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base repository: GlasgowEmbedded/glasgow
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  • 2 commits
  • 2 files changed
  • 1 contributor

Commits on Jul 27, 2020

  1. applet.memory.prom: encourage (sic) metastability during reads. 

    This change is tested with Atmel AT29C flash and may or may not have
any effect on other memories. In case of this Atmel flash, output
buffers have parasitic feedback (likely through power supply) and
will oscillate if encouraged, e.g. if OE is kept asserted, or if data
transitions are maximized.
    @whitequark
    whitequark committed Jul 27, 2020
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    8b9bc15 View commit details

Commits on Jul 28, 2020

  1. database.microchip.avr: add ATmega{16,32}U4.

    @whitequark
    whitequark committed Jul 28, 2020
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    79d6716 View commit details
Showing with 9 additions and 1 deletion.
  1. +7 −1 software/glasgow/applet/memory/prom/__init__.py
  2. +2 −0 software/glasgow/database/microchip/avr.py
8 changes: 7 additions & 1 deletion software/glasgow/applet/memory/prom/__init__.py
View file
Original file line number Diff line number Diff line change
@@ -227,7 +227,12 @@ def elaborate(self, platform):

with m.State("READ-CYCLE"):
with m.If(timer == 0):
m.d.sync += bus.oe.eq(0)
# Normally, this would be the place to deassert OE. However, this would reduce
# metastability (during burst reads) in the output buffers of a memory that is
# reading bits close to the buffer threshold. Wait, isn't metastability bad?
# Normally yes, but this is a special case! Metastability causes unstable
# bits, and unstable bits reduce the chance that corrupt data will slip
# through undetected.
m.d.sync += dq_latch.eq(bus.q)
m.next = "READ-SEND"
with m.Else():
@@ -244,6 +249,7 @@ def elaborate(self, platform):
with m.State("WRITE-RECV"):
with m.If(dq_index == dq_bytes):
m.d.sync += bus.d.eq(dq_latch)
m.d.sync += bus.oe.eq(0) # see comment in READ-CYCLE
m.d.sync += bus.we.eq(1)
m.d.sync += timer.eq(write_cycle_cyc)
m.next = "WRITE-CYCLE"
2 changes: 2 additions & 0 deletions software/glasgow/database/microchip/avr.py
View file
Original file line number Diff line number Diff line change
@@ -41,6 +41,8 @@ def ATmega(name, signature, program_size, program_page, eeprom_size):
ATmega("168P", (0x1e, 0x94, 0x0b), program_size=16384, program_page=128, eeprom_size=512),
ATmega("328", (0x1e, 0x95, 0x14), program_size=32768, program_page=128, eeprom_size=1024),
ATmega("328P", (0x1e, 0x95, 0x0f), program_size=32768, program_page=128, eeprom_size=1024),
ATmega("16U4", (0x1e, 0x94, 0x88), program_size=16384, program_page=64, eeprom_size=4),
ATmega("32U4", (0x1e, 0x95, 0x87), program_size=16384, program_page=64, eeprom_size=4),
]

devices_by_signature = defaultdict(lambda: None,