PrairieLearn OER Element: Cache Table

This element was developed by Geoffrey Herman. Please carefully test the element and understand its features and limitations before deploying it in a course. It is provided as-is and not officially maintained by PrairieLearn, so we can only provide limited support for any issues you encounter!

If you like this element, you can use it in your own PrairieLearn course by copying the contents of the elements folder into your own course repository. Note that this repository contains two separate elements that are designed to be used in combination, but can also be used independently. The repository also contains a cache-tables.py script in the serverFilesCourse folder that can be helpful for generating caches to use with the element. The provided example questions illustrate how to use the script.

pl-cache-table element

This element displays a cache table that students can modify. The dimensions of the cache are determined at minimum by the attributes set-bits (number of rows), num-ways (number of cache blocks per row, and presence of LRU FSMs). Optional attributes such block-bits, show-data, show-valid can add additional columns. The element has 3 grading modes: blocks (default), cells, and all-or-nothing. The cache comes with a reset button that allows students to reset the cache to the initial problem state.

The initial contents and final contents of the cache must be supplied to the element via data['params'][answers-name] and data['correct_answers'][answers-name] respectively where answers-name is the unique name given to the instance of the element via the html tag (i.e., answers-name would be cache in the example below (e.g., the inital cache state should be stored in data['params']['cache'])). A cache configuration must be an list where each element of the list is a dictionary that must contain a tags key, but can also have blocks, lru, and valid keys. tags, lru, and valid should be an list of strings, the length of the lists is the same as num-ways. blocks should be an list of lists, where the outer list has length num_ways and the inner lists have length 2**set-bits. The inner list should be a lists of strings. For example, a 3-way set associative cache with 2B blocks and 4 sets might look like

data['params']['cache'] = [
    {'tags': ['0x0', '0x1', '0x3'], 'lru': ['0', '1', '2'], 'blocks': [['3', '106'], ['168', '44'], ['75', '64']], 'valid': ['1', '1', '1']}, 
    {'tags': ['0x0', '0x2', '0x3'], 'lru': ['2', '1', '0'], 'blocks': [['38', '141'], ['38', '239'], ['252', '54']], 'valid': ['1', '1', '1']}, 
    {'tags': ['0x2', '0x3', '0x0'], 'lru': ['2', '1', '0'], 'blocks': [['138', '80'], ['114', '107'], ['16', '242']], 'valid': ['1', '1', '1']}, 
    {'tags': ['0x0', '0x2', '0x1'], 'lru': ['0', '1', '2'], 'blocks': [['228', '115'], ['109', '22'], ['173', '190']], 'valid': ['1', '1', '1']}
]

Example

<pl-cache-table 
    answers-name="cache"
    set-bits = "2"
    num-ways = "2"
    block-bits = "1"
></pl-cache-table>

Element Attributes

Attribute	Type	Description
answers-name	string (required)	Unique name for the element.
set-bits	integer (required)	Number of bits used to encode the cache sets. Creates 2**set-bits sets in the cache
num-ways	integer (required)	Set associativity of the cache.
block-bits	integer (default: 1)	Number of bits used to encode the number of Bytes per cache block. Creates 2**block-bits Bytes in each way of the cache.
show-data	boolean (default: true)	If set to true, data cells are displayed as a set of columns in each cache block.
show-valid	boolean (default: false)	If set to true, valid bits are displayed as a separate column in each block.
show-dirty	boolean (default: false)	If set to true, dirty cells are displayed as a set of columns in each cache block.
grade-mode	boolean (default: blocks)	If set to blocks, each cache block is graded as a unit. If one cell of a block is wrong, the whole cell is wrong. Students earn points for correctly updating blocks that changed and lose points for incorrectly updating blocks that should have stayed the same. If set to 'cells', each cell is graded individually. Students earn points for correctly updating each cell that changed and lose points for incorrectly updating cells that should have stayed the same. If set to all-or-nothing, students get 0% unless all cells are correct.
display-base	string (default: hex)	Must be hex or bin. Changes the display format of tag, index, and offset to be in hex or binary respectively.
show-partial-score	boolean (default: true)	Shows block-by-block feedback via highlighting in blocks or all-or-nothing grading mode and cell-by-cell feedback via highlighting in cells.
show-percentage-score	boolean (default: true)	Percentage score for the question is displayed as a badge.
is-material	boolean (default: false)	When false, cache is editable and submitted answer needs to match correct answer. When true, cache is not editable and will display cache data stored in data['params'][answers-name].
weight	integer (default: 1)	Weight to use when computing a weighted average score over elements.

pl-cache-access-table element

This element displays a table that lists a series of memory access that interact with a cache. Students are expected to determine which memory accesses result in a hit or a miss in the cache. The element expects a correct answer to be stored in data['correct_answers'] in a dictionary entry that shares the same answers_name. The dictionary entry should be a list of dictionary entries that include an address stored as a string and a hit/miss flag (hit).

data['correct_answers'][f'{answers_name}'] = [
    {'address': '0x1a', 'hit': False}, 
    {'address': '0x16', 'hit': False}, 
    {'address': '0x1f', 'hit': False}, 
    {'address': '0x1f', 'hit': True}
]

The element has 3 grading modes: through-first (default), all, and all-or-nothing. through-first is the default grading mode to discourage lazy guessing (i.e., under the all grading condition, students can get all answers correct on a second guess without reasoning about the problem).

Example

<pl-cache-access-table 
    answers-name="{{params.answers_name}}_access" 
></pl-cache-access-table>

Element Attributes

Attribute	Type	Description
answers-name	string (required)	Unique name for the element.
grade-mode	boolean (default: through-first)	If set to through-first, grading stops after the first mistake is encountered in the table and all remaining memory accesses are considered to be wrong. Students are not given feedback on later memory accesses. If set to all, each row is graded and feedback is available. For through-first and all the percentage score is the number of correct rows / number of rows. If set to all-or-nothing, each row is graded and feedback is available, but students get 0% unless all rows are correct.
show-partial-score	boolean (default: true)	Shows block-by-block feedback via highlighting in blocks or all-or-nothing grading mode and cell-by-cell feedback via highlighting in cells.
show-percentage-score	boolean (default: true)	Percentage score for the question is displayed as a badge.
empty-cache	boolean (default: 'false')	All cache blocks start as invalid, first access is a miss. Assert the first access is a miss with no radio button
weight	integer (default: 1)	Weight to use when computing a weighted average score over elements.