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README.md
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# micropython_eeprom
MicroPython device driver for Microchip EEPROM chips (24LC512 and similar)
# 1. micropython_eeprom
A driver to enable MicroPython to access Microchip EEPROM devices. Unlike flash
memory EEPROMs may be written on a byte addressable basis. Its endurance is
specified as a million writes compared to the 10K typical of most flash memory.
In applications such as data logging the latter can be exceeded relatively
rapidly.
From one to eight chips may be used to construct a nonvolatile memory module
with sizes upto 512KiB. The driver allows the memory either to be mounted in
the target filesystem as a disk device or to be addressed as an array of bytes.
Where multiple chips are used, all must be the same size.
The work was inspired by [this one](https://github.com/dda/MicroPython.git).
This was written some five years ago. The driver in this repo employs some of
the subsequent improvements to MicroPython to achieve these advantages:
1. It supports multiple EEPROM chips to configure a single array.
2. Writes are up to 1000x faster by using ACK polling and page writes.
3. Page access improves the speed of multi-byte reads.
4. It is cross-platform.
5. The I2C bus can be shared with other chips.
6. It supports filesystem mounting.
7. Alternatively it can support byte-level access using Python slice syntax.
8. RAM allocations are reduced.
# 2. Connections
Any I2C interface may be used. The table below assumes a Pyboard running I2C(2)
as per the test program. To wire up a single EEPROM chip, connect to a Pyboard
as below. Pin numbers assume a PDIP package (8 pin plastic dual-in-line).
| EEPROM | PB |
|:------:|:---:|
| 1 A0 | Gnd |
| 2 A1 | Gnd |
| 3 A2 | Gnd |
| 4 Vss | Gnd |
| 5 Sda | Y10 |
| 6 Scl | Y9 |
| 7 WPA1 | Gnd |
| 8 Vcc | 3V3 |
For multiple chips the address lines A0, A1 and A2 of each chip need to be
wired to 3V3 in such a way as to give each device a unique address. These must
start at zero and be contiguous:
| Chip no. | A2 | A1 | A0 |
|:--------:|:---:|:---:|:---:|
| 0 | Gnd | Gnd | Gnd |
| 1 | Gnd | Gnd | 3V3 |
| 2 | Gnd | 3V3 | Gnd |
| 3 | Gnd | 3V3 | 3V3 |
| 4 | 3V3 | Gnd | Gnd |
| 5 | 3V3 | Gnd | 3V3 |
| 6 | 3V3 | 3V3 | Gnd |
| 7 | 3V3 | 3V3 | 3V3 |
Multiple chips should have 3V3, Gnd, SCL and SDA lines wired in parallel.
The I2C interface requires pullups, typically 3.3KΩ to 3.3V although any value
up to 10KΩ will suffice. The Pyboard 1.x has these on board. The Pyboard D has
them only on I2C(1). If you use a Pyboard D and power the EEPROMs from the 3V3
output you will need to enable the voltage rail by issuing:
```python
machine.Pin.board.EN_3V3.value(1)
```
Other platforms may vary. Even if boards have pullups connecting external
resistors will do no harm.
# 3. Files
1. `eeprom.py` Device driver.
2. `eep_test.py` Test programs for above.
# 4. The device driver
The driver supports mounting the EEPROM chips as a filesystem. Initially the
device will be unformatted so it is necessary to issue code along these lines to
format the device. Code assumes a 64KiB device:
```python
import uos
from machine import I2C
from eeprom import EEPROM, T24C512
eep = EEPROM(I2C(2), T24C512)
uos.VfsFat.mkfs(eep) # Omit this to mount an existing filesystem
vfs = uos.VfsFat(eep)
uos.mount(vfs,'/eeprom')
```
The above will reformat a drive with an existing filesystem: to mount an
existing filesystem simply omit the commented line.
Note that, at the outset, you need to decide whether to use the array as a
mounted filesystem or as a byte array. As a filesystem the limited size is an
issue, but a potential use case is for pickling Python objects for example to
achieve persistence when issuing `pyb.standby()`; also for holding a small
frequently updated persistent btree database.
The I2C bus must be instantiated using the `machine` module.
## 4.1 The EEPROM class
An `EEPROM` instance represents a logical EEPROM: this may consist of multiple
physical devices on a common I2C bus.
### 4.1.1 Constructor
This scans the I2C bus - if one or more correctly addressed chips are detected
an EEPROM array is instantiated. A `RuntimeError` will be raised if no device
is detected or if device address lines are not wired as described in
[Connections](./README.md#2-connections).
Arguments:
1. `i2c` Mandatory. An initialised master mode I2C bus.
2. `chip_size=T24C512` The chip size in bits. The module provides constants
`T24C64`, `T24C128`, `T24C256`, `T24C512` for the supported chip sizes.
3. `verbose=True` If True, the constructor issues information on the EEPROM
devices it has detected.
### 4.1.2 Methods providing byte level access
#### 4.1.2.1 `__getitem__` and `__setitem__`
These provides single byte or multi-byte access using slice notation. Example
of single byte access:
```python
from machine import I2C
from eeprom import EEPROM, T24C512
eep = EEPROM(I2C(1), T24C512)
eep[2000] = 42
print(eep[2000]) # Return an integer
```
It is also possible to use slice notation to read or write multiple bytes. If
writing, the size of the slice must match the length of the buffer:
```python
from machine import I2C
from eeprom import EEPROM, T24C512
eep = EEPROM(I2C(1), T24C512)
eep[2000:2002] = bytearray((42, 43))
print(eep[2000:2002]) # Returns a bytearray
```
Three argument slices are not supported: a third arg will be ignored.
#### 4.1.2.2 readwrite
This is a byte-level alternative to slice notation. It has the potential
advantage of using a pre-allocated buffer. Arguments:
1. `addr` Starting byte address
2. `buf` A `bytearray` or `bytes` instance containing data to write. In the
read case it must be a (mutable) `bytearray` to hold data read.
3. `read` If `True`, perform a read otherwise write. The size of the buffer
determines the quantity of data read or written. A `RuntimeError` will be
thrown if the read or write extends beyond the end of the physical space.
### 4.1.3 Methods providing the block protocol
For the protocol definition see
[the pyb documentation](http://docs.micropython.org/en/latest/library/uos.html#uos.AbstractBlockDev)
`readblocks()`
`writeblocks()`
`ioctl()`
### 4.1.4 Other methods
#### 4.1.4.1 The len() operator
The size of the EEPROM array in bytes may be retrieved by issuing `len(eep)`
where `eep` is the `EEPROM` instance.
#### 4.1.4.2 scan
Scans the I2C bus and returns the number of EEPROM devices detected.
Other than for debugging there is no need to call `scan()`: the constructor
will throw a `RuntimeError` if it fails to communicate with and correctly
identify the chip.
# 5. Test program eep_test.py
This assumes a Pyboard 1.x or Pyboard D with EEPROM(s) wired as above. It
provides the following.
## 5.1 test()
This performs a basic test of single and multi-byte access to chip 0. The test
reports how many chips can be accessed. Existing array data will be lost.
## 5.2 full_test()
Tests the entire array. Fills each 128 byte page with random data, reads it
back, and checks the outcome. Existing array data will be lost.
## 5.3 fstest(format=False)
If `True` is passed, formats the EEPROM array as a FAT filesystem and mounts
the device on `/eeprom`. If no arg is passed it simply the array and lists the
contents.
## 5.4 File copy
A rudimentary `cp(source, dest)` function is provided as a generic file copy
routine for setup and debugging purposes at the REPL. The first argument is the
full pathname to the source file. The second may be a full path to the
destination file or a directory specifier which must have a trailing '/'. If an
OSError is thrown (e.g. by the source file not existing or the EEPROM becoming
full) it is up to the caller to handle it. For example (assuming the EEPROM is
mounted on /eeprom):
```python
cp('/flash/main.py','/eeprom/')
```
See `upysh` in [micropython-lib](https://github.com/micropython/micropython-lib.git)
for other filesystem tools for use at the REPL.
# 6. ESP8266
Currently the ESP8266 does not support concurrent mounting of multiple
filesystems. Consequently the onboard flash must be unmounted (with
`uos.umount()`) before the EEPROM can be mounted.

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# eep_test.py MicroPython driver for Microchip EEPROM devices.
# Released under the MIT License (MIT). See LICENSE.
# Copyright (c) 2019 Peter Hinch
import uos
from machine import I2C, Pin
from eeprom import EEPROM, T24C512
# Return an EEPROM array. Adapt for platforms other than Pyboard or chips
# smaller than 64KiB.
def get_eep():
if uos.uname().machine.split(' ')[0][:4] == 'PYBD':
Pin.board.EN_3V3.value(1)
eep = EEPROM(I2C(2), T24C512)
print('Instantiated EEPROM')
return eep
# Dumb file copy utility to help with managing EEPROM contents at the REPL.
def cp(source, dest):
if dest.endswith('/'): # minimal way to allow
dest = ''.join((dest, source.split('/')[-1])) # cp /sd/file /eeprom/
with open(source, 'rb') as infile: # Caller should handle any OSError
with open(dest,'wb') as outfile: # e.g file not found
while True:
buf = infile.read(100)
outfile.write(buf)
if len(buf) < 100:
break
def test():
eep = get_eep()
sa = 1000
for v in range(256):
eep[sa + v] = v
for v in range(256):
if eep[sa + v] != v:
print('Fail at address {} data {} should be {}'.format(sa + v, eep[sa + v], v))
break
else:
print('Test of byte addressing passed')
data = uos.urandom(30)
sa = 2000
eep[sa:sa + 30] = data
if eep[sa:sa + 30] == data:
print('Test of slice readback passed')
def fstest(format=False):
eep = get_eep()
if format:
uos.VfsFat.mkfs(eep)
vfs=uos.VfsFat(eep)
try:
uos.mount(vfs,'/eeprom')
except OSError: # Already mounted
pass
print('Contents of "/": {}'.format(uos.listdir('/')))
print('Contents of "/eeprom": {}'.format(uos.listdir('/eeprom')))
print(uos.statvfs('/eeprom'))
def full_test():
eep = get_eep()
page = 0
for sa in range(0, len(eep), 128):
data = uos.urandom(128)
eep[sa:sa + 128] = data
if eep[sa:sa + 128] == data:
print('Page {} passed'.format(page))
else:
print('Page {} readback failed.'.format(page))
page += 1

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# eeprom.py MicroPython driver for Microchip EEPROM devices.
# Released under the MIT License (MIT). See LICENSE.
# Copyright (c) 2019 Peter Hinch
import time
from micropython import const
ADDR = const(0x50) # Base address of chip
T24C512 = const(65536) # 64KiB 512Kbits
T24C256 = const(32768) # 32KiB 256Kbits
T24C128 = const(16384) # 16KiB 128Kbits
T24C64 = const(8192) # 8KiB 64Kbits
# Logical EEPROM device consists of 1-8 physical chips. Chips must all be the
# same size, and must have contiguous addresses starting from 0x50.
class EEPROM():
def __init__(self, i2c, chip_size=T24C512, verbose=True):
self._i2c = i2c
if chip_size not in (T24C64, T24C128, T24C256, T24C512):
raise RuntimeError('Invalid chip size', chip_size)
nchips = self.scan(verbose, chip_size) # No. of EEPROM chips
self._c_bytes = chip_size # Size of chip in bytes
self._a_bytes = chip_size * nchips # Size of array
self._i2c_addr = 0 # I2C address of current chip
self._buf1 = bytearray(1)
self._addrbuf = bytearray(2) # Memory offset into current chip
# Check for a valid hardware configuration
def scan(self, verbose, chip_size):
devices = self._i2c.scan() # All devices on I2C bus
eeproms = [d for d in devices if ADDR <= d < ADDR + 8] # EEPROM chips
nchips = len(eeproms)
if nchips == 0:
raise RuntimeError('EEPROM not found.')
if min(eeproms) != ADDR or (max(eeproms) - ADDR + 1) > nchips:
raise RuntimeError('Non-contiguous chip addresses', eeproms)
if verbose:
s = '{} chips detected. Total EEPROM size {}bytes.'
print(s.format(nchips, chip_size * nchips))
return nchips
def __len__(self):
return self._a_bytes
def _wait_rdy(self): # After a write, wait for device to become ready
self._buf1[0] = 0
while True:
try:
if self._i2c.writeto(self._i2c_addr, self._buf1): # Poll ACK
break
except OSError:
pass
finally:
time.sleep_ms(1)
def __setitem__(self, addr, value):
if isinstance(addr, slice):
try:
if len(value) == (addr.stop - addr.start):
return self.readwrite(addr.start, value, False)
else:
raise RuntimeError('Slice must have same length as data')
except TypeError:
raise RuntimeError('Can only assign bytes/bytearray to a slice')
self._buf1[0] = value
self._getaddr(addr, 1)
self._i2c.writevto(self._i2c_addr, (self._addrbuf, self._buf1))
self._wait_rdy() # Wait for write to complete
def __getitem__(self, addr):
if isinstance(addr, slice):
buf = bytearray(addr.stop - addr.start)
return self.readwrite(addr.start, buf, True)
self._getaddr(addr, 1)
self._i2c.writeto(self._i2c_addr, self._addrbuf)
self._i2c.readfrom_into(self._i2c_addr, self._buf1)
return self._buf1[0]
# Given an address, set ._i2c_addr and ._addrbuf and return the number of
# bytes that can be processed in the current page
def _getaddr(self, addr, nbytes): # Set up _addrbuf and _i2c_addr
if addr >= self._a_bytes:
raise RuntimeError("EEPROM Address is out of range")
ca, la = divmod(addr, self._c_bytes) # ca == chip no, la == offset into chip
self._addrbuf[0] = (la >> 8) & 0xff
self._addrbuf[1] = la & 0xff
self._i2c_addr = ADDR + ca
pe = (addr & ~0x7f) + 0x80 # byte 0 of next page
return min(nbytes, pe - la)
# Read or write multiple bytes at an arbitrary address
def readwrite(self, addr, buf, read):
nbytes = len(buf)
mvb = memoryview(buf)
start = 0
while nbytes > 0:
npage = self._getaddr(addr, nbytes) # No. of bytes in current page
assert npage > 0
if read:
self._i2c.writeto(self._i2c_addr, self._addrbuf)
self._i2c.readfrom_into(self._i2c_addr, mvb[start : start + npage])
else:
self._i2c.writevto(self._i2c_addr, (self._addrbuf, buf[start: start + npage]))
self._wait_rdy()
nbytes -= npage
start += npage
addr += npage
return buf
# IOCTL protocol. Emulate block size of 512 bytes for now.
def readblocks(self, blocknum, buf):
return self.readwrite(blocknum << 9, buf, True)
def writeblocks(self, blocknum, buf):
self.readwrite(blocknum << 9, buf, False)
def ioctl(self, op, arg):
#print("ioctl(%d, %r)" % (op, arg))
if op == 4: # BP_IOCTL_SEC_COUNT
return self._a_bytes >> 9
if op == 5: # BP_IOCTL_SEC_SIZE
return 512