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SubjectRe: [patch v21 4/4] Documentation: jtag: Add ABI documentation
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On 05/15/2018 07:21 AM, Oleksandr Shamray wrote:
> Added document that describe the ABI for JTAG class drivrer
>
> ---
> Documentation/ABI/testing/jtag-dev | 27 +++++++++
> Documentation/jtag/overview | 28 +++++++++
> Documentation/jtag/transactions | 109 ++++++++++++++++++++++++++++++++++++
> 3 files changed, 164 insertions(+), 0 deletions(-)
> create mode 100644 Documentation/ABI/testing/jtag-dev
> create mode 100644 Documentation/jtag/overview
> create mode 100644 Documentation/jtag/transactions
>

> diff --git a/Documentation/jtag/overview b/Documentation/jtag/overview
> new file mode 100644
> index 0000000..a86f188
> --- /dev/null
> +++ b/Documentation/jtag/overview
> @@ -0,0 +1,28 @@
> +Linux kernel JTAG support
> +=========================
> +
> +The JTAG is an industry standard for verifying hardware

JTAG is an industry standard for verifying hardware.

> +JTAG provides access to many logic signals of a complex integrated circuit,
> +including the device pins.
> +
> +A JTAG interface is a special interface added to a chip.
> +Depending on the version of JTAG, two, four, or five pins are added.
> +
> +The connector pins are:
> + TDI (Test Data In)
> + TDO (Test Data Out)
> + TCK (Test Clock)
> + TMS (Test Mode Select)
> + TRST (Test Reset) optional.
> +
> +JTAG interface is designed to have two parts - basic core driver and
> +hardware specific driver. The basic driver introduces a general interface
> +which is not dependent of specific hardware. It provides communication
> +between user space and hardware specific driver.
> +Each JTAG device is represented as a char device from (jtag0, jtag1, ...).
> +Access to a JTAG device is performed through IOCTL calls.
> +
> +Call flow example:
> +User: open -> /dev/jatgX
> +User: ioctl -> /dev/jtagX -> JTAG core driver -> JTAG hw specific driver

JTAG hardware specific driver

> +User: close -> /dev/jatgX
> diff --git a/Documentation/jtag/transactions b/Documentation/jtag/transactions
> new file mode 100644
> index 0000000..6a857c8
> --- /dev/null
> +++ b/Documentation/jtag/transactions
> @@ -0,0 +1,109 @@
> +The JTAG API
> +=============
> +
> +JTAG master devices can be accessed through a character misc-device.
> +Each JTAG master interface can be accessed by using /dev/jtagN

/dev/jtagN.

> +
> +JTAG system calls set:
> +- SIR (Scan Instruction Register, IEEE 1149.1 Instruction Register scan);
> +- SDR (Scan Data Register, IEEE 1149.1 Data Register scan);
> +- RUNTEST (Forces the IEEE 1149.1 bus to a run state for a specified
> +number of clocks.
> +
> +open(), close()
> +-------
> +open() opens JTAG device. Only one open operation per JTAG device
> +can be performed. Two or more open for one device will return error

will return error.

> +
> +Open/Close device:
> +- open("/dev/jtag0", O_RDWR);
> +- close(jtag_fd');

close(jtag_fd);

> +
> +ioctl()
> +-------
> +All access operations to JTAG devices performed through ioctl interface.
> +The IOCTL interface supports this requests:

these requests:

> + JTAG_IOCRUNTEST - Force JTAG state machine to RUN_TEST/IDLE state
> + JTAG_SIOCFREQ - Set JTAG TCK frequency
> + JTAG_GIOCFREQ - Get JTAG TCK frequency
> + JTAG_IOCXFER - send JTAG data Xfer
> + JTAG_GIOCSTATUS - get current JTAG TAP status
> + JTAG_SIOCMODE - set JTAG mode flags.
> +
> +JTAG_SIOCFREQ, JTAG_GIOCFREQ
> +------
> +Set/Get JTAG clock speed:
> +
> + unsigned int jtag_fd;
> + ioctl(jtag_fd, JTAG_SIOCFREQ, &frq);
> + ioctl(jtag_fd, JTAG_GIOCFREQ, &frq);
> +
> +JTAG_IOCRUNTEST
> +------
> +Force JTAG state machine to RUN_TEST/IDLE state
> +
> +struct jtag_run_test_idle {
> + __u8 reset;
> + __u8 endstate;
> + __u8 tck;
> +};
> +
> +reset: 0 - run IDLE/PAUSE from current state
> + 1 - go through TEST_LOGIC/RESET state before IDLE/PAUSE
> +endstate: completion flag
> +tck: clock counter
> +
> +Example:
> + struct jtag_run_test_idle runtest;
> +
> + runtest.endstate = JTAG_STATE_IDLE;
> + runtest.reset = 0;
> + runtest.tck = data_p->tck;
> + usleep(25 * 1000);
> + ioctl(jtag_fd, JTAG_IOCRUNTEST, &runtest);
> +
> +JTAG_IOCXFER
> +------
> +Send SDR/SIR transaction
> +
> +struct jtag_xfer {
> + __u8 type;
> + __u8 direction;
> + __u8 endstate;
> + __u8 padding;
> + __u32 length;
> + __u64 tdio;
> +};
> +
> +type: transfer type - JTAG_SIR_XFER/JTAG_SDR_XFER
> +direction: xfer direction - JTAG_SIR_XFER/JTAG_SDR_XFER,
> +length: xfer data len in bits
> +tdio : xfer data array
> +endstate: xfer end state after transaction finish
> + can be: JTAG_STATE_IDLE/JTAG_STATE_PAUSEIR/JTAG_STATE_PAUSEDR
> +
> +Example:
> + struct jtag_xfer xfer;
> + static char buf[64];
> + static unsigned int buf_len = 0;
> + [...]
> + xfer.type = JTAG_SDR_XFER;
> + xfer.tdio = (__u64)buf;
> + xfer.length = buf_len;
> + xfer.endstate = JTAG_STATE_IDLE;
> +
> + if (is_read)
> + xfer.direction = JTAG_READ_XFER;
> + else
> + xfer.direction = JTAG_WRITE_XFER;
> +
> + ioctl(jtag_fd, JTAG_IOCXFER, &xfer);
> +
> +JTAG_SIOCMODE
> +------
> +If hw driver can support different running modes you can change it.

If hardware driver

> +
> +Example:
> + unsigned int mode;
> + mode = JTAG_XFER_HW_MODE;
> + ioctl(jtag_fd, JTAG_SIOCMODE, &mode);
>


--
~Randy

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