Sometimes a master needs to stop the flow of acks.

If you use a PLL locked signal for reset, synchronous reset does
not work. That's b/c the clock doesn't run while reset is asserted.

One shouldn't do that, but sometimes it is convenient when testing.

Peter Jansweijer authored 11 years ago and Grzegorz Daniluk committed 10 years ago

The simulator is crashing at the end of the LM32 startup code when it tries to
access the highest RAM location (at the stack pointer). After this access, the
LM32 verilog code already increments the address to be prepared for the next
cycle, which will never actually happen because you are at the end of the RAM.
It is this address increment in verilog that is one address outside the defined
RAM array for which the simulator complains and terminates. The actual
synthesized code is perfectly fine; no accesses outside RAM.

Peter Jansweijer authored 11 years ago and Grzegorz Daniluk committed 10 years ago

Tried in real hardware and this works better.

FIFO counters to other clock domain. Allows to constrain the maximum sync chain delay in a single UCF line.

gc_sync_register is a multibit cross-clock domain synchronizer, with constrainable input delay, to
prevent sync delays with more than 1 clock cycle uncertainity. Used to synchronize counters
in dual-clock FIFOs.

For Xilinx devices, add this constraint to your UCF file

NET "*/gc_sync_register_in[*]" MAXDELAY=<faster_clock_period / 2 here>;

Now wb_spi has generic parameters to configure registers length and number of
spi slaves. Reason for that is to keep default configuration in the repository
but also allow to adjust settings for WR Switch synthesis (and save resources).

The values used in WR Switch software fit in 8-bit registers so using 16-bits
in HDL was waste of resources.

Commit adds new WB register(IFS) that selects to which I2C interface master
should talk to. All other interfaces are then hold in idle state. IFS contains
also BUSY bit that is written only by host and marks that I2C Master is
currently in use and cannot be switched to another I2C interface. Host must
clear BUSY flag after the interaction with I2C interface is finished.

Even when g_num_pins was a small number, the registers inside were 32-bits, e.g. for g_num_pins=1 the module utilized 65 slice registers.

This is done to better reflect the interface of the module (structured Wishbone).
The documentation of the module is also changed in this respect.

If a very fast WB master queues a single-byte SPI command followed
immediately by the execute instruction, the SPI command will use
the old data in the FIFO. This delays execution by 1 cycle.

It was causing the simulation to fail with designs containing a xwb_register_link component.

the sdb address of the wb crossbar. The sdb address
is store in a CSR, 0xb, and it can be retrieved from the
firmware using an asm macro call.

Use a counter instead of a shift register + comparator.

It is based on gc_glitch_filt, but with the glitch filter length
dynamically progammable via a port.

Using the volatile configuration register to configure a flash chip
is a bad idea. The problem is that if the FPGA is reset, the flash
may be in a state inconsistent with what the FPGA requires to boot.

The correct solution is to configure the non-volatile configuration
register on the chip to what the FPGA expects on power-on. Then use
these same settings inside the flash core.

Going this route makes it necessary for software to be able to set
the non-volatile configuration register. Rather than making the core
even more complicated than it is, I have elected to add a FIFO which
software can fill to issue custom SPI commands. Since erase can only
be done from software anyway, I removed this code and let erase use
the custom command FIFO.

Comparing std_logic <= '0' seems to work!
However, it is certainly not what the author intended.

Signed-off-by: Theodor Stana <t.stana@cern.ch>