Currently CSR bus assumed that ~we means reading, that created
a problem that when for a CSR if reading has side effects and adr
parked unintentionally at that CSR, the reading side effect will be
triggered.
For SoCs, this happened when upstream bus issued a write transaction
with wishbone.sel, then on CSR bus it will be translated
as adr = addr, we = 0, which will be interpreted as a read to such
address, and trigger undesired side effect for such CSR.
Such upstream transaction will be generated by our bus width converter.
Given that we signal already presents in CSR Interface, the easiest way
to handle such situation is to generate re signal at bus bridges and
propagate it all the way down to the Interface.
Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
By default, location is still automatically determined but it's now possible to
specific locations:
The following module:
class MyModule(Module, AutoCSR):
def __init__(self):
self.csr0 = CSRStorage()
self.csr1 = CSRStorage(n=0)
self.csr2 = CSRStorage(n=2)
built on a SoC with 32-bit CSR data-width will have the following CSR mapping:
- 0x00 : csr1
- 0x04 : csr0
- 0x08 : reserved
- 0x0c : csr2
