[Request] A proposal for CSRs

[nmigen-issue-migration]

Issue by HarryHo90sHK
Friday Sep 27, 2019 at 07:10 GMT
Originally opened as m-labs/nmigen-soc#2

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#1 Following the general ideas discussed, I have made a new abstraction for CSR objects in my fork (HarryMakes/nmigen-soc@ba5f354 fixed). An example script is given below, which will print all the fields and their properties in a CSR named "test". You might also test the slicing functionality using the format mycsr[beginbit:endbit], but please note that the upper boundary is exclusive.

from nmigen import *

from nmigen_soc.csr import *

if __name__ == "__main__":
    mycsr = CSRGeneric("test", size=64, access=ACCESS_R_W, desc="A R/W test register")
    mycsr.f += CSRField("enable", desc="Enable signal", enums=['OFF', 'ON'])
    mycsr.f += CSRField("is_writing", size=2, access=ACCESS_R, desc="Status signal of writing or not",
                        enums=[
                              ("YES", 1),
                              ("NO", 0),
                              ("UNDEFINED", 2)
                        ])
    mycsr.f += CSRField("is_reading", size=2, access=ACCESS_R, desc="Status signal of reading or not")
    mycsr.f.is_reading.e += [
        ("UNDEFINED", 2),
        ("YES", 1),
        ("NO", 0)
    ]
    mycsr.f += CSRField("is_busy", size=2, access=ACCESS_R_WONCE, desc="Busy signal",
                        enums=[
                              ("YES", 1),
                              ("NO", 0),
                              ("UNKNOWN", -1)
                        ])
    mycsr.f += [
        CSRField("misc_a", size=32),
        CSRField("misc_b"),
        CSRField("misc_c")
    ]
    mycsr.f.misc_a.e += [
        ("HOT", 100000000),
        ("COLD", -100000000),
        ("NEUTRAL", 0)
    ]
    #mycsr.f += CSRField("impossible", size=30, startbit=6)

    print("{} (size={}) is {} : {}".format(
            mycsr.name, 
            mycsr.size,
            mycsr.access,
            mycsr.desc))
    for x in mycsr._fields:
        print("    {} [{},{}] (size={}) is {}{}".format(
            mycsr._fields[x].name, 
            mycsr._fields[x].startbit,
            mycsr._fields[x].endbit, 
            mycsr._fields[x].size,
            mycsr._fields[x].access,
            (" : "+mycsr._fields[x].desc if mycsr._fields[x].desc is not None else "")))

[nmigen-issue-migration]

Comment by HarryHo90sHK
Friday Sep 27, 2019 at 07:17 GMT

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For reference, here are the meanings of the access type Enums:

• ACCESS_R : Read-only
• ACCESS_W : Write-only
• ACCESS_R_W : Both read and write are allowed
• ACCESS_WONCE : Write-only, and only once per reset
• ACCESS_R_WONCE : Both read and write are allowed, but only one write is allowed per reset

Please also refer to: http://www.keil.com/pack/doc/CMSIS/SVD/html/elem_special.html#elem_access

[nmigen-issue-migration]

Comment by whitequark
Friday Sep 27, 2019 at 07:20 GMT

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Thanks, I'll take a look soon.

[nmigen-issue-migration]

Comment by whitequark
Wednesday Oct 16, 2019 at 15:52 GMT

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Thank you for the proposal. I have in mind some ways to simplify the code in your branch. I'm going to sketch out an implementation I have in mind, and then ask you for feedback to make sure I didn't miss anything important.

[jfng]

Superseded by #68.