Function CmdExchange 

#[unsafe(no_mangle)]
pub extern "C" fn CmdExchange(
    requestJSON: *mut c_char,
    responseJSON: *mut c_char,
    maxResponseLen: i32,
) -> i32

Blocking call to send out request and wait for response from R/W with 1sec timeout

Parameters

• requestJSON: Request to R/W in JSON format
• responseJSON: Buffer to store response from R/W in JSON format
• maxResponseLen: Size of responseJSON buffer (minimum size is 4096 bytes)

Returns

• 0: Message send/receive succeeded
• -1: COM not opened
• -2: Communication error with R/W
• -3: responseJSON buffer size not enough
• -6: Link busy

Safety

The caller must ensure:

• requestJSON points to a valid null-terminated string
• responseJSON points to a writable buffer of at least maxResponseLen bytes
• maxResponseLen is positive and represents the actual buffer size (minimum 4096)