fix: prevent UART FIFO overflow during I2C bulk write

[rahul31124]

Fixes #206

Large UART transfers could overflow the 4-byte UART FIFO because the host sends data faster than the I2C bus can transmit it, causing dropped bytes and client timeouts.

Changes

• Added a 255-byte RAM buffer to I2C_CommandWriteBulk.
• Buffer the entire UART payload before starting the I2C transfer.
• Prevent UART FIFO overflows and dropped bytes during large transfers.

Summary by Sourcery

Improve I2C bulk write handling by buffering incoming UART data and integrating watchdog servicing to ensure reliable large-transfer operation.

New Features:

• Buffer UART bulk-write payload in RAM before starting I2C transmission to support larger transfers without data loss.

Bug Fixes:

• Prevent UART FIFO overflow and dropped bytes during large I2C bulk writes by decoupling UART reception from I2C transmission.

Enhancements:

• Add watchdog timer clears during UART buffering and I2C transmission to avoid unintended resets during long bulk writes.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Buffers UART payload into RAM before starting the I2C bulk write and adds watchdog servicing to prevent UART FIFO overflow and timeouts during large transfers.

Sequence diagram for buffered UART to I2C bulk write

sequenceDiagram
    actor Host
    participant UART1
    participant I2C_CommandWriteBulk
    participant I2C_bus
    participant Watchdog

    Host ->> UART1: send device, count, payload bytes
    UART1 ->> I2C_CommandWriteBulk: UART1_Read (device)
    UART1 ->> I2C_CommandWriteBulk: UART1_Read (count)

    loop count bytes
        UART1 ->> I2C_CommandWriteBulk: UART1_Read (payload byte)
        I2C_CommandWriteBulk ->> I2C_CommandWriteBulk: store in usb_buffer
        I2C_CommandWriteBulk ->> Watchdog: WATCHDOG_TimerClear
    end

    I2C_CommandWriteBulk ->> I2C_bus: I2C_StartSignal
    I2C_CommandWriteBulk ->> I2C_bus: I2C_Transmit (device << 1)

    loop count bytes
        I2C_CommandWriteBulk ->> I2C_bus: I2C_Transmit (usb_buffer[i])
        I2C_CommandWriteBulk ->> Watchdog: WATCHDOG_TimerClear
    end

    I2C_CommandWriteBulk ->> I2C_bus: I2C_StopSignal

Loading

File-Level Changes

Change	Details	Files
Buffer incoming UART data into a RAM array before performing the I2C bulk write, and service the watchdog during both UART reception and I2C transmission.	Introduce a static 255-byte buffer used by I2C_CommandWriteBulk to store the entire UART payload before I2C transmission. Refactor I2C_CommandWriteBulk to first read device and count, then copy count bytes from UART into the buffer in a pre-transfer loop. Update the transmission loop to send bytes from the RAM buffer over I2C instead of reading directly from UART. Call the watchdog clear function regularly in both the UART read loop and the I2C transmit loop to avoid watchdog resets during long transfers.	src/bus/i2c/i2c.c

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#206	Decouple UART reception from I2C transmission in I2C_CommandWriteBulk by buffering the entire incoming payload before starting the I2C transfer (up to the 255-byte protocol limit).	✅
#206	Prevent UART FIFO overflow and resulting data corruption/timeouts during large I2C bulk writes.	✅

Possibly linked issues

• I2C_CommandWriteBulk data corruption due to UART FIFO overflow during large transfers #206: PR implements UART payload buffering in I2C_CommandWriteBulk, preventing FIFO overflow and fixing the reported corruption/timeouts.

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[sourcery-ai]

Hey - I've reviewed your changes and they look great!

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[CloudyPadmal]

maybe payload[255]?

[CloudyPadmal]

Do we need to clear the WDT regularly?

[CloudyPadmal]

Same here?

[CloudyPadmal]

Looks good with minor comments.