HECC_MAX_MAILBOXES
mbxno = HECC_MAX_MAILBOXES - 1 - cnt;
#define HECC_MAX_RX_MBOX (HECC_MAX_MAILBOXES - HECC_MAX_TX_MBOX)
#define HECC_RX_FIRST_MBOX (HECC_MAX_MAILBOXES - 1)