Difference between revisions of "FPGA registers access from Linux userspace"
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[[Category:FPGA]] | [[Category:FPGA]] | ||
| − | = fpgaregs = | + | == Introduction == |
| − | === | + | |
| − | + | There are '''two methods''' to access FPGA registers on APF*. | |
| + | |||
| + | * For '''APF9328, APF27 and APF51''' registers access are done with a memory bus (parallel). | ||
| + | * For '''APF6_SP''' registers access are done with PCIe | ||
| + | |||
| + | == Memory bus == | ||
| + | === fpgaregs === | ||
| + | ====Installation==== | ||
| + | If the fpgaregs package is not already installed on your APF (''/usr/bin/fpgaregs''), you can select it in the Buildroot menuconfig: | ||
<pre class="host"> | <pre class="host"> | ||
$ make menuconfig | $ make menuconfig | ||
| Line 18: | Line 26: | ||
</pre> | </pre> | ||
| − | + | Then reflash your rootfs or install it manually. | |
| − | + | ====Usage==== | |
| − | ====16 bits read==== | + | ''fpgaregs'' can be used to do read or write accesses (16 or 32 bits wide) to the FPGA, from Linux userspace/console. |
| + | |||
| + | =====16 bits read===== | ||
<pre class="apf"> | <pre class="apf"> | ||
# fpgaregs w <address> | # fpgaregs w <address> | ||
</pre> | </pre> | ||
| − | Where <address> is an address relative to FPGA's mapping in hexadecimal value. | + | Where <address> is an address relative to FPGA's mapping in hexadecimal value. Example: |
| + | <pre class="apf"> | ||
| + | # fpgaregs w 0 | ||
| + | </pre> | ||
| − | ====16 bits write==== | + | =====16 bits write===== |
<pre class="apf"> | <pre class="apf"> | ||
# fpgaregs w <address> <value> | # fpgaregs w <address> <value> | ||
| Line 36: | Line 49: | ||
Where <value> is hexadecimal value to write. | Where <value> is hexadecimal value to write. | ||
| − | ====32 bits read==== | + | =====32 bits read===== |
<pre class="apf"> | <pre class="apf"> | ||
# fpgaregs l <address> | # fpgaregs l <address> | ||
</pre> | </pre> | ||
| − | ====32 bits write==== | + | =====32 bits write===== |
<pre class="apf"> | <pre class="apf"> | ||
# fpgaregs l <address> <value> | # fpgaregs l <address> <value> | ||
</pre> | </pre> | ||
| − | == the mmap problem == | + | === the mmap problem === |
{{Note| This problem is corrected with latest Toolchains compilation options}} | {{Note| This problem is corrected with latest Toolchains compilation options}} | ||
| Line 62: | Line 75: | ||
<source lang="c"> | <source lang="c"> | ||
| + | void * ptr_fpga; | ||
ptr_fpga = mmap (0, 8192, PROT_READ|PROT_WRITE, MAP_SHARED, ffpga, FPGA_ADDRESS); | ptr_fpga = mmap (0, 8192, PROT_READ|PROT_WRITE, MAP_SHARED, ffpga, FPGA_ADDRESS); | ||
</source> | </source> | ||
| Line 88: | Line 102: | ||
</source> | </source> | ||
| − | === The problem === | + | ==== The problem ==== |
By default, if the specific ''arm920t'' target is not specified, ''arm-linux-gcc'' will try to generate compatible read/write for all ARM9 model when it access register in 16bits. Indeed it seems that not all ARM9 have 16bits read/write capabilities (''ldrh'' asm instruction). | By default, if the specific ''arm920t'' target is not specified, ''arm-linux-gcc'' will try to generate compatible read/write for all ARM9 model when it access register in 16bits. Indeed it seems that not all ARM9 have 16bits read/write capabilities (''ldrh'' asm instruction). | ||
| Line 94: | Line 108: | ||
As the interface between i.MXL and FPGA on APF9328 has no 8bits read/write capabilities, each 8 bits access is recognized by the FPGA as a 16bits access. So on each 16bits access of the i.MXL, FPGA will process two 16bits access instead of 1. That is a problem when accessing a FIFO for example. | As the interface between i.MXL and FPGA on APF9328 has no 8bits read/write capabilities, each 8 bits access is recognized by the FPGA as a 16bits access. So on each 16bits access of the i.MXL, FPGA will process two 16bits access instead of 1. That is a problem when accessing a FIFO for example. | ||
| − | To avoid this painful problem don't forget the ''-mcpu=arm920t'' option when compiling ''fpgaregs'' for APF9328. | + | To avoid this painful problem don't forget the ''-mcpu=arm920t'' option when compiling ''fpgaregs'' for APF9328 and ''-mcpu=arm926ej-s'' for APF27. |
| + | |||
| + | == PCIe == | ||
| + | |||
| + | On [[APF6_SP]] FPGA memory is accessed with PCIe, to read/write on FPGA space an example is available with [[Pci_debug | pci_debug]]. | ||
| + | |||
| + | === Pci_debug === | ||
| + | |||
| + | See [[Pci_debug | pci_debug]] page to know how to access PCIe address space with a command line tool. | ||
==Links== | ==Links== | ||
* http://sources.redhat.com/ml/crossgcc/2005-08/msg00120.html : Explanation of the problem. | * http://sources.redhat.com/ml/crossgcc/2005-08/msg00120.html : Explanation of the problem. | ||
Latest revision as of 09:59, 27 February 2017
Contents
Introduction
There are two methods to access FPGA registers on APF*.
- For APF9328, APF27 and APF51 registers access are done with a memory bus (parallel).
- For APF6_SP registers access are done with PCIe
Memory bus
fpgaregs
Installation
If the fpgaregs package is not already installed on your APF (/usr/bin/fpgaregs), you can select it in the Buildroot menuconfig:
$ make menuconfig
Package Selection for the target --->
[*] Hardware handling / blockdevices and filesystem maintenance --->
[*] fpgaregs
$ make
Then reflash your rootfs or install it manually.
Usage
fpgaregs can be used to do read or write accesses (16 or 32 bits wide) to the FPGA, from Linux userspace/console.
16 bits read
# fpgaregs w <address>
Where <address> is an address relative to FPGA's mapping in hexadecimal value. Example:
# fpgaregs w 0
16 bits write
# fpgaregs w <address> <value>
Where <value> is hexadecimal value to write.
32 bits read
# fpgaregs l <address>
32 bits write
# fpgaregs l <address> <value>
the mmap problem
 |
Note: This problem is corrected with latest Toolchains compilation options |
First of all, you need to get a file descriptor for /dev/mem using the open() function
ffpga=open("/dev/mem",O_RDWR|O_SYNC);
Now you have a valid file descriptor to access your FPGA.
The O_SYNC option is recommended to avoid Linux to cache the content of /dev/mem and delay any modification done in this file.
To access fpga register, fpgaregs use the mmap() system call :
void * ptr_fpga;
ptr_fpga = mmap (0, 8192, PROT_READ|PROT_WRITE, MAP_SHARED, ffpga, FPGA_ADDRESS);
Thanks to this function, fpga registers are accessible directly on memory with pointer ptr_fpga. To read and write in 16bits or in 32 bits we will cast the pointer value in unsigned short or unsigned int :
16bits write
*(unsigned short*)(ptr_fpga+(address)) = (unsigned short)value;
read
value = *(unsigned short*)(ptr_fpga+(address));
32 bits write
*(unsigned int*)(ptr_fpga+(address)) = (unsigned short)value;
read
value = *(unsigned int*)(ptr_fpga+(address));
The problem
By default, if the specific arm920t target is not specified, arm-linux-gcc will try to generate compatible read/write for all ARM9 model when it access register in 16bits. Indeed it seems that not all ARM9 have 16bits read/write capabilities (ldrh asm instruction).
As the interface between i.MXL and FPGA on APF9328 has no 8bits read/write capabilities, each 8 bits access is recognized by the FPGA as a 16bits access. So on each 16bits access of the i.MXL, FPGA will process two 16bits access instead of 1. That is a problem when accessing a FIFO for example.
To avoid this painful problem don't forget the -mcpu=arm920t option when compiling fpgaregs for APF9328 and -mcpu=arm926ej-s for APF27.
PCIe
On APF6_SP FPGA memory is accessed with PCIe, to read/write on FPGA space an example is available with pci_debug.
Pci_debug
See pci_debug page to know how to access PCIe address space with a command line tool.
Links
- http://sources.redhat.com/ml/crossgcc/2005-08/msg00120.html : Explanation of the problem.
