bot] 2023-03-24 19:00:42 +00:00 committed by GitHub
commit 71e5b2cb5e
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1 changed files with 1 additions and 1 deletions
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2
cpu/esp32/startup.c
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@ -322,7 +322,7 @@ static NORETURN void IRAM system_init (void)
LOG_STARTUP("Starting RIOT kernel on PRO cpu\n");
esp_rom_uart_tx_wait_idle(CONFIG_ESP_CONSOLE_UART_NUM);
#else
puts("");
ets_printf("\n");
#endif
kernel_init();
UNREACHABLE();