Narrow down by specifying conditions
現在1888件がヒットしています。check
こんにちは、ハチです。
Until last time, I have studied about the time to enter user mode, but I was not clear about the difference between Power On Reset ( POR ) and initialization.
This time, too, we will use the Cyclone® IV E as an example to study the differences.
I had the image of resetting the inside of the FPGA to "0", and I thought that initialization was to initialize the FPGA.
In addition, I have heard that in Altera's FPGA, initialization means assigning "0" to the flip-flop.
I had an image that POR is the start period after turning on the power, and initialization is the preparation period before entering user mode.
Power On Reset
A POR circuit is a circuit that keeps the entire device in reset until each supply voltage level stabilizes.
The power supplies being monitored are the following three power supplies.
●VCCINT
●VCCA
-VCCIO * Only I/O banks with configuration pins and JTAG pins are monitored
Note: Different device families have different power supply voltages monitored by the POR.
In other words, when the above three power supplies (VCCIN, VCCA, VCCIO (*)) meet the power supply specifications, the POR circuit releases the reset and configuration starts.
After power-on, during POR period, the device is in reset state, as shown in the table below.
|
pin |
Status |
|
nSTATUS |
Low |
|
CONF_DONE |
Low |
|
All user I/O |
トライステート状態 |
POR ends when each power supply voltage reaches the specified value, and configuration starts by releasing nSTATUS.
If you want to start configuration after a certain amount of time has passed after the power supply stabilizes (after POR ends), you can manually set nCONFIG to Low and then set nCONFIG to High when you want to start configuration. is.
お客様から下記のご質問をいただきました。
お客様: 「基板に電源投入後、FPGA よりも早く動き出すデバイスがあります。基板上では FPGA で結線されているので、FPGA のピンの状態を教えていただけないでしょうか？」
Come to think of it, I didn't know what the state of each pin of the FPGA was before configuration.
If the configuration is not completed, each pin will be in a state where it is not decided whether it is an input pin or an output pin.
Will all pins be in the same state?
When I checked the I/O status in each phase in the Cyclone® IV handbook, I found the following description.
(ハンドブックの記載はこちら⇒ Configuration -> Configuration -> Reset )
The I/O pins are tri-stated until the device enters user mode.
The user I/O pins and dual-purpose I/O pins have weak pull-up resistors, which are always enabled (after POR) before and during configuration. The weak pull up resistors are not enabled prior to POR.
User I/Os and Dual-Purpose I/Os (dual-purpose pins) must be tri-stated after POR until configuration is complete, and the device's internal Weak Pull-Up resistors must be enabled. I understand.
The resistance value of the I/O pull-up resistors present inside the device is specified in the datasheet and depends on the voltage level of VCCIO.
( Operating Condition -> DC Characteristics -> Internal Weak Pull-Up and Weak Pull-Down Resistor )
Power supply swings seem to cause POR to go wrong, resulting in configuration failures.
If the configuration fails, it seems that only the part related to the configuration will be analyzed, but I would like to check the voltage when the power is turned on.
イニシャライズ
Next, what kind of initialization is performed in the initialization?
As the name suggests, it initializes the device according to the logic state so that the designed logic can start operating.
Inside the device are the following and these primitives are set to the initial state of the design:
● LUT (lookup table)
● Register
●I/O
●Memory block
● Multiplier block
Summary
POR と イニシャライズの違いが理解できました。
●POR・・・電源投入時、電源電圧が規定値に達するまでデバイス全体をリセットしている
●イニシャライズ・・・FPGA 内部のレジスタ、メモリ等に初期値の設定をしている
As the customer asked, there shouldn't be a single FPGA on the board... So, the state of user I/O and dual-purpose pins when the FPGA is not in user mode was investigated, but the configuration How can a configuration pin act as a configuration pin and when is the configuration mode known?
We will investigate the next configuration sequence.
That was the difference between POR and Initialize! I said "configuration" in one word, but it's really deep...