Issue#3849 fix backported to 2.9 (#3857)

* Issue#3849 fix backported to 2.9
Fixes calc_ifdelay() for baud > 19200 that was setting bit timing delays incorrectly leading to a variety of communication problems.
Fixes ENOMSG error handling that was locking up modbus communication.

* Back to original voodoo caused by conflating modbus timing calculation with pktuart hardware implementation.
(175u * baudrate + 99999u) / 100000u; could be implemented as (7u * baudrate + 3999(/4000; which would improve the calculation range but doesn't matter because already screening out large baud rates.

* Fix msg and reverse (baudrate > 19200).

---------

Co-authored-by: JTrantow <jerry.trantow@cumuluspd.com>

Author: JTrantow

src/hal/drivers/mesa-hostmot2/hm2_modbus.c

@@ -387,10 +387,10 @@ static unsigned calc_ifdelay(hm2_modbus_inst_t *inst, unsigned baudrate, unsigne
 	}
 
 	// calculation works for baudrates less than ~24 Mbit/s
-	if(baudrate <= 19200)
+	if(baudrate > 19200)
 		return (175u * baudrate + 99999u) / 100000u;
 	unsigned bits = 1 + 8 + (parity ? 1 : 0) + (stopbits > 1 ? 2 : 1);
-	return (bits * 35 + 9) / 10;	// Bit-times * 3.5 rounded up
+	return (bits * 35 + 9) / 10;	// Ceil of bits in 3.5 characters.
 }
 
 //
@@ -1049,12 +1049,10 @@ static void process(void *arg, long period)
 			break;
 		}
 		if(inst->maxicharbits && HM2_PKTUART_RCR_ICHARBITS_VAL(frsize) > inst->maxicharbits) {
-			MSG_WARN("%s: warning: reply to command %u had too long inter-character delay (%u > %u), dropping\n",
+			MSG_WARN("%s: warning: reply to command %u had too long inter-character delay (%u > %u), trying to interpret\n",
 					inst->name, inst->cmdidx,
 					HM2_PKTUART_RCR_ICHARBITS_VAL(frsize), inst->maxicharbits);
 			set_error(inst, ENOMSG);
-			force_resend(inst);
-			break;
 		}
 		inst->rxdata[0] = 0;	// This will fail the parse packet if the read did not resolve
 		r = hm2_pktuart_queue_read_data(inst->uart, inst->rxdata, HM2_PKTUART_RCR_NBYTES_VAL(frsize));