Berkus Decker
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doc/rpi3_jtag.md
155
doc/rpi3_jtag.md
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@ -2,5 +2,156 @@ JTAG boards:
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* TinCanTools Flyswatter
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* OpenMoko DebugBoard_v3
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* RasPi3 - https://movr0.com/2016/09/02/use-raspberry-pi-23-as-a-jtagswd-adapter/
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* J-Link V9
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* RasPi3 -
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- Pinouts for rpi3 - modelB https://www.element14.com/community/docs/DOC-73950/l/raspberry-pi-3-model-b-gpio-40-pin-block-pinout and model B+ https://www.element14.com/community/docs/DOC-88824/l/raspberry-pi-3-model-b-gpio-40-pin-block-poe-header-pinout (they are the same)
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* Segger J-Link V9
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# RPi3 to RPi3 jtag
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## Host configuration:
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These are regular GPIO functions, which we specify in OpenOCD interface configuration to enable driving JTAG interface.
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```
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FUNC | GPIO | PIN #
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------+--------+-------
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TCK | GPIO11 | 23
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TMS | GPIO25 | 22
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TDI | GPIO10 | 19
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TDO | GPIO9 | 21
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TRST* | GPIO7 | 26
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GND | GND | 20
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```
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RPi doesn't expose SRST so we ignore it.
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[Source](https://movr0.com/2016/09/02/use-raspberry-pi-23-as-a-jtagswd-adapter/)
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## Target configuration:
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These are real JTAG pins of bcm2837, enabled on target RPi via config.txt options (see below).
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```
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FUNC | GPIO | PIN # | MODE
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------+--------+---------+------
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TCK | GPIO25 | 22 | Alt4
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TMS | GPIO27 | 13 | Alt4
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TDI | GPIO4 | 7 | Alt5
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TDO | GPIO24 | 18 | Alt4
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TRST | GPIO22 | 15 | Alt4
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GND | GND | 20 |
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```
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In config.txt:
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```
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# Set GPIO pins for JTAG debugger connection on rpi3
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gpio=22-25,27=a4
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gpio=4=a5
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# gpio23 RTCK - unused? Don't forget to avoid frequency scaling in this case.
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```
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Alternatively, just specify
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```
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enable_jtag_gpio=1
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```
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## Connection between boards
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```
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Func | Host Pin | Wire color | Target pin
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-----+----------+------------+-----------
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TCK | 23 | yellow | 22
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TMS | 22 | | 13
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TDI | 19 | | 7
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TDO | 21 | | 18
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TRST | 26 | red | 15
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GND | 20 | black | 20
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```
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## OpenOCD configuration on the host
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You need two files: interface file for driving the host GPIO correctly, and target file for detecting the JTAG circuitry on the target RPi.
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Interface configuration: rpi3_interface.cfg
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```
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interface bcm2835gpio
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bcm2835gpio_peripheral_base 0x3F000000
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# Transition delay calculation: SPEED_COEFF/khz - SPEED_OFFSET
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# These depend on system clock, calibrated for stock 700MHz
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# bcm2835gpio_speed SPEED_COEFF SPEED_OFFSET
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bcm2835gpio_speed_coeffs 146203 36
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# Each of the JTAG lines need a gpio number set: tck tms tdi tdo
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# Header pin numbers: 23 22 19 21
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bcm2835gpio_jtag_nums 11 25 10 9
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# If you define trst or srst, use appropriate reset_config
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# Header pin numbers: TRST - 26, SRST - 12
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bcm2835gpio_trst_num 7
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reset_config trst_only
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```
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[Source](https://movr0.com/2016/09/02/use-raspberry-pi-23-as-a-jtagswd-adapter/)
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Target configuration: rpi3_target.cfg
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```
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# Broadcom 2835 on Raspberry Pi
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telnet_port 4444
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gdb_port 5555
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adapter_khz 1000
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transport select jtag
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if { [info exists CHIPNAME] } {
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set _CHIPNAME $CHIPNAME
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} else {
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set _CHIPNAME rspi
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}
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if { [info exists CPU_TAPID ] } {
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set _CPU_TAPID $CPU_TAPID
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} else {
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set _CPU_TAPID 0x07b7617F
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}
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jtag newtap $_CHIPNAME arm -irlen 5 -expected-id $_CPU_TAPID
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set _TARGETNAME $_CHIPNAME.arm
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target create $_TARGETNAME arm11 -chain-position $_TARGETNAME
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rspi.arm configure -event gdb-attach { halt }
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```
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(@fixme: rspi.arm on last line should be `$_TARGETNAME` instead?)
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[Source #1](https://electronics.stackexchange.com/questions/249008/how-to-use-rpi-2-to-debug-rpi-model-b-via-jtag-with-openocd/419724#419724), [source #2](https://sysprogs.com/tutorials/preparing-raspberry-pi-for-jtag-debugging/)
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## Run OpenOCD, GDB and attach to target
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Need to verify if the following bug is still valid:
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> There is a bug in OpenOCD that will prevent Raspberry PI from continuing correctly after a stop unless the initialization is done twice. Close OpenOCD with Ctrl-C and re-run it again. Now the debugging will be usable.
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[Source](https://sysprogs.com/tutorials/preparing-raspberry-pi-for-jtag-debugging/)
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Run `openocd -f rpi3_interface.cfg -f rpi3_target.cfg`
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Run `gdb kernel.elf` and connect to device:
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```
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target remote :5555
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x/10i $pc
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stepi
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x/2i $pc
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```
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If `stepi` command causes CPU to make one instruction step, everything is working.
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[Source](https://sysprogs.com/tutorials/preparing-raspberry-pi-for-jtag-debugging/)
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