iprintln!(), itm::write_all(), etc not compatible with STM32CubeIDE Serial Wire Viewer (should send on char per u32)

[banyanshade-software]

Good evening !
I'm starting to use rust+cortex-m on STM32, and I'm planning to mix existing C code (using STM32CubeIDE, CMSIS and freeRTOS) and Rust code (as a static library).
In my early experiments, I have trouble with ITM support, which seems incompatible with Cube IDE (or at least the SWV ITM Data console)

itm::write_all(), which is used by write_str() and iprintln!, will send 32bits words on ITM (thus 4 chars per word).
This is not compatible with ST CubeIDE ITM display, and CMSIS Core Peripheral Access Layer

E.g in core_cm4.h: (Drivers/CMSIS/, (provided by ARM I think))

__STATIC_INLINE uint32_t ITM_SendChar (uint32_t ch)
{
  if (((ITM->TCR & ITM_TCR_ITMENA_Msk) != 0UL) &&      /* ITM enabled */
      ((ITM->TER & 1UL               ) != 0UL)   )     /* ITM Port #0 enabled */
  {
    while (ITM->PORT[0U].u32 == 0UL)
    {
      __NOP();
    }
    ITM->PORT[0U].u8 = (uint8_t)ch;
  }
  return (ch);
}

thus a single byte is sent at a time (wasting 75% bandwidth with ascii)

With Rust/Cortex-m:

	itm::write_all(itm(), "DEF".as_bytes());
	itm::write_all(itm(), "DEF".as_bytes());
	itm::write_all(itm(), "DEF".as_bytes());
	itm::write_all(itm(), "\n".as_bytes());

And this will display "D䙅D䙅D䙅" in cube IDE

Trace log shows

hence the D (68), while EF becomes 0x4645 and is displayed as U+4645 character (as if it was utf-32)

IMHO, a mode that complies/mimic with CMSIS lib should be provided (and probably should be default)