07828: coco, coco2, coco2b, coco3: Printing to the 4 pin serial port not working.

ID	Category [?]	Severity [?]	Reproducibility	Date Submitted	Last Update
07828	Core	Minor	Always	Dec 24, 2020, 02:51	Sep 2, 2021, 03:43

Tester	star2root	View Status	Public	Platform	MAME (Self-compiled)
Assigned To	tlindner	Resolution	Fixed	OS	MacOS X
Status [?]	Resolved			Driver	trs/coco12.cpp
Version	0.224	Fixed in Version	0.229	Build	64-bit
		Fixed in Git Commit	4214093	Github Pull Request #	#7652

Summary	07828: coco, coco2, coco2b, coco3: Printing to the 4 pin serial port not working.
Description	Any attempt to print to the bit banger port fails. OS9/NitrOS9 gives error 246, device not ready. BASIC simply hangs.
Steps To Reproduce	Setup a printout file, type in a short BASIC program and type: LLIST
Additional Information	It seems that the input line (FF22 bit 0) is getting enabled to indicate that the printer is offline. This functionality was working some where around version 0.199.
Github Commit

Flags	Verified with Original
Regression Version	0.199
Affected Sets / Systems	coco, coco2, coco2b, coco3

Attached Files

No.18286 star2root Viewer Dec 24, 2020, 19:49 edited on: Dec 24, 2020, 20:37	I removed the code in the OS9 scbbp bit banger printer device driver that checks for the input signal and was able to print, so the problem is definitely that the serial 4 pin input is being set in MAME. Suffice to say, the original OS9 code woks fine on a real CoCo without removing the input pin check.
No.18287 star2root Viewer Dec 24, 2020, 20:41	Notes on the CoCo 4 pin serial port: Note that pins of connector are not always used the same way! This is possible because most everything is done in software; pins 1 and 2 are required by the hardware to be inputs, but it is up to the program to decide how to use those inputs. While any sort of communications program should use the RS-232 pin-out, the built-in BASIC printer routines use pin 2 (RS232 input) as "printer status" and completely ignores pin 1. So the cable you wire up for a printer has to be different from the one you wire up for a modem.
No.18288 star2root Viewer Dec 24, 2020, 22:21	On my real CoCo 3, PRINT HEX$(PEEK(&HFF22)) returns a 4, bit 0 is clear, and LLIST does not hang. On MAME, PRINT HEX$(PEEK(&HFF22)) returns a 5, and LLIST hangs if any BASIC program is present to list.
No.18289 tlindner Moderator Dec 24, 2020, 23:33	Color BASIC requires the RX pin low to print to a printer. OS-9 is the same. All Radio Shack printers did this, so there was never a problem on real hardware. In MAME, the printer image device doesn't do this. I've been meaning to add a configuration for this mode, but have never gotten around to it..
No.18290 star2root Viewer Dec 25, 2020, 06:34	Where and how is the best way to force this line to default to low. I checked my real CoCo 3 (I haven't checked the CoCo 1 yet, but I expect the same behavior) and the input line defaults to low when nothing is connected. If MAME is supposed to emulate the hardware, then the default state of this bit (bit 0, FF22) should be zero.
No.18360 tlindner Moderator Jan 10, 2021, 04:41	I've submitted a PR to emulate this small aspect of Radio Shack printers. https://github.com/mamedev/mame/pull/7652
No.18540 star2root Viewer Mar 14, 2021, 09:16	As of version 0.229, it seems to work under OS-9 or NitrOS9, but while Disk BASIC no longer hangs, the printer output file contains random looking characters.
No.18575 tlindner Moderator Mar 16, 2021, 23:08	I've re-tested with the latest source and verified coco2b with BASIC, and stock OS-9 Level 1. I've also retested with coco3 with BASIC and stock OS-9 Level 2. All is working. MAME was kept at 600 bps at 8-1-N. The problem you describe would also be caused by a mismatch in baud or protocol.
No.18725 tlindner Moderator Apr 20, 2021, 16:58	I nominate this for closure.
No.19198 star2root Viewer Sep 1, 2021, 23:54	I confirm, the patches work, this can be closed.