> For the complete documentation index, see [llms.txt](https://calnix.gitbook.io/aave-book/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://calnix.gitbook.io/aave-book/functions/borrow/mint-debt-token.md).

# Mint debt token

## Overview

<figure><img src="/files/bOM7Wa0B8H5OSNJ1WaMd" alt=""><figcaption></figcaption></figure>

* [x] <mark style="color:orange;">cache</mark>
* [x] <mark style="color:orange;">updateState</mark>
* [x] getIsolationMode
* [x] validateBorrow
* [ ] mint debt token
* [ ] setBorrowing&#x20;
* [ ] update IsolationMode debt
* [ ] <mark style="color:orange;">updateInterestRates</mark>
* [ ] transfer underlying to user

<img src="/files/eOPuJQL0SCm6nXrBtWbU" alt="" class="gitbook-drawing">

* If stable interest was selected -> mint stable debt tokens&#x20;
* Else -> mint variable debt tokens

## mint stableDebtTokens

<figure><img src="/files/2kpw4UI5oHcDc1MZusTJ" alt=""><figcaption></figcaption></figure>

{% hint style="info" %}
rate: reserve.currentStableBorrowRate
{% endhint %}

### \_calculateBalanceIncrease

* For a user, calculates the increase in stable debt, due to interest accrued from timestamp of their last update, to current time.
* Serves to update user's prior stable debt

{% hint style="info" %}
`balanceIncrease` reflects interest accrued from lastUpdate till current block.timestamp.&#x20;

Does not relate to incoming borrow action.
{% endhint %}

### totalSupply

```solidity
    vars.previousSupply = totalSupply();
    vars.currentAvgStableRate = _avgStableRate;
    vars.nextSupply = _totalSupply = vars.previousSupply + amount;
```

#### vars.previousSupply = totalSupply();

`totalSupply` returns the updated supply value, by accounting for recently accrued interest, from `_totalSupplyTimestamp` till now, based on the `_avgStableRate`.

* `_avgStableRate`: internal storage variable on StableDebtToken.sol
* `previousSupply`: updated supply value

<figure><img src="/files/aH5xOi0hc2eupG9730dk" alt=""><figcaption></figcaption></figure>

* `principalSupply` => `super.totalSupply` calls `totalSupply` on `IncentivizedERC20` which returns `_totalSupply`

{% hint style="info" %}
`previousSupply` is set to `totalSupply()` instead of `_totalSupply` directly, so that the updated supply value can be obtained.&#x20;
{% endhint %}

With recent interest accounted for, the storage variable `_totalSupply` is updated with the incoming stable debt, `amount`.&#x20;

```solidity
vars.nextSupply = _totalSupply = 
    vars.previousSupply + amount;
```

### Calculate new stable rate

* `nextStableRate` is new stable rate, specific to the user

<figure><img src="/files/MxSPbrovmWry6kKkeXjh" alt=""><figcaption></figcaption></figure>

{% code overflow="wrap" %}

```solidity
nextStableRate = 
(_avgStableRate * currentBalance) + (amount * rate / currentBalance + amount)
```

{% endcode %}

* `nextStableRate` stored in the user's `UserState.additionalData` struct. `userState` mapping collects all users' `UserState` structs.
* Store update time in `_timestamps`.`_timestamps` mapping collects the last update timestamp for all users.
* Update the timestamp of the last update of  `_totalSupply.`

{% hint style="info" %}
rate: `reserve.currentStableBorrowRate`
{% endhint %}

### Update average Stable rate

* `_avgStableRate`: internal uint128 on StableDebtToken.sol
* `vars.currentAvgStableRate` was set to `_avgStableRate` at the start of `mint`

<figure><img src="/files/4ScYUjoTJobw7n9J3qyT" alt=""><figcaption></figcaption></figure>

{% code overflow="wrap" %}

```solidity
newAvgStableRate = 
(_avgStableRate * previousSupply) + [(rate * amountInRay) / nextSupply]
```

{% endcode %}

{% hint style="info" %}

* previousSupply: updated`totalSupply`
  {% endhint %}

### mint tokens

<figure><img src="/files/vLaOTQyW47kRxBrtUism" alt=""><figcaption></figcaption></figure>

Notice that we do not just mint as per the incoming stable debt amount; but also mint for `balanceIncrease`. This serves to update user's prior stable debt based on interest accrued over time elapsed since last update.

* Since we going to mint, mint to update the user's entire position

`mint` calls the internal function `_mint`:

<figure><img src="/files/z5hPAUmEDkpiVPzaB5Gr" alt=""><figcaption></figcaption></figure>

## mint variableDebtTokens

<figure><img src="/files/lMZx92SfVUqj89Qq7f2g" alt=""><figcaption></figcaption></figure>

* `amountScaled`: scale the borrow amount against variableBorrowIndex
* See variableDebtToken [mint](/aave-book/contracts/variabledebttoken.md#mint)


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://calnix.gitbook.io/aave-book/functions/borrow/mint-debt-token.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.