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suservo: add some more comments to the RTServoMem to clarify the RTIO interface (#1323)

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hartytp 2019-05-17 16:12:35 +01:00 committed by GitHub
parent d9fc2847c1
commit cfe1f56f73
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2 changed files with 26 additions and 4 deletions

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@ -25,7 +25,31 @@ class RTServoCtrl(Module):
class RTServoMem(Module):
"""All-channel all-profile coefficient and state RTIO control
interface."""
interface.
Servo internal addresses are internal_address_width wide, which is
typically longer than the 8-bit RIO address space. We pack the overflow
onto the RTIO data word after the data.
Servo address space (from LSB):
- IIR coefficient/state memory address, (w.profile + w.channel + 2) bits.
If the state memory is selected, the lower bits are used directly as
the memory address. If the coefficient memory is selected, the LSB
(high_coeff) selects between the upper and lower halves of the memory
location, which is two coefficients wide, with the remaining bits used
as the memory address.
- config_sel (1 bit)
- state_sel (1 bit)
- we (1 bit)
destination | config_sel | state_sel
----------------|------------|----------
IIR coeff mem | 0 | 0
IIR coeff mem | 1 | 0
IIR state mem | 0 | 1
config (write) | 1 | 1
status (read) | 1 | 1
"""
def __init__(self, w, servo):
m_coeff = servo.iir.m_coeff.get_port(write_capable=True,
mode=READ_FIRST,
@ -44,8 +68,6 @@ class RTServoMem(Module):
assert w.coeff >= w.word
# coeff, profile, channel, 2 mems, rw
# this exceeds the 8-bit RTIO address, so we move the extra ("overflow")
# address bits into data.
internal_address_width = 3 + w.profile + w.channel + 1 + 1
rtlink_address_width = min(8, internal_address_width)
overflow_address_width = internal_address_width - rtlink_address_width

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@ -127,7 +127,7 @@ class IIR(Module):
Each profile stores 8 values, each up to W.coeff bits wide, arranged as:
[FTW1, B1, POW, CFG, OFFSET, A1, FTW0, B0]
The lower 8 bits of CFG hold the ADC input channel index SEL.
The bits from bit 8 up hold the IIR activation delay DLY.
The subsequent 8 bits hold the IIR activation delay DLY.
The back memory is 2*W.coeff bits wide and each value pair
(even and odd address)
are stored in a single location with the odd address value occupying the