At work I make heavy use of the GNU Emacs mode serial-term<\/i> to interface with various target boards. The boards all run U-Boot with a 5 second autoboot timeout. I often want to power-cycle a group of boards, then stop them all at the U-Boot prompt before they autoboot. It’s a race to C-x b<\/i> to all the different buffers in time. I used to frequently miss some buffers; the boards would start booting, and I would have to wait to issue a software reset. It became annoying enough that I decided to create an autostop extension. <\/p>\n
Luckily, serial-term<\/i> is written in Emacs Lisp, so I can extend it to do exactly what I want. In this case I want a global “U-Boot autoboot-stop” mode. Here’s what I came up with: <\/p>\n
First, a variable to to keep track of whether the mode is enabled or not. <\/p>\n
;; <\/span>Detect U-Boot autoboot prompt and stop it.<\/span>\r\n(defvar<\/span> u-boot-stop-autoboot-mode<\/span> nil\r\n \"Non-nil if term-mode should prevent U-Boot from autobooting.<\/span>\r\nUse the function u-boot-toggle-stop-autoboot-mode to toggle.\"<\/span>)\r\n<\/pre>\n Then the advice itself. It jacks into the term-emulate-terminal<\/i> process filter to detect the U-Boot autoboot prompt, then sends a newline in response. <\/p>\n(defadvice<\/span> term-emulate-terminal<\/span>\r\n (before u-boot-maybe-stop-autoboot activate disable)\r\n (with-current-buffer<\/span> (process-buffer proc)\r\n (when<\/span> (string-match \"Hit any key to stop autoboot:\"<\/span> str)\r\n (message \"U-Boot autoboot stopped in buffer %s\"<\/span>\r\n (buffer-name (current-buffer)))\r\n (term-send-raw-string \"\\n\"<\/span>))))\r\n<\/pre>\n And finally a function to toggle the advice on and off. <\/p>\n
(defun<\/span> u-boot-toggle-stop-autoboot-mode<\/span> ()\r\n \"Toggle whether or not term-mode should interrupt U-Boot autoboot.\"<\/span>\r\n (interactive)\r\n (if<\/span> u-boot-stop-autoboot-mode\r\n (progn<\/span>\r\n (ad-disable-advice\r\n 'term-emulate-terminal 'before 'u-boot-maybe-stop-autoboot)\r\n (ad-update 'term-emulate-terminal)\r\n (setq u-boot-stop-autoboot-mode nil)\r\n (message \"U-Boot autoboot will not be interrupted\"<\/span>))\r\n (progn<\/span>\r\n (ad-enable-advice\r\n 'term-emulate-terminal 'before 'u-boot-maybe-stop-autoboot)\r\n (ad-activate 'term-emulate-terminal)\r\n (setq u-boot-stop-autoboot-mode t)\r\n (message \"U-Boot autoboot will be interrupted\"<\/span>))))\r\n<\/pre>\n Now I can enable the mode globally with <\/p>\n
M-x u-boot-toggle-stop-autoboot-mode<\/i> <\/p>\n
and be sure that all the boards will be interrupted in time. <\/p>\n
It’s worth noting that developing this feature was relatively straightforward. I never left my Emacs session; I developed the code right in ~\/.emacs.d\/init.el<\/code>, tested it quickly in a terminal<\/i> buffer, and confirmed its operation in my existing serial-term<\/i> buffers. Most of the development time was spent reading the Info<\/i> documentation for Advice, to figure out how to enable and disable a specific piece of advice. <\/p>\n","protected":false},"excerpt":{"rendered":"At work I make heavy use of the GNU Emacs mode serial-term to interface with various target boards. The boards all run U-Boot with a 5 second autoboot timeout. I often want to power-cycle a group of boards, then stop them all at the U-Boot prompt before they autoboot. It’s a race to C-x b … <\/p>\n