Does Chisel support multiple clocks in a design, yet? If I wanted to implement an asynchronous fifo how would one going about doing that in Chisel?
Yes Chisel support multiple clocks in a design. If you want to use an asynchronous fifo you can import module ChiselUtil, it contain an asynchronous fifo :
https://github.com/ucb-bar/chisel/blob/master/src/main/scala/ChiselUtil.scala#L599
To change clock domain for a register, use the argument clock of Reg() :
val s1 = Reg(init = UInt(0), clock = clockB)
See more information in tutorial chapter 16.
Related
I am currently studying VHDL about SR Latch, and there comes to a part which I don't understand.
Can anyone explain What does ATTRIBUTE keep: boolean mean and what does it do in VHDL?
Thank you.
Warning heavy Xilinx bias...
The attributes for the VHDL are different for different tools and even change between versions of the same tools. The "keep" attribute for Xilinx used to insure that in the Vivado synthesis process the signal is not optimized away. It has been renamed recently to "syn_keep" to avoid confusion. I've used similar attributes to fix build issues before in which the tools make false assumptions.
NOTE: In order to avoid optimization during the implementation for Xilinx use "dont_touch".
Example:
A clock coming into the FPGA needs to be buffer through the Xilinx BUFG, but I needed the raw signal for a specific IP core. So I split the route, buffer the clock and fed the raw clock signal to the IP. The Vivado 2016.4 tool optimized out the unbuffered route creating a time constraint critical warnings and misbehavior on the hardware. The issue was found by tracing through the synthesis design schematics, observing the proper routing, and then viewing the implementation design schematic and seeing the route is altered. I fixed this by adding the dont_touch attribute to the unbuffered signal.
attribute dont_touch : boolean;
attribute clock_signal : string;
attribute dont_touch of clk_in : signal is true;
attribute clock_signal of clk_in : signal is "yes";
...
CLK_BUFG: component BUFG
port map (
I => clk_in,
O => buf_clk_in
);
It is a user defined attribute, thus not part of the VHDL standard itself. It is typically used to instruct the synthesis tool that it should keep a certain signal, for example being a flip-flop, even through the synthesis tool may determine that the signal can be removed during optimization.
For Altera Quartus synthesis tool, see this description: keep VHDL Synthesis Attribute
Hello this will be an experts questions :) You should be familiar with the following topics
Xilinx Multi-Gigabit-Transceivers (MGTs), especially the 7-Series GTX/GTH transceivers (GTXE2_CHANNEL)
Serial-ATA Gen1, Gen2 and Gen3, especially Out-of-Band (OOB) communication
Question:
How should a GTXE2 be configured for Serial-ATA?
OOB signaling is not working neither RX_ElectricalIdle nor ComInit.
Introduction:
I implemented a SATA controller for my final bachelor project, which supports multiple vendor/device platforms (Xilinx Virtex-5, Altera Stratix II, Altera Stratix IV). Now it's time to port this controller to the next device family: Xilinx 7-Series devices, by name a Kintex-7 on a KC705 board.
The SATA controller has a additional abstraction layer in the physical layer, which is based on SAPIS and PIPE 3.0. So to port the SATA controller to a new device family, I have only to write a new transceiver wrapper for a GTXE2 MGT.
As of Xilinx's CoreGenerator doesn't support the SATA protocols in the CoreGen wizard, I started a transceiver project from scratch and applied all necessary settings as far as they are asked by the wizard. After that I copied the GTXE2_COMMON instantiation into my wrapper module, ordered the generics and ports into a meaning full schema.
As a third step I connected all unconnected ports (the wizards doesn't assign all values !!) to their default values (the default from UG476 or zero if not defined).
In step 4 I checked all generics and ports again against the UG476 if they are compatible to the SATA settings. After that I connected my wrapper ports to the MGT and inserted cross-clock modules if necessary.
As of the KC705 board has no 150 MHz reference clock, I program the Si570 to supply this clock as "ProgUser_Clock" after each board "bootup". The MGT is in powerdown mode (P2) while this reconfiguration. When the Si570 is stable, the MGT is powered up, the used Channel PLL (CPLL) locks after ca. 6180 clock cycles. This CPLL_Locked events releases the GTX_TX|RX_Reset wires, which cause a GTX_TX|RX_ResetDone event after additional 270|1760 cycles (all cycles # 150 MHz -> 6,6 ns).
This behavior can be seen in chipscope, captured with a stable, uninterrupted auxiliary clock (200 MHz, slightly oversampled).
So the GXTE2 seams to be powered-up, operational and all clocks are stable.
GTXE2 ports to control the OOB signaling:
The MGT has several ports for OOB signaling. On TX these are:
TX_ElectricalIdle - forces TX into electrical idle condition
TX_ComInit - send a ComInit sequence
TX_ComWake - send a ComWake sequence
TX_ComFinish - sequence was send -> ready for next command
On RX:
RX_ElectricalIdle - RX_n/TX_p are in electrical idle condition (low-level interface)
RX_ComInit_Detected - a complete ComInit sequence was send
RX_ComWake_Detected - a complete ComWake sequence was send
Detailed error desciption:
TX sends no OOB sequences if TX_ComInit is high for one cycle.
RX_ElectricalIdle is always high
Tests:
SATA loopback cable: cut a SATA cable and solder the apropriate wires ;)
-- I'm using a special SFP to SATA adapter, which extends the KC705 with a SATA connector - http://shop.trioflex.ee/product.php?id_product=73
SMA loopback cables: I moved the MGT and connected the LVDS wires to the SMA jacks and installed 2 SMA cables as cross-over.
I programmed my old ML505 (Virtex-5) with onboard SATA connector to send ComInit sequences. The 2 boards are connected with a special SATA cross-over cable.
I connected a HDD with a partial stripped SATA cable to the KC705 (SFP2SATA adapter) and connected a 2.5 GSps scope (yes the signals are undersampled, but it's good to see bursts and idle periods...).
Experiences:
Test 3 shows transmitted OOB sequences from Virtex-5 to Kintex-7 but the ChipScope trigger event does not occur - Rx_ElectricalIdle is still high.
Test 4 shows no transmitted OOB sequences on the cable.
Should I post parts or the complete transceiver instanziation?
only the instance has ca. 650 lines :(
Please ask if you need more information, images, code, ... :)
Appendix:
Electrical idle means that the MGT drives both LVDS wires (TX_n/TX_p) with common mode voltage (V_cm) which is in range 0..2000 mV. If this condition is met, the common mode delta voltage is less than 100 mV, which is referred to as ElectricalIdle condition.
OOB-signaling means that the MGT transmits bursts of electrical idle and normal data symbols (D10.2 in 8b/10b notation) on the LVDS wires. SATA/SAS defines 3 OOB sequences call ComInit, ComWake, ComSAS which have different burst/idle durations. Host controllers and devices use these "Morse signals" to establish a link.
So I think I found some answers to the problem and want to share them.
I started to simulate the GTXE2_CHANNEL hardmacro. The simulation is behaving as "false" as the hardware. So I tried to simulate the MGT in Verilog and used an instance template from here:
http://forums.xilinx.com/t5/7-Series-FPGAs/Using-v7gtx-as-sata-host-PHY-and-there-is-issue-bout-ALIGN/td-p/374203
This template simulates ElectricalIDLE conditions and OOB sequences nearly correct. So I started to diff both solutions:
TXPDELECIDLEMODE, which is a port to choose the behavior of TXElectricalIDLE is not working as expected. So now I'm using the synchronous mode.
PCS_RSVD_ATTR is a unconstrained bit_vector generic of 48 bit. If you have a look into the wrapper code of the secureip GTXE2_CHANNEL component, you will find a conversion from bit_vector => std_logic_vector => string. Internally all generics are treated as DOWNTO ranged. So it's important to pass a DOWNTO constant to the GTXE2 generics!
So now you could ask why is he using to-ranged constants and generics?
Xilinx ISE up to the latest version 14.7 has a major bug in handling vectors of user defined types in unconstrained generics. The default direction of vectors is TO. If you are passing vectors of enums as DOWNTO to unconstrained generics into a component, ISE is reversing the vector elements and "emits" a TO ranged vector in the components !!
This is especially "funny" if the design hierarchy, which uses this generic, is not a balanced tree...
If you are using enums of 2 elements, the problem is not existent -> maybe this enum is mapped to a boolean.
Which task are still open?
TXComFinish is still not acknowledging the send OOB sequences.
I have to investigate this two bug fixes in synthesis and measure the OOB sequences with a scope - this may last some days :)
Edit 1:
Solution for Bug 1:
I have added a timeout counter whose timeout depends on the current generation (clock frequency) and the current COM sequence which is to be send. If the timeout is reached I generate my own TXComFinished signal. Don't or the timeout signal with the original TXComFinished signal from GTX, because sometimes this signal is high while COMWAKE is to be send, but this finished strobe belongs still to the previous COMRESET sequence!
Solution for an other Bug:
RXElectricalIDLE is not glitch free! To solve this problem I added an filter element on this wire, which suppresses spikes on that line.
So currently my controller is running at SATA Gen1 with 1.5 GHz on a KC705 board with a SFP2SATA adapter and I think this question is solved.
I'm using Spartan 3E starter kit. In creating a custom peripheral. I use the default settings except interfacing it to the PLB bus. I also generated XISE project. I added my ports which only consists of:
phy_tx_data : out std_logic_vector (0 to 3);
phy_tx_en : out std_logic;
phy_tx_clk : in std_logic;
phy_crs : in std_logic;
That is only but a few ports but the IOBs exceeded the limit of the available resources after synthesizing my ethernet transmit module. I would want to know how to actually implement it in the FPGA. Does the IOBs pertains to the ports of the top-level module? If so, I just added a few ports and it already exceeded. Why is that so? How can I overcome it? It seemed that the plb slave module consumed most of the available ports.. Or does the IOBs pertain to all signals and registers.. I really need help here.
IOB = physical IO pin. You can't put a design on an FPGA that requires more physical pins than the FPGA package provides. There are two solutions to this: either get a bigger FPGA or use fewer IO pins.
I am new to the Zedboard and am working up to transferring a complex hardware accelerator I currently have working on a regular FPGA board. Anyway I want to walk before I can run so have done the Zedboard speedway tutorials and am now toying around with small projects. My first of which being an simple adder accelerator:
-Send 2 numbers to the pl(programmable logic), to reg a and b
-the pl adds the numbers
-an interrupt to the PS(CPU) signals the computation has finished.
-In the ISR the PS reads the result from reg c
For this design I am using 3 registers (a,b,c) in the AXI interconnect, I have created the IP templates using CIP.
Basically though what is the best way send a control signal to enable the addition to the PL. So how should I signal to the PL adder that I have loaded the two numbers in reg a and b and now want to add them?
-Should I create a 1bit signal GPIO interconnect, add a 4th 1 bit control register to the IP? or is there a more 'stylish' way to do this by using the BUS2IPdata signals?
-Or is there another way to create custom PS to PL control enable signals?
Many thanks
Sam
Current idea:
-Build a switch in the user_logic HDL based on the BUS2IPWrCE, so when this is asserted to write to reg B I can then signal an enable signal to my adder? Or will I run into some concurrency issues with the data not being fully written straight away?
So to do this I have created the AXI perph using CIP, then modified the used_logic and two new ports, en and interrupt. Following these instructions I employed these external connections.http://www.programmableplanet.com/author.asp?section_id=2142&doc_id=264841
I then connected these two external connections to GPIO interfaces to provide the required functionality.
In your larger designs, it will be difficult to get performance using a GPIOs to control the scheduling of your accelerators. I suggest setting up FIFOs of command blocks between software and hardware.
For example, your peripheral could implement an AXI Stream slave, to receive commands from software, and an AXI Stream master, to send result indications back to software.
It can assert an interrupt to indicate that there are values in the response FIFO.
For higher performance, set up these FIFOs in DRAM and use AXI read/write masters in your peripheral.
There's a few questions in here, so bear with me, and thanks for taking the time to read this...
I recently wrote an SPI master, and have fully simulated it to make sure it works as expected.
From here I'd like to use it in another design where I've already got a 7 segment display component set up to take the value received from an ADC on the SPI bus, however I think I've confused myself with things at this point.
I need to send a pulse with other parameters to the SPI master to initiate a transfer, and wait on a busy signal to be de-asserted before I can send anything else. I'm not really sure how best way to implement the SPI master within the new design.
Would I use it in the design as a component? is there a better way?
If it has to be a component, is there any way I can set it up to directly output from that component to pins rather than me having to map to new inputs/outputs in the top level design?
For example, I have SCLK, MOSI, MISO, and CS; Can I not just have them output directly rather than having to be mapped through the top level? Seems like it'd simplify the top level and make it less clunky.
Also, would it be possible to set up a function to just say "Send this data over SPI and then return what's received"?
I'm still getting my head around how to put these things together so help/examples would be greatly appreciated. It seems like all the examples/tutorials available are based on things like using two half-adders, logic gates, etc. which only help to a point when they're so simple.
edit: Entity of my SPI Master
entity SPI_master is
generic(data_width: integer := 8;
clock_select: integer := 0);
port(SCLK: out std_logic;
MOSI: out std_logic;
MISO: in std_logic;
CS: out std_logic;
Mclk_in: in std_logic;
RST: in std_logic;
CPOL: in std_logic;
CPHA: in integer;
send_packet: in std_logic;
busy: out std_logic;
Tx_data: in std_logic_vector(data_width-1 downto 0);
Rx_data: out std_logic_vector(data_width-1 downto 0));
end SPI_master;
Your entity looks reasonable, though better names or comments on CPOL,CPHA would be useful!
Partial answers :
1) You CAN use it in your design as a component, but as previously mentioned, direct entity instantiation is simpler and less verbose.
2) No you can't directly output from deep in the hierarchy, and even if you could it would be a terrible idea!
Are you familiar with "Design Patterns" from C++, Ada or Java programming? If so, think of your top level design as the "Facade" pattern.
It's the only thing the external world needs to know about your design. And it will often be written as structural HDL, instantiating your other entities, and making interconnections between sub-units and connections to external ports.
There are ways to reduce the pain of these interconnections, especially across multiple layers of hierarchy, but ultimately you must break out the SPI signals to individual pins on the top level design, so that they can be connected to the correct wires on the PCB!
3) would it be possible to set up a function to just say "Send this data over SPI and then return what's received" ... not a function, no.
But certainly you can introduce a hardware wrapper to provide the rest of your design with a simple view of a complex task. For example, (assuming "send_packet" is asserted to write a byte on SPI, and "busy" goes high until the write is complete) you can create an entity taking an array of bytes and a "start" signal as inputs. Its architecture contains a process to count the bytes, outputting each in turn to SPI and waiting while "busy", and it can signal to its "caller" when done.