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Fully detach USART2 from MCSDK ASPEP/DMA before CLI mode #1

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Fully detach USART2 from MCSDK ASPEP/DMA before CLI mode #1

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29 changes: 28 additions & 1 deletion fmc/Src/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,7 @@
#include "fmac_rt.h"
#include "cli.h"
#include "stm32g4xx_ll_usart.h"
#include "stm32g4xx_ll_dma.h"
/* USER CODE END Includes */

/* Private typedef -----------------------------------------------------------*/
Expand Down Expand Up @@ -108,12 +109,38 @@ int main(void)
/* Initialize interrupts */
MX_NVIC_Init();
/* USER CODE BEGIN 2 */

/*── Fully detach USART2 from the MCSDK ASPEP / DMA path ──────────────
*
* MX_MotorControl_Init() → ASPEP_start() enables DMA requests (DMAR,
* DMAT), DMA channels, and several USART interrupts for the ASPEP
* protocol. We must undo ALL of them before entering CLI polling mode,
* otherwise the ASPEP state-machine (still ticked by SysTick /
* TIM1_BRK) can fire spurious DMA transmissions whose bytes appear
* as garbled output on the serial terminal.
*/

/* 1. Disable DMA requests so USART2 stops feeding/draining DMA. */
LL_USART_DisableDMAReq_RX(USART2);
/* CLI uses USART2 in polling mode; keep MCSDK ASPEP IRQ path fully disabled. */
LL_USART_DisableDMAReq_TX(USART2);

/* 2. Disable the DMA channels that ASPEP_start() enabled. */
LL_DMA_DisableChannel(DMA1, LL_DMA_CHANNEL_1); /* USART2_RX */
LL_DMA_DisableChannel(DMA1, LL_DMA_CHANNEL_2); /* USART2_TX */

/* 3. Disable all USART2 interrupt sources used by ASPEP. */
LL_USART_DisableIT_TC(USART2);
LL_USART_DisableIT_IDLE(USART2);
LL_USART_DisableIT_ERROR(USART2);
HAL_NVIC_DisableIRQ(USART2_IRQn);

/* 4. Clear every pending USART2 flag (ORE, FE, NE, IDLE, TC …)
* and flush any stale byte out of RDR so the first real received
* byte is clean. */
USART2->ICR = USART_ICR_PECF | USART_ICR_FECF | USART_ICR_NECF
| USART_ICR_ORECF | USART_ICR_IDLECF | USART_ICR_TCCF
| USART_ICR_CMCF;
(void)USART2->RDR; /* read-and-discard clears RXNE */
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@chatgpt-codex-connector chatgpt-codex-connector Bot Feb 24, 2026

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P2 Badge Avoid unconditional RDR flush before CLI starts

The new unconditional USART2->RDR read drops one received byte every boot, so if a host/script sends data immediately after reset (before entering the polling loop), the first CLI character is silently lost and commands can be malformed. This is user-visible in automated bring-up flows and can be avoided by only draining RDR when a stale/error condition is actually present (e.g., gated on RXNE/error flags).

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fmac_rt_init();
cli_init();
/* USER CODE END 2 */
Expand Down