mirror of
git://projects.qi-hardware.com/wernermisc.git
synced 2024-12-01 12:53:44 +02:00
64 lines
2.6 KiB
Plaintext
64 lines
2.6 KiB
Plaintext
|
jtag-boot (for Milkymist One)
|
||
|
|
=============================
|
||
|
|
|
||
|
|
This collection of scripts talks via JTAG to the FPGA of a Milkymist One.
|
||
|
|
It makes the FPGA load a bitstream (FPGA configuration) from NOR.
|
||
|
|
|
||
|
|
|
||
|
|
Elements involved
|
||
|
|
-----------------
|
||
|
|
|
||
|
|
The mkboot script generates a very short bitstream that instructs the
|
||
|
|
configuration subsystem of the FPGA to perform the boot operation.
|
||
|
|
|
||
|
|
A bitstream is a sequence of instructions for the configuration subsystem.
|
||
|
|
Bitstreams are used for various purposes, for example, the configuration
|
||
|
|
data of the FPGA is also contained in a (much larger) bitstream.
|
||
|
|
|
||
|
|
mkboot also adds the minimum set of headers of the ".bit" format to the
|
||
|
|
bitstream. This allows the bitstream to be transferred to the FPGA via
|
||
|
|
JTAG, using the UrJTAG utility.
|
||
|
|
|
||
|
|
UrJTAG is controlled via the boot.jtag script, which performs the basic
|
||
|
|
initialization of the JTAG system, defines a few chip-specific constants,
|
||
|
|
and then loads and executes the bitstream generated by mkboot.
|
||
|
|
|
||
|
|
|
||
|
|
Bitstream content and format
|
||
|
|
----------------------------
|
||
|
|
|
||
|
|
The bitstream instructs the configuration subsystem of the to erase the
|
||
|
|
present FPGA configuration, load a new one from NOR, and then let the
|
||
|
|
FPGA "run" it.
|
||
|
|
|
||
|
|
The structure of this kind of bitstream is described on Table 7-1 on page
|
||
|
|
126, section "IPROG Reconfiguration", of [1]. The format of the bitstream
|
||
|
|
is described in the section "Configuration packets" starting at page 88
|
||
|
|
of [1].
|
||
|
|
|
||
|
|
The NOR address from where the configuration bitstream will be loaded was
|
||
|
|
obtained from the M1 standby bitstream, starting around line 205 of [2].
|
||
|
|
|
||
|
|
Finally, the format of the .bit file was simply taken from the function
|
||
|
|
xlx_bitstream_load_bit of [3]. This is the same function in UrJTAG that
|
||
|
|
loads the file with the "pld load" command.
|
||
|
|
|
||
|
|
[1] Xilinx. "Spartan-6 FPGA Configuration User Guide"
|
||
|
|
http://www.xilinx.com/support/documentation/user_guides/ug380.pdf
|
||
|
|
[2] https://github.com/milkymist/milkymist/blob/master/boards/milkymist-one/standby/standby.v
|
||
|
|
[3] http://urjtag.git.sourceforge.net/git/gitweb.cgi?p=urjtag/urjtag;a=blob_plain;f=urjtag/src/pld/xilinx_bitstream.c;hb=HEAD
|
||
|
|
|
||
|
|
|
||
|
|
System state and behaviour
|
||
|
|
--------------------------
|
||
|
|
|
||
|
|
This process differs from a regular boot in that it should be able to
|
||
|
|
boot the FPGA into the "regular" bitstream (or the "rescue" bitstream)
|
||
|
|
from any state, including after a failed attempt to load the "standby"
|
||
|
|
bitstream.
|
||
|
|
|
||
|
|
The successful booting of FlickerNoise with jtag-boot does therefore not
|
||
|
|
mean that the M1 would be able to boot regularly. E.g., if the standby
|
||
|
|
bitstream is corrupted, the M1's FPGA initialization - without using
|
||
|
|
JTAG - would fail at this first step.
|