OrgApache/incubator-nuttx
OrgApache
/
incubator-nuttx
mirror of https://github.com/apache/incubator-nuttx.git
1
0
Fork 0
Code Issues Releases Wiki Activity
incubator-nuttx/boards/mips/pic32mx/ubw32/README.txt

609 lines
23 KiB
Plaintext
Raw Blame History

boards/mips/pic32mx/ubw32 README
====================
This README file discusses the port of NuttX to the Sparkfun UBW32 board.
This port uses the original v2.5 board which is based on the MicroChip
PIC32MX460F512L. See http://www.sparkfun.com/products/8971. This older
version has been replaced with this board http://www.sparkfun.com/products/9713.
See also http://www.schmalzhaus.com/UBW32/.
Contents
========
PIC32MX460F512L Pin Out
MAX3232 Connection
Toolchains
Loading NuttX with PICkit2
LEDs
Buttons
PIC32MX Configuration Options
Configurations
PIC32MX460F512L Pin Out
=======================
PIC32MX460F512L 100-Pin TQFP (USB) Pin Out. The mapping to the pins on
the PCL Logic board are very simple, each pin is brought out to a connector
label with the PIC32MX460F512L pin number.
On board logic only manages power, crystal, and USB signals.
LEFT SIDE, TOP-TO-BOTTOM (if pin 1 is in upper left)
---- ---------------------------- -------------------------------------------------------
PIN NAME Board Connection (omitting pins brought to J3 and J4)
---- ---------------------------- -------------------------------------------------------
1 RG15
2 Vdd
3 PMD5/RE5
4 PMD6/RE6 RE6 User switch
5 PMD7/RE7 RE7 Program switch
6 T2CK/RC1
7 T3CK/RC2
8 T4CK/RC3
9 T5CK/SDI1/RC4
10 SCK2/PMA5/CN8/RG6
11 SDI2/PMA4/CN9/RG7
12 SDO2/PMA3/CN10/RG8
13 MCLR
14 SS2/PMA2/CN11/RG9
15 Vss
16 Vdd
17 TMS/RA0
18 INT1/RE8
19 INT2/RE9
20 AN5/C1IN+/VBUSON/CN7/RB5
21 AN4/C1IN-/CN6/RB4
22 AN3/C2IN+/CN5/RB3
23 AN2/C2IN-/CN4/RB2 RB1 ICSP/Debug/IO (J5) pin 6 (labeled B2)
24 PGEC1/AN1/CN3/RB1 RB1 ICSP/Debug/IO (J5) pin 7 (labeled B1)
25 PGED1/AN0/CN2/RB0 RB0 ICSP/Debug/IO (J5) pin 8 (labeled B0)
BOTTOM SIDE, LEFT-TO-RIGHT (if pin 1 is in upper left)
---- ---------------------------- -------------------------------------------------------
PIN NAME Board Connection (omitting pins brought to J3 and J4)
---- ---------------------------- -------------------------------------------------------
26 PGEC2/AN6/OCFA/RB6 PGC ICSP/Debug/IO (J5) pin 5 (labeled PGC)
27 PGED2/AN7/RB7 PGD ICSP/Debug/IO (J5) pin 4 (labeled PGD)
28 VREF-/CVREF-/PMA7/RA9
29 VREF+/CVREF+/PMA6/RA10
30 AVdd
31 AVss
32 AN8/C1OUT/RB8
33 AN9/C2OUT/RB9
34 AN10/CVREFOUT/PMA13/RB10
35 AN11/PMA12/RB11
36 Vss
37 Vdd
38 TCK/RA1
39 U2RTS/RF13
40 U2CTS/RF12
41 AN12/PMA11/RB12
42 AN13/PMA10/RB13
43 AN14/PMALH/PMA1/RB14
44 AN15/OCFB/PMALL/PMA0/CN12/RB15
45 Vss
46 Vdd
47 U1CTS/CN20/RD14
48 U1RTS/CN21/RD15
49 U2RX/PMA9/CN17/RF4
50 U2TX/PMA8/CN18/RF5
RIGHT SIDE, TOP-TO-BOTTOM (if pin 1 is in upper left)
---- ---------------------------- -------------------------------------------------------
PIN NAME Board Connection (omitting pins brought to J3 and J4)
---- ---------------------------- -------------------------------------------------------
75 Vss
74 SOSCO/T1CK/CN0/RC14
73 SOSCI/CN1/RC13
72 SDO1/OC1/INT0/RD0
71 IC4/PMCS1/PMA14/RD11
70 SCK1/IC3/PMCS2/PMA15/RD10
69 SS1/IC2/RD9
68 RTCC/IC1/RD8
67 SDA1/INT4/RA15
66 SCL1/INT3/RA14
65 Vss
64 OSC2/CLKO/RC15
63 OSC1/CLKI/RC12
62 Vdd
61 TDO/RA5
60 TDI/RA4
59 SDA2/RA3
58 SCL2/RA2
57 D+/RG2 D+ Alternate USB (J6) pin 3 (labeled D+)
USB host (JP1) pin
USB Function (Mini B)
56 D-/RG3 D- Alternate USB (J6) pin 2 (labeled D-)
USB host (JP1) pin
USB Function (Mini B)
55 VUSB
54 VBUS VBUS Alternate USB (J6) pin 1 (labeled VBUS)
USB host (JP1) pin
USB Function (Mini B)
Jumper JP1 for USB host functionality
53 U1TX/RF8
52 U1RX/RF2
51 USBID/RF3 USBID Alternate USB (J6) pin 4 (labeled ID)
USB Function (Mini B)
Also USB LED
TOP SIDE, LEFT-TO-RIGHT (if pin 1 is in upper left)
---- ---------------------------- -------------------------------------------------------
PIN NAME Board Connection (omitting pins brought to J3 and J4)
---- ---------------------------- -------------------------------------------------------
100 PMD4/RE4
99 PMD3/RE3
98 PMD2/RE2 RE2 LED1
97 TRD0/RG13
96 TRD1/RG12
95 TRD2/RG14
94 PMD1/RE1 RE1 LED2
93 PMD0/RE0 RE0 LED3
92 TRD3/RA7
91 TRCLK/RA6
90 PMD8/RG0
89 PMD9/RG1
88 PMD10/RF1
87 PMD11/RF0
86 ENVREG
85 Vcap/Vddcore
84 PMD15/CN16/RD7
83 PMD14/CN15/RD6
82 PMRD/CN14/RD5
81 OC5/PMWR/CN13/RD4
80 PMD13/CN19/RD13
79 IC5/PMD12/RD12
78 OC4/RD3
77 OC3/RD2
76 OC2/RD1
MAX3232 Connection
==================
I use a tiny, MAX3232 board that I got from the eBay made by NKC
Electronics (http://www.nkcelectronics.com/). As of this writing, it
is also available here: http://www.nkcelectronics.com/rs232-to-ttl-3v--55v-convert232356.html
CTS -- Not connected
RTS -- Not connected
TX -- J4 pin 31: U1TX/RF8
RX -- J4 pin 30: U1RX/RF2
GND -- J4 pin 40: GND
Vcc -- J4 pin 39: 5V
Toolchains
==========
MPLAB/C32
---------
I am using the free, "Lite" version of the PIC32MX toolchain available
for download from the microchip.com web site. I am using the Windows
version. The MicroChip toolchain is the only toolchain currently
supported in these configurations, but it should be a simple matter to
adapt to other toolchains by modifying the Make.defs file include in
each configuration.
C32 Toolchain Options:
CONFIG_MIPS32_TOOLCHAIN_MICROCHIPW - MicroChip full toolchain for Windows
CONFIG_MIPS32_TOOLCHAIN_MICROCHIPL - MicroChip full toolchain for Linux
CONFIG_MIPS32_TOOLCHAIN_MICROCHIPW_LITE - MicroChip "Lite" toolchain for Windows
CONFIG_MIPS32_TOOLCHAIN_MICROCHIPL_LITE - MicroChip "Lite" toolchain for Linux
CONFIG_MIPS32_TOOLCHAIN_PINGUINOL - Pinquino toolchain for Linux
CONFIG_MIPS32_TOOLCHAIN_PINGUINOW - Pinquino toolchain for Windows
CONFIG_MIPS32_TOOLCHAIN_MICROCHIPOPENL - Microchip open toolchain for Linux
CONFIG_MIPS32_TOOLCHAIN_GNU_ELF - General mips-elf toolchain for Linux
NOTE: The "Lite" versions of the toolchain does not support C++. Also
certain optimization levels are not supported by the "Lite" toolchain.
MicrochipOpen
-------------
An alternative, build-it-yourself toolchain is available here:
http://sourceforge.net/projects/microchipopen/ . These tools were
last updated circa 2010. NOTE: C++ support still not available
in this toolchain.
Building MicrochipOpen (on Linux)
1) Get the build script from this location:
http://microchipopen.svn.sourceforge.net/viewvc/microchipopen/ccompiler4pic32/buildscripts/trunk/
2) Build the code using the build script, for example:
./build.sh -b v105_freeze
This will check out the selected branch and build the tools.
3) Binaries will then be available in a subdirectory with a name something like
pic32-v105-freeze-20120622/install-image/bin (depending on the current data
and the branch that you selected.
Note that the tools will have the prefix, mypic32- so, for example, the
compiler will be called mypic32-gcc.
Pinguino mips-elf Toolchain
---------------------------
Another option is the mips-elf toolchain used with the Pinguino project. This
is a relatively current mips-elf GCC and should provide free C++ support as
well. This toolchain can be downloaded from the Pinguino website:
http://wiki.pinguino.cc/index.php/Main_Page#Download .
See also boards/mirtoo/README.txt. There is an experimental (untested)
configuration for the Mirtoo platform in that directory.
MPLAB/C32 vs MPLABX/X32
-----------------------
It appears that Microchip is phasing out the MPLAB/C32 toolchain and replacing
it with MPLABX and XC32. At present, the XC32 toolchain is *not* compatible
with the NuttX build scripts. Here are some of the issues that I see when trying
to build with XC32:
1) Make.def changes: You have to change the tool prefix:
-CROSSDEV=pic32-
+CROSSDEV=xc32-
2) debug.ld/release.ld: The like expect some things that are not present in
the current linker scripts (or are expected with different names). Here
are some partial fixes:
Rename: kseg0_progmem to kseg0_program_mem
Rename: kseg1_datamem to kseg1_data_mem
Even then, there are more warnings from the linker and some undefined symbols
for non-NuttX code that resides in the unused Microchip libraries. You will
have to solve at least this undefined symbol problem if you want to used the
XC32 toolchain.
Windows Native Toolchains
-------------------------
NOTE: There are several limitations to using a Windows based toolchain in a
Cygwin environment. The three biggest are:
1. The Windows toolchain cannot follow Cygwin paths. Path conversions are
performed automatically in the Cygwin makefiles using the 'cygpath' utility
but you might easily find some new path problems. If so, check out 'cygpath -w'
2. Windows toolchains cannot follow Cygwin symbolic links. Many symbolic links
are used in Nuttx (e.g., include/arch). The make system works around these
problems for the Windows tools by copying directories instead of linking them.
But this can also cause some confusion for you: For example, you may edit
a file in a "linked" directory and find that your changes had no effect.
That is because you are building the copy of the file in the "fake" symbolic
directory. If you use a Windows toolchain, you should get in the habit of
making like this:
make clean_context all
An alias in your .bashrc file might make that less painful.
Loading NuttX with PICkit2
==========================
NOTE: You need a PICKit3 if you plan to use the MPLAB debugger! The PICKit2
can, however, still be used to load programs. Instructions for the PICKit3
are similar.
Intel Hex Forma Files:
----------------------
When NuttX is built it will produce two files in the top-level NuttX
directory:
1) nuttx - This is an ELF file, and
2) nuttx.hex - This is an Intel Hex format file. This is controlled by
the setting CONFIG_INTELHEX_BINARY in the .config file.
The PICkit tool wants an Intel Hex format file to burn into FLASH. However,
there is a problem with the generated nutt.hex: The tool expects the nuttx.hex
file to contain physical addresses. But the nuttx.hex file generated from the
top-level make will have address in the KSEG0 and KSEG1 regions.
tools/pic32/mkpichex:
----------------------
There is a simple tool in the NuttX tools/pic32 directory that can be
used to solve both issues with the nuttx.hex file. But, first, you must
build the tool:
cd tools/pic32
make -f Makefile.host
Now you will have an executable file call mkpichex (or mkpichex.exe on
Cygwin). This program will take the nutt.hex file as an input, it will
convert all of the KSEG0 and KSEG1 addresses to physical address, and
it will write the modified file, replacing the original nuttx.hex.
To use this file, you need to do the following things:
export PATH =??? # Add the NuttX tools/pic32 directory to your
# PATH variable
make # Build nuttx and nuttx.hex
mkpichex $PWD # Convert addresses in nuttx.hex. $PWD is the path
# to the top-level build directory. It is the only
# required input to mkpichex.
This procedure is automatically performed at the end of a build.
LEDs
====
----- ----- -------------------------------------------------------------
LABEL COLOR CONTROL
----- ----- -------------------------------------------------------------
USB Green RF3. This could be used by software if USB is not used.
Otherwise, RF3 is used as the USBID signal.
LED1 While RE2, Pulled up. Low value illuminates
LED2 Red RE1, Pulled up. Low value illuminates
LED3 Yellow RE0, Pulled up. Low value illuminates
PWR Blue Illuminated when 5V is present, not controlled by software
If CONFIG_ARCH_LEDS is defined, then NuttX will control these LEDs as follows:
ON OFF
------------------------- ---- ---- ---- ---- ---- ----
LED1 LED2 LED3 LED1 LED2 LED3
------------------------- ---- ---- ---- ---- ---- ----
LED_STARTED 0 OFF OFF OFF --- --- ---
LED_HEAPALLOCATE 1 ON OFF N/C --- --- ---
LED_IRQSENABLED 2 OFF ON N/C --- --- ---
LED_STACKCREATED 3 ON ON N/C --- --- ---
LED_INIRQ 4 N/C N/C ON N/C N/C OFF
LED_SIGNAL 4 N/C N/C ON N/C N/C OFF
LED_ASSERTION 4 N/C N/C ON N/C N/C OFF
LED_PANIC 5 ON N/C N/C OFF N/C N/C
Buttons
=======
RE6 User switch
RE7 Program switch
PIC32MX Configuration Options
=============================
General Architecture Settings:
CONFIG_ARCH - Identifies the arch/ subdirectory. This should
be set to:
CONFIG_ARCH=mips
CONFIG_ARCH_family - For use in C code:
CONFIG_ARCH_MIPS=y
CONFIG_ARCH_architecture - For use in C code:
CONFIG_ARCH_MIPS32=y
CONFIG_ARCH_CHIP - Identifies the arch/*/chip subdirectory
CONFIG_ARCH_CHIP=pic32mx
CONFIG_ARCH_CHIP_name - For use in C code to identify the exact
chip:
CONFIG_ARCH_CHIP_PIC32MX460F512L=y
CONFIG_ARCH_BOARD - Identifies the boards/ subdirectory and
hence, the board that supports the particular chip or SoC.
CONFIG_ARCH_BOARD=ubw32
CONFIG_ARCH_BOARD_name - For use in C code
CONFIG_ARCH_BOARD_UBW32=y
CONFIG_ARCH_LOOPSPERMSEC - Must be calibrated for correct operation
of delay loops
CONFIG_ENDIAN_BIG - define if big endian (default is little
endian)
CONFIG_RAM_SIZE - Describes the installed DRAM (CPU SRAM in this case):
CONFIG_RAM_SIZE=(32*1024) (32Kb)
There is an additional 32Kb of SRAM in AHB SRAM banks 0 and 1.
CONFIG_RAM_START - The start address of installed DRAM
CONFIG_RAM_START=0xa0000000
CONFIG_ARCH_LEDS - Use LEDs to show state. Unique to boards that
have LEDs
CONFIG_ARCH_INTERRUPTSTACK - This architecture supports an interrupt
stack. If defined, this symbol is the size of the interrupt
stack in bytes. If not defined, the user task stacks will be
used during interrupt handling.
CONFIG_ARCH_STACKDUMP - Do stack dumps after assertions
CONFIG_ARCH_LEDS - Use LEDs to show state. Unique to board architecture.
PIC32MX Configuration
CONFIG_PIC32MX_MVEC - Select muli- vs. single-vectored interrupts
Individual subsystems can be enabled:
CONFIG_PIC32MX_WDT - Watchdog timer
CONFIG_PIC32MX_T2 - Timer 2 (Timer 1 is the system time and always enabled)
CONFIG_PIC32MX_T3 - Timer 3
CONFIG_PIC32MX_T4 - Timer 4
CONFIG_PIC32MX_T5 - Timer 5
CONFIG_PIC32MX_IC1 - Input Capture 1
CONFIG_PIC32MX_IC2 - Input Capture 2
CONFIG_PIC32MX_IC3 - Input Capture 3
CONFIG_PIC32MX_IC4 - Input Capture 4
CONFIG_PIC32MX_IC5 - Input Capture 5
CONFIG_PIC32MX_OC1 - Output Compare 1
CONFIG_PIC32MX_OC2 - Output Compare 2
CONFIG_PIC32MX_OC3 - Output Compare 3
CONFIG_PIC32MX_OC4 - Output Compare 4
CONFIG_PIC32MX_OC5 - Output Compare 5
CONFIG_PIC32MX_I2C1 - I2C 1
CONFIG_PIC32MX_I2C2 - I2C 2
CONFIG_PIC32MX_SPI1 - SPI 1
CONFIG_PIC32MX_SPI2 - SPI 2
CONFIG_PIC32MX_UART1 - UART 1
CONFIG_PIC32MX_UART2 - UART 2
CONFIG_PIC32MX_ADC - ADC 1
CONFIG_PIC32MX_PMP - Parallel Master Port
CONFIG_PIC32MX_CM1 - Comparator 1
CONFIG_PIC32MX_CM2 - Comparator 2
CONFIG_PIC32MX_RTCC - Real-Time Clock and Calendar
CONFIG_PIC32MX_DMA - DMA
CONFIG_PIC32MX_FLASH - FLASH
CONFIG_PIC32MX_USBDEV - USB device
CONFIG_PIC32MX_USBHOST - USB host
PIC32MX Configuration Settings
DEVCFG0:
CONFIG_PIC32MX_DEBUGGER - Background Debugger Enable. Default 3 (disabled). The
value 2 enables.
CONFIG_PIC32MX_ICESEL - In-Circuit Emulator/Debugger Communication Channel Select
Default 1 (PG2)
CONFIG_PIC32MX_PROGFLASHWP - Program FLASH write protect. Default 0xff (disabled)
CONFIG_PIC32MX_BOOTFLASHWP - Default 1 (disabled)
CONFIG_PIC32MX_CODEWP - Default 1 (disabled)
DEVCFG1: (All settings determined by selections in board.h)
DEVCFG2: (All settings determined by selections in board.h)
DEVCFG3:
CONFIG_PIC32MX_USBIDO - USB USBID Selection. Default 1 if USB enabled
(USBID pin is controlled by the USB module), but 0 (GPIO) otherwise.
CONFIG_PIC32MX_VBUSIO - USB VBUSON Selection (Default 1 if USB enabled
(VBUSON pin is controlled by the USB module, but 0 (GPIO) otherwise.
CONFIG_PIC32MX_WDENABLE - Enabled watchdog on power up. Default 0 (watchdog
can be enabled later by software).
The priority of interrupts may be specified. The value ranage of
priority is 4-31. The default (16) will be used if these any of these
are undefined.
CONFIG_PIC32MX_CTPRIO - Core Timer Interrupt
CONFIG_PIC32MX_CS0PRIO - Core Software Interrupt 0
CONFIG_PIC32MX_CS1PRIO - Core Software Interrupt 1
CONFIG_PIC32MX_INT0PRIO - External Interrupt 0
CONFIG_PIC32MX_INT1PRIO - External Interrupt 1
CONFIG_PIC32MX_INT2PRIO - External Interrupt 2
CONFIG_PIC32MX_INT3PRIO - External Interrupt 3
CONFIG_PIC32MX_INT4PRIO - External Interrupt 4
CONFIG_PIC32MX_FSCMPRIO - Fail-Safe Clock Monitor
CONFIG_PIC32MX_T1PRIO - Timer 1 (System timer) priority
CONFIG_PIC32MX_T2PRIO - Timer 2 priority
CONFIG_PIC32MX_T3PRIO - Timer 3 priority
CONFIG_PIC32MX_T4PRIO - Timer 4 priority
CONFIG_PIC32MX_T5PRIO - Timer 5 priority
CONFIG_PIC32MX_IC1PRIO - Input Capture 1
CONFIG_PIC32MX_IC2PRIO - Input Capture 2
CONFIG_PIC32MX_IC3PRIO - Input Capture 3
CONFIG_PIC32MX_IC4PRIO - Input Capture 4
CONFIG_PIC32MX_IC5PRIO - Input Capture 5
CONFIG_PIC32MX_OC1PRIO - Output Compare 1
CONFIG_PIC32MX_OC2PRIO - Output Compare 2
CONFIG_PIC32MX_OC3PRIO - Output Compare 3
CONFIG_PIC32MX_OC4PRIO - Output Compare 4
CONFIG_PIC32MX_OC5PRIO - Output Compare 5
CONFIG_PIC32MX_I2C1PRIO - I2C 1
CONFIG_PIC32MX_I2C2PRIO - I2C 2
CONFIG_PIC32MX_SPI1PRIO - SPI 1
CONFIG_PIC32MX_SPI2PRIO - SPI 2
CONFIG_PIC32MX_UART1PRIO - UART 1
CONFIG_PIC32MX_UART2PRIO - UART 2
CONFIG_PIC32MX_CN - Input Change Interrupt
CONFIG_PIC32MX_ADCPRIO - ADC1 Convert Done
CONFIG_PIC32MX_PMPPRIO - Parallel Master Port
CONFIG_PIC32MX_CM1PRIO - Comparator 1
CONFIG_PIC32MX_CM2PRIO - Comparator 2
CONFIG_PIC32MX_FSCMPRIO - Fail-Safe Clock Monitor
CONFIG_PIC32MX_RTCCPRIO - Real-Time Clock and Calendar
CONFIG_PIC32MX_DMA0PRIO - DMA Channel 0
CONFIG_PIC32MX_DMA1PRIO - DMA Channel 1
CONFIG_PIC32MX_DMA2PRIO - DMA Channel 2
CONFIG_PIC32MX_DMA3PRIO - DMA Channel 3
CONFIG_PIC32MX_FCEPRIO - Flash Control Event
CONFIG_PIC32MX_USBPRIO - USB
PIC32MXx specific device driver settings
CONFIG_UARTn_SERIAL_CONSOLE - selects the UARTn for the
console and ttys0 (default is the UART0).
CONFIG_UARTn_RXBUFSIZE - Characters are buffered as received.
This specific the size of the receive buffer
CONFIG_UARTn_TXBUFSIZE - Characters are buffered before
being sent. This specific the size of the transmit buffer
CONFIG_UARTn_BAUD - The configure BAUD of the UART. Must be
CONFIG_UARTn_BITS - The number of bits. Must be either 7 or 8.
CONFIG_UARTn_PARTIY - 0=no parity, 1=odd parity, 2=even parity
CONFIG_UARTn_2STOP - Two stop bits
PIC32MXx USB Device Configuration
PIC32MXx USB Host Configuration (the PIC32MX does not support USB Host)
Configurations
==============
Each PIC32MX configuration is maintained in a sub-directory and can be
selected as follow:
tools/configure.sh ubw32:<subdir>
Where <subdir> is one of the following:
nsh:
This is the NuttShell (NSH) using the NSH startup logic at
apps/examples/nsh.
NOTES:
1. This configuration uses the mconf-based configuration tool. To
change this configurations using that tool, you should:
a. Build and install the kconfig-mconf tool. See nuttx/README.txt
see additional README.txt files in the NuttX tools repository.
b. Execute 'make menuconfig' in nuttx/ in order to start the
reconfiguration process.
2. Serial Output
The OS test produces all of its test output on the serial console.
This configuration has UART1 enabled as a serial console.
TX -- J4 pin 31: U1TX/RF8
RX -- J4 pin 30: U1RX/RF2
GND -- J4 pin 40: GND
Vcc -- J4 pin 39: 5V
3. USB Configurations
Several USB device configurations can be enabled and included
as NSH built-in built in functions.
All USB device configurations require the following basic setup in
your NuttX configuration file to enable USB device support:
CONFIG_USBDEV=y : Enable basic USB device support
CONFIG_PIC32MX_USBDEV=y : Enable PIC32 USB device support
system/cdcacm - The system/cdcacm program can be included as an
function by adding the following to the NuttX configuration file:
CONFIG_SYSTEM_CDCACM=y
and defining the following in your .config file:
CONFIG_CDCACM=y : Enable the CDCACM device
Reference in New Issue View Git Blame Copy Permalink