remote_bitbang: Add SWD support

This adds new command characters to make SWD work with the new split
jtag and swd operations of bitbang.

The command characters are as follows:
    O - SWDIO drive 1
    o - SWDIO drive 0
    c - SWDIO read request
    d - SWD write 0 0
    e - SWD write 0 1
    f - SWD write 1 0
    g - SWD write 1 1

Documentation has been updated accordingly. The new commands will be
used by an adapted version of the jtag-openocd applet of the "Glasgow
Debug Tool" (https://github.com/glasgowEmbedded/Glasgow). It has been
tested against an stm32f103 and an at91samd21 target.

contrib/remote/bitbang/remote_bitbang_sysfsgpio.c has also been adapted
to support SWD via the new command set. Some limited testing has been
done using a Raspberry Pi 2 with an stm32f103 and an at91samd21 target
attached.

Change-Id: I8e998a2cb36905142cb16e534483094cd99e8fa7
Signed-off-by: Manuel Wick <manuel@matronix.de>
Signed-off-by: David Ryskalczyk <david.rysk@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6044
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

2 files changed, 31 insertions, 11 deletions

diff --git a/doc/manual/jtag/drivers/remote_bitbang.txt b/doc/manual/jtag/drivers/remote_bitbang.txt
index f394d73..7c8eee2 100644
--- a/doc/manual/jtag/drivers/remote_bitbang.txt
+++ b/doc/manual/jtag/drivers/remote_bitbang.txt
@@ -1,15 +1,19 @@
 /** @remote_bitbangpage OpenOCD Developer's Guide
 
-The remote_bitbang JTAG driver is used to drive JTAG from a remote process. The
-remote_bitbang driver communicates via TCP or UNIX sockets with some remote
-process using an ASCII encoding of the bitbang interface. The remote process
-presumably then drives the JTAG however it pleases. The remote process should
-act as a server, listening for connections from the openocd remote_bitbang
-driver.
+The remote_bitbang JTAG+SWD driver is used to drive JTAG and/or SWD from a
+remote process. The remote_bitbang driver communicates via TCP or UNIX
+sockets with some remote process using an ASCII encoding of the bitbang
+interface. The remote process presumably then drives the JTAG/SWD however
+it pleases. The remote process should act as a server, listening for
+connections from the openocd remote_bitbang driver.
 
 The remote bitbang driver is useful for debugging software running on
 processors which are being simulated.
 
+There also is an implementation of the server-side protocol for the
+Glasgow Debug Tool (https://github.com/glasgowEmbedded/Glasgow) through
+the jtag-openocd applet.
+
 The bitbang interface consists of the following functions.
 
 blink on
@@ -24,11 +28,20 @@ write tck tms tdi
 reset trst srst
 	Set the value of trst, srst.
 
+swdio_drive
+	Set the output enable of the bidirectional swdio (tms) pin
+
+swdio_read
+	Sample the value of swdio (tms).
+
+swd_write
+	Set the value of swclk (tck) and swdio (tms).
+
 An additional function, quit, is added to the remote_bitbang interface to
 indicate there will be no more requests and the connection with the remote
 driver should be closed.
 
-These five functions are encoded in ASCII by assigning a single character to
+These eight functions are encoded in ASCII by assigning a single character to
 each possible request. The assignments are:
 
 	B - Blink on
@@ -47,7 +60,14 @@ each possible request. The assignments are:
 	s - Reset 0 1
 	t - Reset 1 0
 	u - Reset 1 1
+	O - SWDIO drive 1
+	o - SWDIO drive 0
+	c - SWDIO read request
+	d - SWD write 0 0
+	e - SWD write 0 1
+	f - SWD write 1 0
+	g - SWD write 1 1
 
-The read response is encoded in ASCII as either digit 0 or 1.
+The read responses are encoded in ASCII as either digit 0 or 1.
 
  */
diff --git a/doc/openocd.texi b/doc/openocd.texi
index c14ee9c..de990c5 100644
--- a/doc/openocd.texi
+++ b/doc/openocd.texi
@@ -2810,9 +2810,9 @@ If not specified, default 0xFFFF is used.
 @end deffn
 
 @deffn {Interface Driver} {remote_bitbang}
-Drive JTAG from a remote process. This sets up a UNIX or TCP socket connection
-with a remote process and sends ASCII encoded bitbang requests to that process
-instead of directly driving JTAG.
+Drive JTAG and SWD from a remote process. This sets up a UNIX or TCP socket
+connection with a remote process and sends ASCII encoded bitbang requests to
+that process instead of directly driving JTAG and SWD.
 
 The remote_bitbang driver is useful for debugging software running on
 processors which are being simulated.