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add optional guard band to delay chain sizing

This commit is contained in:
Sam Crow 2023-07-05 16:08:38 -07:00
parent d65ccfcc95
commit 468c972acb
2 changed files with 13 additions and 4 deletions
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9
compiler/modules/control_logic_delay.py
View File

@ -142,21 +142,26 @@ class control_logic_delay(control_logic_base):
# time for bitline to drop from vdd by threshold voltage once wordline enabled
bitline_vth_swing = (spice["nom_supply_voltage"] - spice["nom_threshold"]) / spice["nom_supply_voltage"]
bitline_vth_delay = abs(math.log(1 - bitline_vth_swing)) * spice["wire_unit_r"] * bitline_area * bitline_cap_ff
print("delays: delay_stage {} precharge {} pen {} wl {} wlen {} vth {}".format(inverter_stage_delay, precharge_delay, pen_signal_delay, wordline_delay, wlen_signal_delay, bitline_vth_delay))
# print("delays: delay_stage {} precharge {} pen {} wl {} wlen {} vth {}".format(inverter_stage_delay, precharge_delay, pen_signal_delay, wordline_delay, wlen_signal_delay, bitline_vth_delay))
delays = [None] * 5
# keepout between p_en rising and wl_en falling
delays[0] = int((wlen_signal_delay + wordline_delay) / inverter_stage_delay) # could possibly subtract pen_signal_delay?
delays[0] = (wlen_signal_delay + wordline_delay) / inverter_stage_delay # could possibly subtract pen_signal_delay?
delays[0] = int(delays[0] * OPTS.delay_control_scaling_factor)
# round up to nearest even integer
delays[0] += delays[0] % 2
delays[2] = delays[0] + (pen_signal_delay + precharge_delay) / inverter_stage_delay
delays[2] *= OPTS.delay_control_scaling_factor
# round up to nearest odd integer
delays[2] = int(1 - (2 * ((1 - delays[2]) // 2)))
# delays[1] can be any even value less than delays[2]
delays[1] = delays[2] - 1
# keepout between p_en falling and wl_en rising
delays[3] = delays[2] + pen_signal_delay / inverter_stage_delay
delays[3] *= OPTS.delay_control_scaling_factor
delays[3] = int(1 - (2 * ((1 - delays[3]) // 2)))
delays[4] = delays[3] + (wlen_signal_delay + wordline_delay + bitline_vth_delay) / inverter_stage_delay
delays[4] *= OPTS.delay_control_scaling_factor
delays[4] = int(1 - (2 * ((1 - delays[4]) // 2)))
self.delay_chain_pinout_list = delays
# FIXME: fanout should be used to control delay chain height

8
compiler/options.py
View File

@ -67,9 +67,13 @@ class options(optparse.Values):
# Approximate percentage of delay compared to bitlines
rbl_delay_percentage = 0.5
# Allow manual adjustment of the delay chain over automatic
auto_delay_chain_sizing = False
# delay chain is automatically sized in delay based control logic
# this multiplier can be used to add a guard band to the standard timing
# lowering it can improve performance but may cause sram to fail
delay_control_scaling_factor = 1.0
# stages for delay chain in rbl control logic only
delay_chain_stages = 9
# fanout per stage for any control logic
delay_chain_fanout_per_stage = 4
accuracy_requirement = 0.75