Savings Rate
. It allows users to deposit dotBTC and activate the dotBTCSavings Rate and earning savings on their dotBTC. The DSR is set by ABM Governance, and will typically be less than the base stability fee to remain sustainable. The purpose of Pot is to offer another incentive for holding dotBTC .mul(uint, uint)
, rmul(uint, uint)
, add(uint, uint)
& sub(uint, uint)
- will revert on overflow or underflowrpow(uint x, uint n, uint base)
, used for exponentiation in drip
, is a fixed-point arithmetic function that raises x
to the power n
. It is implemented in assembly as a repeated squaring algorithm. x
(and the result) are to be interpreted as fixed-point integers with scaling factor base
. For example, if base == 100
, this specifies two decimal digits of precision and the normal decimal value 2.1 would be represented as 210; rpow(210, 2, 100)
should return 441 (the two-decimal digit fixed-point representation of 2.1^2 = 4.41). In the current implementation, 10^27 is passed for base
, making x
and the rpow
result both of type ray
in standard MCD fixed-point terminology. rpow
’s formal invariants include “no overflow” as well as constraints on gas usage.wards
are allowed to call protected functions (Administration)pie
- stores the address' Pot
balance.Pie
- stores the total balance in the Pot
.dsr
- the dotBTC savings rate
. It starts as 1
(ONE = 10^27
), but can be updated by governance.chi
- the rate accumulator. This is the always increasing value which decides how much dotBTC - given when drip()
is called.vat
- an address that conforms to a VatLike
interface. It is set during the constructor and cannot be changed.vow
- an address that conforms to a VowLike
interface. Not set in constructor. Must be set by governance.rho
- the last time that drip is called.dsr
and vow
can be changed by an authorized address in the contract (i.e. ABM Governance). The values of chi
, pie
, Pie
, and rho
are updated internally in the contract and cannot be changed manually.chi
and pulls dotBTC from the vow
(by increasing the Vow
's Sin
).exit()
function.join
s and it is in their interest to call it again before they exit
, but there isn't a set rule for how often drip is called.uint wad
this parameter is based on the amount of dotBTC (since wad
= dotBTC / chi
) that you want to join
to the pot
. The wad * chi
must be present in the vat
and owned by the msg.sender
.msg.sender
's pie
amount is updated to include the wad
.Pie
amount is also updated to include the wad
.exit()
essentially functions as the exact opposite of join()
.uint wad
this parameter is based on the amount of dotBTC that you want to exit
the pot
. The wad * chi
must be present in the vat
and owned by the pot
and must be less than msg.sender
's pie
balance.msg.senders
pie
amount is updated by subtracting the wad
.Pie
amount is also updated by subtracting the wad
.Pot
:file(bytes32, uint256)
)file(bytes32, address)
)addresses
to store their dotBTC in the pot
to accumulate interest over timedsr
is set (globally) through the governance system. It can be set to any number > 0%. This includes the possibility of it being set to a number that would cause the DSR to accumulate faster than the collective Stability Fees, thereby accruing system debt and eventually causing MKR to be minted.drip()
has not been called recently before an address calls exit()
they will not get the full amount they have earned over the time of their deposit.join
or exit
1 dotBTC into/from the Pot, they should send a wad
= to 1 / chi
as the amount moved from their balance will be 1 * chi
(for an example of this, see DSS-Proxy-ActionsPot
could lead to locking of dotBTC if the exit()
function or the underlying vat.suck()
or vat.move()
functions were to have bugs.dsr
rate initially can be set through the Chief. Governance will be able to change the DSR based on the rules that the DS-Chief employs (which would include a Pause for actions).dsr
to an extremely high rate, this could cause the system's fees to be far too high. Furthermore, if governance allows the dsr
to (significantly) exceed the system fees, it would cause debt to accrue and increase the Flop auctions.