DECDSR DEC Device Status Reports

DEC's private status requests: the extended cursor position, the printer, the keyboard, macro space and the like.

CSI ? Ps n

DEC STD 070: §5.4.4 Extended Cursor Position Report, p. 5-55
VT510: DSR—Device Status Reports

With a ? before the parameter, a device status report asks one of DEC’s own questions. Each has its own answer:

`Ps`	Asks for	xterm, as a VT420, answers
`6`	the cursor position, with the page: DECXCPR	`CSI ? Pl ; Pc ; 1 R`
`15`	the printer’s status	`CSI ? 13 n`, no printer
`25`	whether the user-defined keys are locked	`CSI ? 20 n`, unlocked
`26`	the keyboard	`CSI ? 27 ; 1 ; 0 ; 0 n`: North American, ready, an LK201
`55`	the locator’s status	`CSI ? 53 n`, no locator
`56`	the locator’s type	`CSI ? 57 ; 0 n`, unknown
`62`	the space left for macros: DECMSR	`CSI 0000 * {`, none
`63 ; Pid`	a checksum of the macros: DECCKSR	`DCS Pid ! ~ 0000 ST`
`75`	the data integrity flag	`CSI ? 70 n`, no errors
`85`	the multiple-session configuration	`CSI ? 83 n`, not configured

These are the answers in xterm’s CASE_DSR, from a default build, which is a VT420 (DFT_DECID). Each is gated on a terminal level: the printer, keyboard and user-defined key reports need a VT220 or later, the locator reports a VT330, and DECMSR, DECCKSR, data integrity and multiple sessions a VT420. The locator answers depend on how xterm was built: with --enable-dec-locator, which is off by default, it answers CSI ? 50 n (ready) and CSI ? 57 ; 1 n (a mouse) instead. xterm also answers CSI ? 5 n with CSI ? 0 n, the operating status in the private form.

DECXCPR is the cursor position report with the page number added. DEC STD 070 makes it a level 3 and 4 function, and counts the line and column from the margins in origin mode, as CPR does. Its answer starts CSI ?; the VT510 manual’s DECXCPR page leaves the ? out, but xterm sends it, and esctest2’s test_DECDSR_DECXCPR expects it. xterm, with one page, always reports page 1.

DECMSR reports the bytes free for macros, divided by 16 (DEC STD 070 §5.12.3, p. 5-185). xterm has no macros and reports none; it writes the number as four hexadecimal digits, 0000, where DEC STD 070 defines a plain number.

DECCKSR reports a checksum as four hexadecimal digits in a control string labelled with the Pid the request gave (DEC STD 070 §5.12.2, p. 5-181). The same report answers DECRQCRA’s checksum of a rectangle. With no macros, xterm reports 0000.

The VT510 manual describes the others on their own pages: printer port, user-defined keys, keyboard, macro space, memory checksum and data integrity.

Not in libghostty-vt

libghostty-vt answers none of these. Its DSR dispatch in stream.zig looks the request up in a table, entries in device_status.zig, that has only the ANSI requests 5 and 6 and two private ones of its own, ?996 (the color scheme) and ?998 (visibility); any other request, and any with two parameters such as ?63 ; Pid, is logged as invalid and dropped. Every case below that expects an answer is therefore a known difference: xterm, a VT420 by default, sends it.

Validation

DECDSR-1: Extended cursor position

\e[2;3H
\e[?6n

|_____|
|_____|
|_____|
reply \e[?2;3;1R

DECDSR-2: Counted from the margins in origin mode

\e[?69h   # allow left and right margins
\e[2;5s   # margins at columns 2 and 5
\e[2;4r   # region is lines 2 to 4
\e[?6h    # origin mode
\e[2;2H   # line 3, column 3 of the screen
\e[?6n

|_____|
|_____|
|_____|
|_____|
cursor 3,3
reply \e[?2;2;1R

DECDSR-3: Operating status, the private way

\e[?5n

|_____|
reply \e[?0n

DECDSR-4: Printer, user-defined keys and keyboard

\e[?15n   # printer
\e[?25n   # user-defined keys
\e[?26n   # keyboard

|_____|
reply \e[?13n\e[?20n\e[?27;1;0;0n

DECDSR-5: The locator

\e[?55n   # status
\e[?56n   # type

|_____|
reply \e[?53n\e[?57;0n

DECDSR-6: Macro space

\e[?62n

|_____|
reply \e[0000*{

DECDSR-7: Memory checksum

\e[?63;123n

|_____|
reply \eP123!~0000\e\\

DECDSR-8: Data integrity and multiple sessions

\e[?75n   # data integrity
\e[?85n   # multiple sessions

|_____|
reply \e[?70n\e[?83n

DECDSR-9: A request it does not know

\e[?99n

|_____|
reply none