Memory Card

Removable 128-kilobyte save memory on the Memory Card slots.

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Overview

The Memory Card is a device that keeps data after a reset or power off. The main unit has two connectors for it. A Multi tap connects more cards to one of them.¹ A card may be inserted or removed while the power is on.² The card shares the serial lines of the controller port, and the console addresses it with the byte 81h where a controller uses 01h. The byte exchange is otherwise the same as the controller protocol.³

Sony gives the following specifications:²

The memory is 128 Kbytes in 16 blocks of 8 Kbytes, and each block is 64 sectors of 128 bytes. The first block holds the directory and the other 15 blocks hold files.⁴ Those 15 blocks of 8 Kbytes are the 120 Kbytes that Sony lists as the capacity at format.² Sony made Memory Cards for the PlayStation only in this one size.⁵ The Memory Card file system page describes the directory block and the layout of a file.

BIOS Access

The BIOS provides the basic card services: the connection check, the logical format test and access in sectors of 128 bytes. So that controller reading and both connectors can be served together, the BIOS accesses a card on every second vertical blank and transfers one sector per access.⁶

The effective speed of the BIOS is well below the 10 Kbyte/sec that the card itself allows. Every vertical sync interrupt also clears the events of the HwCARD descriptor. Functions that wait for the vertical interrupt, such as VSync() of libgpu, can therefore miss a card event.^{2 6}

Card Events

The Memory Card library signals its results through events of two source descriptors:²

Card Presence and Format

A card holds a bit switch called the unconfirm flag. The flag is set when the card is inserted and cleared by _card_clear(), so it reveals that a card has been replaced.⁶ By default a card with the flag set cannot be read or written, and any attempt fails, so a program cannot write to the wrong card by mistake.⁷

Sony gives the following procedure for testing a card:⁶

1. Test for the card with _card_info(). An IOE event means that a card already confirmed is still present: go to step 5. A NEWCARD event means that a card not yet confirmed is present: go to step 2. A TIMOUT event means that no card is present. A communication error is also possible, so the test is retried.
2. Confirm the card with _card_clear(). A failure means that the card was removed or a communication error occurred. In that case return to step 1.
3. Test the logical format with _card_load(). An IOE event means that the card is formatted: go to step 5. A NEWCARD event means that it is not formatted: go to step 4. Otherwise return to step 1.
4. Format the card with format(). On success go to step 5, and otherwise return to step 1.
5. Perform input and output through the file system.

Sony requires that a program always ask the player before it formats a card, and never use automatic initialization.⁸

File System

The kernel reaches a card through the file system as the device bu:⁹

The size of a file is given in slots when the file is created and cannot be changed afterwards. When it creates a file, the file system joins any fragmented free space left by deleted files to provide the capacity.¹⁰ Sony's product catalog calls the slot a block.⁸

The bu device supports non-blocking access. When a file is opened with O_NOWAIT, read() and write() return as soon as the request is registered with the driver, and the end of the transfer is reported by an event.¹⁰

Sony fixes the first part of each file name. The product SLPS-00001 therefore gives file names that start with BISLPS-00001:⁸

The PlayStation does not check the region code.⁸

Multi Tap

On a Multi Tap each card is addressed as port number x 16 + card number, where the card number is 0 to 3:¹¹

At the byte level the slot is selected by the address byte, which becomes 8nh for slot n from 1 to 4.¹²

Read Command

A sector is read with command 52h ("R"). The sector number is 0 to 3FFh:¹³

(pre) means that the reply normally repeats the previous byte sent, and a reply in parentheses is not significant.¹⁴ For an invalid sector number a Sony card returns FFFFh as the confirmed number and ends the transfer without data. Third-party cards typically use the number AND 3FFh and send that sector, and some of them send eight 5Ch bytes after the end byte.¹³

Write Command

A sector is written with command 57h ("W"):¹⁵

Get ID Command

Command 53h ("S") is answered only by Sony cards. After the two ID and two acknowledge bytes the card returns 04h, 00h, 00h and 80h. psx-spx suggests that these may be the number of sectors (0400h) and the sector size (0080h), but their meaning is not confirmed.¹⁶

Any other command byte ends the transfer at once, or occasionally after one more byte that reads FFh.¹⁷

FLAG Byte

The FLAG byte is 08h at power on and whenever a card is inserted. Bit 3 shows that the directory has not been read yet, so it reveals a change of card, but it is cleared by a write and not by a read. Games therefore usually write a dummy sector to 003Fh to clear it, which wears that sector more than the others.¹⁸

Bit 2 appears to be intended for write errors. However, a write seems always to finish without setting it, and the error may instead appear in the FLAG of the next command. Some third-party cards also set bit 5.¹⁸

Timing

psx-spx reports that the card raises interrupt 7 about 1500 cycles after the first bit of each byte except the last. After the 7th byte of the read command a Sony card waits an extra 31000 cycles or so before the interrupt; cards from other makers do not.¹⁹ The write command shows no extra delay.¹⁹

References