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Manual Reference Pages  -  SMP_READ_GPIO (8)


smp_read_gpio - invoke READ GPIO REGISTER (ENHANCED) SMP function


Enhanced Function
Conforming To


smp_read_gpio [--count=CO] [--enhanced] [--help] [--hex] [--index=IN] [--interface=PARAMS] [--raw] [--sa=SAS_ADDR] [--type=TY] [--verbose] [--version] SMP_DEVICE[,N]


Sends a SAS Serial Management Protocol (SMP) READ GPIO REGISTER or READ GPIO REGISTER ENHANCED function request to an SMP target. The SMP target is identified by the SMP_DEVICE and the SAS_ADDR. Depending on the interface, the SAS_ADDR may be deduced from the SMP_DEVICE. The mpt interface uses SMP_DEVICE to identify a HBA (an SMP initiator) and needs the additional ,N to differentiate between HBAs if there are multiple present.

This function is defined in SFF-8485 ( see ) together with its corresponding WRITE GPIO REGISTER SMP function. The other SMP functions are defined in SAS documents at . SFF-8485 defines a curious device called a "virtual SMP port" that lives in a host bus adapter (HBA) and allows SMP to manipulate the sideband signals on wide internal cables. To stop other initiators in a multi-initiator domain from accessing those sideband signals, the virtual SMP (target) port is not indicated in a DISCOVER response.

For notes on the SMP READ GPIO REGISTER ENHANCED function see the section on the ENHANCED FUNCTION below.


Mandatory arguments to long options are mandatory for short options as well.
-c, --count=CO
  where CO is the register count. This is the number of (4 byte) registers to request. The default value is 1.
-E, --enhanced
  sends a READ GPIO REGISTER ENHANCED function request (default: send a READ GPIO REGISTER function request).
-h, --help output the usage message then exit.
-H, --hex output the response (less the CRC field) in hexadecimal.
-i, --index=IN
  where IN is the register index. This value is origin zero and its default value is 0. If the request succeeds, then --count=CO registers starting from --index=IN of the given --type=TY should be in the response.
-I, --interface=PARAMS
  interface specific parameters. In this case "interface" refers to the path through the operating system to the SMP initiator. See the smp_utils man page for more information.
-r, --raw send the response (less the CRC field) to stdout in binary. All error messages are sent to stderr.
-s, --sa=SAS_ADDR
  specifies the SAS address of the SMP target device. Typically this is an expander. This option may not be needed if the SMP_DEVICE has the target’s SAS address within it. The SAS_ADDR is in decimal but most SAS addresses are shown in hexadecimal. To give a number in hexadecimal either prefix it with ’0x’ or put a trailing ’h’ on it.
-t, --type=TY
  where TY is the register type. The default value is 0 (GPIO_CFG). If the request succeeds, then --count=CO registers starting from --index=IN of the given --type=TY should be in the response.
-v, --verbose
  increase the verbosity of the output. Can be used multiple times
-V, --version
  print the version string and then exit.


In the technical review of SAS-2 prior to standardization in this t10 document: 08-212r8.pdf (page 871 or 552) there is a comment that the READ GPIO REGISTER and WRITE GPIO REGISTER function headers (i.e. first 4 bytes) do not comply with all the other SMP functions in SAS-2.

There is a suggestion that enhanced variants be introduced in the next version of the SFF-8485 document. If that ever happened then it has not been made public. In SAS-2.1 both the READ and WRITE GPIO REGISTER functions have been made obsolete and the corresponding ENHANCED function numbers are "restricted" for SFF-8485.

If the --enhanced option is given then the ENHANCED function number is sent; the register type, index and count fields (1 byte each) are increased by two byte positions leaving enough space for a compliant SAS-2 SMP header to be built.


See "Examples" section in


The SMP READ GPIO REGISTER (ENHANCED) function is defined in SFF-8485 (see ) together with its corresponding WRITE GPIO REGISTER (ENHANCED) SMP function.


Written by Douglas Gilbert.


Report bugs to <dgilbert at interlog dot com>.


Copyright © 2006-2011 Douglas Gilbert
This software is distributed under a FreeBSD license. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.


smp_utils, smp_write_gpio(smp_utils)
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smp_utils-0.97 SMP_READ_GPIO (8) August 2011

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