Mathias Dietz Weblog

Next
Steps:

I have to study the jtag basics:
-how does jtag work (TMI,TDO,signals)?
-What is that BSR used for (Boundary Scan Register) ?
-The architecture of the ARM platform (Instruction Register, Data Register …)

And a second answer from Marcel:

Hi Mathias.
On Mon, Aug 15, 2005 at 09:20:40AM +0200, Mathias Dietz wrote:
>          jtag> detect
>          IR length: 5
>          Chain length: 1
>          Device Id: 01101001001001100100000000010011
>            Manufacturer: Intel
>            Part:         PXA250
>            Stepping:     PXA255A0
>            Filename:     /usr/local/share/jtag/intel/pxa250/pxa250c0

>          jtag> discovery
>          Detecting IR length ... 5
>          Detecting DR length for IR 11111 ... 1
>          Detecting DR length for IR 00000 ...         <<------- the board
>          is resetted and turned off 
During EXTEST (00000) the previous content of the BSR is transferred to the
PXA255 pins. While standard usage (as flash programming) we are using
SAMPLE/PRELOAD to set default BSR bit values, but during 'discovery' the
internal defaults are used because 'discovery' has no knowledge about
SAMPLE/PRELOAD instruction code.

It looks like your board has a feature that perfoms reset (or turn-off) of the
board when some value (probably 0) is present on a GPIO (or another pin) of the
CPU. In that case it looks like a bad board design for me. Anyway, if that is
your case you should not use the 'discovery' command. To enable flash
programming you could adjust BSR bit defaults as needed for your board.

Regards.

I got an answer from Andrew:

On 8/15/05, Mathias Dietz  wrote:

> But when I start the detectflash or dicovery command, the board resets and
> turns off.

I don`t know your specific hardware, but I`m guessing that something
in the bus driver for the PXA series parts is triggering the behaviour
you see.  Most bus drivers work by shifting in a series of bits that
apply to /all/ the I/O for the CPU and repeating this over and over to
produce valid external read/write signals to the flash.  If this
series of bits happens to set the bits that control a reset/power
off/watchdog for your system, then you would see the behavior
you`re getting.

Hardware, n.:
        The parts of a computer system that can be kicked.

I tried to debug the JTAG tools using the gdb debugger.
Because the command line interface for
gdb is not very nice, I decided to use a graphical debugger.
The CDT for eclipse was my choise and within 30 minutes I found the function call which leads
to the board reset:

cfi.c (Common Flash Interface)
function cfi_detect(...)
line #104
write1( CFI_CMD_QUERY_OFFSET, CFI_CMD_QUERY );

After some additional testing and debugging, I wrote a mail to the jtag-tools mailing list:
Mail to the mailing list:

Hi,
I try to flash my pxa255 based board using a selfmade Xilinx DLC5 cable.
The detect and print command runs fine:
jtag> cable parallel 0x378 DLC5
Initializing Xilinx DLC5 JTAG Parallel Cable III on parallel port at 0x378
jtag> detect
IR length: 5
Chain length: 1
Device Id: 01101001001001100100000000010011
  Manufacturer: Intel
  Part:         PXA250
  Stepping:     PXA255A0
  Filename:     /usr/local/share/jtag/intel/pxa250/pxa250c0
jtag> print
 No. Manufacturer              Part                 Stepping Instruction          Register
++-------------------------------------------------------------------------------------------++
   0 Intel                     PXA250               PXA255A0 BYPASS               BR

Active bus:
*0: Intel PXA2x0 compatible bus driver via BSR (JTAG part No. 0)
        start: 0x00000000, length: 0x04000000, data width: 32 bit, (Static Chip Select 0)
        start: 0x48000000, length: 0x04000000, data width: 32 bit, (Memory Mapped registers (Memory Ctl))
But when I start the detectflash or dicovery command , the board resets and turns off.
I have to turn it on the use any JTAG command.
jtag> detectflash
jedec_detect: mid ffffffff, did ffffffff			<<-- the board is resetted and turned off
Flash not found!
jtag> discovery							<<-- manually turned on the board again
Detecting IR length ... 5
Detecting DR length for IR 11111 ... 1
Detecting DR length for IR 00000 ...				<<-- the board is resetted and turned off 
Some additional infos (might help):
jtag> instruction SAMPLE/PRELOAD
jtag> shift ir
jtag> shift dr
jtag> dr
1001110011111111111111111000000111000000111111110110000000101101111111110000001111111111101101000001100110000100010010110110011111010011001110000110001100000000000
1111100000011110011111110000000000000000000000111000000111100010110000000101001000000100000001101111111100101000000000000000100010010010110001010000000000000111101
111111110110000001011111110011111111101010111100110011001000101100111100010111000000
jtag> get signal BOOT_SEL[0]
BOOT_SEL[0] = 1
I tried jtag tools 0.51 and the current CVS version.