DSR Device Status Report

A host sends DSR to ask the terminal something, and the terminal answers by sending a sequence back. Ps says what is asked:

The answers 0 and 3 are themselves DSRs, sent the other way. A terminal that receives one has not been asked anything, and does not answer.

The cursor position report is CPR, defined in ECMA-48 §8.3.14 as Active Position Report, p. 35, in DEC STD 070 §5.4.4, p. 5-53, and in the VT510 manual as DSR—Cursor Position Report. Pl is the line and Pc the column, counting from 1. With origin mode on, DEC STD 070 counts them from the top and left margins instead, the same way CUP counts the position it is given, so a host can send a report straight back as a CUP.

DEC STD 070 sends its reports with the 8-bit CSI, 9B. libghostty-vt sends ESC [, as a terminal sending only 7-bit controls does.

DEC terminals answer many more Ps values, for the printer, the keyboard, and with a ? before the parameter (CSI ? 6 n is DECXCPR, the cursor position with the page number). libghostty-vt answers 5 and 6 only.

Validation

DSR-1: Operating status

\e[5n

|_____|
reply \e[0n

DSR-2: Cursor position

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

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

DSR-3: 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;2R

DSR-4: With a wrap pending

ABCDE     # fills the line; a wrap is pending
\e[6n

|ABCDE|
|_____|
reply \e[1;5R

DSR-5: A report is not a question

\e[0n     # "ready", as a terminal would answer
\e[3n     # "not working"

|_____|
reply none