diff --git a/jtag/ChangeLog b/jtag/ChangeLog
index f71d5426..ffcad78f 100644
--- a/jtag/ChangeLog
+++ b/jtag/ChangeLog
@@ -1,3 +1,21 @@
+2003-01-18  Marcel Telka  <marcel@telka.sk>
+
+	* src/jtag.c (main): Added new 'frequency' command.
+	* src/help.c (help): Added help for 'frequency' command.
+	* include/cable.h (cable_wait): Added new function prototype.
+	* src/tap/cable.c (cable_wait): Added new function.
+	* src/tap/cable/byteblaster.c (byteblaster_clock): Added support for TCK
+		frequency limit.
+	(byteblaster_get_tdo): Ditto.
+	* src/tap/cable/dlc5.c (dlc5_clock): Ditto.
+	(dlc5_get_tdo): Ditto.
+	* src/tap/cable/ea253.c (ea253_clock): Ditto.
+	(ea253_get_tdo): Ditto.
+	* src/tap/cable/ei012.c (ei012_clock): Ditto.
+	(ei012_get_tdo): Ditto.
+	* src/tap/cable/wiggler.c (wiggler_clock): Ditto.
+	(wiggler_get_tdo): Ditto.
+
 2003-01-16  Marcel Telka  <marcel@telka.sk>
 
 	* data/MANUFACTURERS: Added Cypress (patch 669157). Thanks to Chris Ellec.
diff --git a/jtag/NEWS b/jtag/NEWS
index b9b2acfe..5f3ab4f1 100644
--- a/jtag/NEWS
+++ b/jtag/NEWS
@@ -1,6 +1,7 @@
 $Id$
 
 	* Added new manufacturer: Cypress. (patch 669157, Chris Ellec)
+	* Added new 'frequency' command to limit maximum TCK frequency
 
 jtag-0.2.1 (2003-01-13):
 
diff --git a/jtag/include/cable.h b/jtag/include/cable.h
index 805f9485..88e8bde3 100644
--- a/jtag/include/cable.h
+++ b/jtag/include/cable.h
@@ -38,6 +38,9 @@ typedef struct {
 	void (*set_trst)( int );
 } cable_driver_t;
 
+extern uint32_t frequency;
+void cable_wait( void );
+
 extern cable_driver_t *cable;
 #define	tap_clock	cable->clock
 #define	tap_get_tdo	cable->get_tdo
diff --git a/jtag/src/help.c b/jtag/src/help.c
index 24aa09fe..ebfcb6b3 100644
--- a/jtag/src/help.c
+++ b/jtag/src/help.c
@@ -40,6 +40,7 @@ help( const char *cmd )
 			"\n"
 			"quit          exit from %s\n"
 			"help          display this help\n"
+			"frequency     setup JTAG frequency\n"
 			"cable         select JTAG cable\n"
 			"detect        detect parts on the JTAG chain\n"
 			"discovery     discovery unknown parts in the JTAG chain\n"
@@ -64,6 +65,19 @@ help( const char *cmd )
 			"Usage: help [COMMAND]\n"
 			"Print short help for COMMAND, or list of available commands.\n"
 		);
+	else if (strcmp( cmd, "frequency" ) == 0)
+		printf(
+			"Usage: frequency FREQ\n"
+			"Change TCK frequency to FREQ.\n"
+			"\n"
+			"FREQ is in hertz. It's a maximum TCK frequency for JTAG interface.\n"
+			"In some cases the TCK frequency is less than FREQ, but the frequency\n"
+			"is never more than FREQ. Maximum supported frequency depends on JTAG\n"
+			"adapter.\n"
+			"\n"
+			"FREQ must be an unsigned integer. Minimum allowed frequency is 1 Hz.\n"
+			"Use 0 for FREQ to disable frequency limit.\n"
+		);
 	else if (strcmp( cmd, "cable" ) == 0) {
 		int i;
 
diff --git a/jtag/src/jtag.c b/jtag/src/jtag.c
index d5980ea7..551c5bba 100644
--- a/jtag/src/jtag.c
+++ b/jtag/src/jtag.c
@@ -100,6 +100,26 @@ main( void )
 			continue;
 		}
 
+		if (strcmp( t, "frequency" ) == 0) {
+			uint32_t freq;
+
+			t = get_token( NULL );
+			if (!t) {
+				printf( "Missing argument(s)\n" );
+				continue;
+			}
+			if ((sscanf( t, "0x%x", &freq ) != 1) && (sscanf( t, "%u", &freq ) != 1)) {
+				printf( "syntax error\n" );
+				continue;
+			}
+
+			printf( "Setting TCK frequency to %u Hz\n", freq );
+
+			frequency = freq;
+
+			continue;
+		}
+
 		if (strcmp( t, "cable" ) == 0) {
 			int i;
 			unsigned int port;
diff --git a/jtag/src/tap/cable.c b/jtag/src/tap/cable.c
index c49236bd..9b96cf3a 100644
--- a/jtag/src/tap/cable.c
+++ b/jtag/src/tap/cable.c
@@ -23,6 +23,8 @@
  */
 
 #include <stdlib.h>
+#include <unistd.h>
+#include <stdint.h>
 
 #include "cable.h"
 
@@ -32,6 +34,8 @@ extern cable_driver_t ea253_cable_driver;
 extern cable_driver_t ei012_cable_driver;
 extern cable_driver_t wiggler_cable_driver;
 
+uint32_t frequency = 0;
+
 cable_driver_t *cable_drivers[] = {
 	&byteblaster_cable_driver,
 	&dlc5_cable_driver,
@@ -40,3 +44,18 @@ cable_driver_t *cable_drivers[] = {
 	&wiggler_cable_driver,
 	NULL				/* last must be NULL */
 };
+
+void
+cable_wait( void )
+{
+	useconds_t s;
+
+	if (!frequency)
+		return;
+
+	s = 1000000 / frequency / 2;
+	if (s == 0)
+		s = 1;
+
+	usleep( s );
+}
diff --git a/jtag/src/tap/cable/byteblaster.c b/jtag/src/tap/cable/byteblaster.c
index efa2eabe..a59f9294 100644
--- a/jtag/src/tap/cable/byteblaster.c
+++ b/jtag/src/tap/cable/byteblaster.c
@@ -77,7 +77,9 @@ byteblaster_clock( int tms, int tdi )
 	tdi &= 1;
 
 	outb( (0 << TCK) | (tms << TMS) | (tdi << TDI), port );
+	cable_wait();
 	outb( (1 << TCK) | (tms << TMS) | (tdi << TDI), port );
+	cable_wait();
 
 	tap_state_clock( tms );
 }
@@ -86,6 +88,7 @@ static int
 byteblaster_get_tdo( void )
 {
 	outb( 0 << TCK, port );
+	cable_wait();
 	return ((inb( port + 1 ) ^ 0x80) >> TDO) & 1;		/* BUSY is inverted */
 }
 
diff --git a/jtag/src/tap/cable/dlc5.c b/jtag/src/tap/cable/dlc5.c
index 4e4c9249..5a5fb946 100644
--- a/jtag/src/tap/cable/dlc5.c
+++ b/jtag/src/tap/cable/dlc5.c
@@ -77,7 +77,9 @@ dlc5_clock( int tms, int tdi )
 	tdi &= 1;
 
 	outb( (1 << PROG) | (0 << TCK) | (tms << TMS) | (tdi << TDI), port );
+	cable_wait();
 	outb( (1 << PROG) | (1 << TCK) | (tms << TMS) | (tdi << TDI), port );
+	cable_wait();
 
 	tap_state_clock( tms );
 }
@@ -86,6 +88,7 @@ static int
 dlc5_get_tdo( void )
 {
 	outb( (1 << PROG) | (0 << TCK), port );
+	cable_wait();
 	return ((inb( port + 1 ) ^ 0x80) >> TDO) & 1;		/* BUSY is inverted */
 }
 
diff --git a/jtag/src/tap/cable/ea253.c b/jtag/src/tap/cable/ea253.c
index e20a20f1..28c3ac01 100644
--- a/jtag/src/tap/cable/ea253.c
+++ b/jtag/src/tap/cable/ea253.c
@@ -76,7 +76,9 @@ ea253_clock( int tms, int tdi )
 	tdi &= 1;
 
 	outb( (trst << TRST) | (0 << TCK) | (tms << TMS) | (tdi << TDI), port );
+	cable_wait();
 	outb( (trst << TRST) | (1 << TCK) | (tms << TMS) | (tdi << TDI), port );
+	cable_wait();
 
 	tap_state_clock( tms );
 }
@@ -85,6 +87,7 @@ static int
 ea253_get_tdo( void )
 {
 	outb( (tap_state_get_trst() << TRST) | (0 << TCK), port );
+	cable_wait();
 	return ((inb( port + 1 ) ^ 0x80) >> TDO) & 1;		/* BUSY is inverted */
 }
 
diff --git a/jtag/src/tap/cable/ei012.c b/jtag/src/tap/cable/ei012.c
index 92728216..74474cad 100644
--- a/jtag/src/tap/cable/ei012.c
+++ b/jtag/src/tap/cable/ei012.c
@@ -77,7 +77,9 @@ ei012_clock( int tms, int tdi )
 	tdi &= 1;
 
 	outb( (trst << TRST) | (0 << TCK) | (tms << TMS) | (tdi << TDI), port );
+	cable_wait();
 	outb( (trst << TRST) | (1 << TCK) | (tms << TMS) | (tdi << TDI), port );
+	cable_wait();
 
 	tap_state_clock( tms );
 }
@@ -86,6 +88,7 @@ static int
 ei012_get_tdo( void )
 {
 	outb( (tap_state_get_trst() << TRST) | (0 << TCK), port );
+	cable_wait();
 	return ((inb( port + 1 ) ^ 0x80) >> TDO) & 1;		/* BUSY is inverted */
 }
 
diff --git a/jtag/src/tap/cable/wiggler.c b/jtag/src/tap/cable/wiggler.c
index 3987d0cf..1b9b6aa6 100644
--- a/jtag/src/tap/cable/wiggler.c
+++ b/jtag/src/tap/cable/wiggler.c
@@ -80,7 +80,9 @@ wiggler_clock( int tms, int tdi )
 	tdi &= 1;
 
 	outb( (trst << TRST) | (0 << TCK) | (tms << TMS) | (tdi << TDI), port );
+	cable_wait();
 	outb( (trst << TRST) | (1 << TCK) | (tms << TMS) | (tdi << TDI), port );
+	cable_wait();
 
 	tap_state_clock( tms );
 }
@@ -89,6 +91,7 @@ static int
 wiggler_get_tdo( void )
 {
 	outb( (tap_state_get_trst() << TRST) | (0 << TCK), port );
+	cable_wait();
 	return ((inb( port + 1 ) ^ 0x80) >> TDO) & 1;		/* BUSY is inverted */
 }