BIOS A Functions
Kernel functions called through address 0xA0 with the function number in R9.
| Vector | 0x000000A0 |
|---|---|
| Number register | R9 |
| Jump table | 0x00000200 |
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Overview
The A functions are called by loading the function number into R9 and jumping to address 0xA0. The four instructions at 0xA0 jump through the A function table at 0x00000200, which is 0x300 bytes long.12 Arguments go in R4 to R7 and on the stack, and the return value is in R2. The BIOS page describes the calling convention.1
Most A functions run from uncached ROM through an 8-bit bus. The memory and string functions also process data byte by byte. Consequently they are slow, and memcpy() takes about 160 cycles per byte while bzero() takes about 105.3
Several A functions duplicate B functions. A(00h) to A(09h) and A(3Bh) to A(3Eh) jump to the same code as B(32h) to B(3Fh); the boot code copies those addresses into the A table with AdjustA0Table().4 Functions A(A0h) to A(B4h) do not exist in the DTL-H2000 BIOS, and A(AFh) to A(B4h) do not exist in the CEX-1000 kernel.1
File Functions
These functions give low-level access to files and logical devices. They are described on the file I/O page.56
| Number | Function | Explanation |
|---|---|---|
| A(00h) | open(filename, accessmode) | Opens a file and returns its descriptor, or -17 |
| A(01h) | lseek(fd, offset, seektype) | Moves the file pointer from the start (0) or the current position (1)8 |
| A(02h) | read(fd, dst, length) | Reads length bytes and returns the number read, or -19 |
| A(03h) | write(fd, src, length) | Writes length bytes and returns the number written, or -110 |
| A(04h) | close(fd) | Closes the file and returns fd, or -111 |
| A(05h) | ioctl(fd, cmd, arg) | Executes a device control command (used only for TTY)12 |
| A(06h) | exit(exitcode) | Terminates the program and returns to the BIOS |
| A(07h) | isatty(fd) | Returns bit 1 of the device flags (set only for the DUART TTY) |
| A(08h) | getc(fd) | Reads one byte (sign-extended) |
| A(09h) | putc(char, fd) | Writes one byte (fd is the second argument) |
Conversion Functions
These functions convert between strings, characters and numbers.13 All of them use signed 32-bit values for both int and long.
| Number | Function | Explanation |
|---|---|---|
| A(0Ah) | todigit(char) | Returns 0 to 9 for "0" to "9" and 10 to 35 for letters |
| A(0Bh) | atof(src) | Does not work: uses the absent COP1 floating point unit |
| A(0Ch) | strtoul(src, src_end, base) | Converts an unsigned number |
| A(0Dh) | strtol(src, src_end, base) | Converts a signed number, with 0b, 0x and o prefixes |
| A(0Eh) | abs(val) | Returns the absolute value |
| A(0Fh) | labs(val) | Same as abs |
| A(10h) | atoi(src) | Converts a decimal number (a leading 0 selects octal) |
| A(11h) | atol(src) | Same as atoi |
| A(12h) | atob(src, num_dst) | Calls strtol with base 10 and exchanges the two results |
| A(25h) | toupper(char) | Converts a letter to uppercase |
| A(26h) | tolower(char) | Converts a letter to lowercase |
| A(32h) | strtod(src, src_end) | Does not work: uses the absent COP1 floating point unit |
atof() and strtod() were compiled for a MIPS processor with a COP1 floating point unit. The PlayStation has no such unit, and the BIOS does not emulate it. Calling either function therefore raises a coprocessor exception and stops the PlayStation in A(40h) SystemErrorUnresolvedException().13
Non-local Jumps
| Number | Function | Explanation |
|---|---|---|
| A(13h) | setjmp(buf) | Saves RA, SP, FP, R16 to R23 and GP in a 0x30-byte buffer and returns 014 |
| A(14h) | longjmp(buf, param) | Restores the registers from buf and returns param at the saved RA |
The buffer layout is RA at 0x00, SP at 0x04, FP at 0x08, R16 to R23 at 0x0C and GP at 0x2C. setjmp() does not save the COP0 or GTE state, and longjmp() does not change a param of 0 into 1, so the caller must pass a nonzero value.14 The same buffer format is used by HookEntryInt().15
String Functions
These functions follow the standard C library.16 Most of them refuse a null pointer and return 0 in that case.
| Number | Function | Explanation |
|---|---|---|
| A(15h) | strcat(dst, src) | Appends src to dst |
| A(16h) | strncat(dst, src, maxlen) | Appends at most maxlen characters |
| A(17h) | strcmp(str1, str2) | Compares two strings |
| A(18h) | strncmp(str1, str2, maxlen) | Compares at most maxlen characters |
| A(19h) | strcpy(dst, src) | Copies src to dst |
| A(1Ah) | strncpy(dst, src, maxlen) | Copies at most maxlen characters and pads with 0 |
| A(1Bh) | strlen(src) | Returns the string length |
| A(1Ch) | index(src, char) | Returns the address of the first occurrence of char |
| A(1Dh) | rindex(src, char) | Returns the address of the last occurrence of char |
| A(1Eh) | strchr(src, char) | Same as index |
| A(1Fh) | strrchr(src, char) | Same as rindex |
| A(20h) | strpbrk(src, list) | Finds the first character contained in list |
| A(21h) | strspn(src, list) | Returns the index of the first character of src in list |
| A(22h) | strcspn(src, list) | Returns the index of the first character of src not in list |
| A(23h) | strtok(src, list) | Splits a string at the separators in list; later calls pass 0 |
| A(24h) | strstr(str, substr) | Finds substr in str (misses some overlapping matches) |
strtok() copies the string into a 0x100-byte buffer in the kernel variables. A longer string than 255 characters therefore overwrites other kernel variables.16
Memory Functions
| Number | Function | Explanation |
|---|---|---|
| A(27h) | bcopy(src, dst, len) | Copies len bytes (src first) |
| A(28h) | bzero(dst, len) | Fills len bytes with 0 |
| A(29h) | bcmp(ptr1, ptr2, len) | Compares len bytes (same faults as memcmp) |
| A(2Ah) | memcpy(dst, src, len) | Copies len bytes and returns dst |
| A(2Bh) | memset(dst, fillbyte, len) | Fills len bytes and returns dst |
| A(2Ch) | memmove(dst, src, len) | Copies overlapping areas (copies one byte too many backwards) |
| A(2Dh) | memcmp(src1, src2, len) | Compares len bytes (returns the difference of the following byte) |
| A(2Eh) | memchr(src, scanbyte, len) | Returns the address of the first scanbyte, or 0 |
These functions refuse a destination of 0x00000000 and a length above 0x7FFFFFFF.3 memcmp() and bcmp() return the difference between the bytes after the first mismatch, so a return value of 0 does not prove that the blocks are equal.3
Utility and Heap Functions
The heap functions manage the area given to InitHeap(). The kernel does not initialize the heap, so malloc() fails until InitHeap() has been called.1718
| Number | Function | Explanation |
|---|---|---|
| A(2Fh) | rand() | Returns a 15-bit random number |
| A(30h) | srand(seed) | Sets the 32-bit random seed |
| A(31h) | qsort(base, nel, width, callback) | Sorts an array (uses the heap) |
| A(33h) | malloc(size) | Allocates a block, 4-byte aligned |
| A(34h) | free(buf) | Releases a block (no error check) |
| A(35h) | lsearch(key, base, nel, width, callback) | Linear search of an array |
| A(36h) | bsearch(key, base, nel, width, callback) | Binary search of a sorted array |
| A(37h) | calloc(sizx, sizy) | Allocates and zero-fills sizx * sizy bytes |
| A(38h) | realloc(old_buf, new_size) | Changes the size of a block |
| A(39h) | InitHeap(addr, size) | Sets the heap address and size and releases all blocks19 |
rand() advances the seed as x = x * 0x41C64E6D + 0x3039 and returns (x / 0x10000) AND 0x7FFF.14 The ROM malloc() has a bug in which free() cannot release an area completely. Because the ROM cannot be corrected, Sony added malloc2() in RAM and the faster malloc3() in Library 4.0.20
Console Functions
These functions use the TTY device (standard input fd 0 and standard output fd 1).21
| Number | Function | Explanation |
|---|---|---|
| A(3Ah) | _exit(exitcode) | Stops the system |
| A(3Bh) | getchar() | Reads one character, masked to 7 bits |
| A(3Ch) | putchar(char) | Writes one character (TAB and LF expanded) |
| A(3Dh) | gets(dst) | Reads a line into a 128-byte buffer with echo |
| A(3Eh) | puts(src) | Writes a string |
| A(3Fh) | printf(txt, ...) | Writes a formatted string (%c %s %d %u %o %x %n) |
Executable Functions
These functions load and start PS-X EXE files. They are described on the boot page.22
| Number | Function | Explanation |
|---|---|---|
| A(40h) | SystemErrorUnresolvedException() | Stops the system after an unhandled exception |
| A(41h) | LoadTest(filename, headerbuf) | Reads the execution file information of a file23 |
| A(42h) | Load(filename, headerbuf) | Loads an execution file and flushes the I-cache24 |
| A(43h) | Exec(headerbuf, param1, param2) | Executes a loaded module25 |
| A(44h) | FlushCache() | Flushes the instruction cache26 |
| A(45h) | init_a0_b0_c0_vectors() | Copies the three function vectors to 0xA0 to 0xCF |
| A(51h) | LoadExec(filename, stackbase, stackoffset) | Loads and executes a file, then restarts the boot file27 |
| A(52h) | GetSysSp() | Returns the top of the system stack28 |
| A(9Ch) | SetConf(num_EvCB, num_TCB, stacktop) | Changes the kernel configuration29 |
| A(9Dh) | GetConf(num_EvCB_dst, num_TCB_dst, stacktop_dst) | Reads the kernel configuration30 |
| A(9Fh) | SetMem(megabytes) | Sets the valid memory size to 2 or 8 MB31 |
| A(A0h) | _boot() | Reboots the system from CD-ROM32 |
| A(A1h) | SystemError(type, errorcode) | Stops the system with an error type ("B" boot, "D" disk)33 |
Sony describes SystemError() as a function that displays a system error screen and calls exit() on the PlayStation.33 psx-spx finds that the retail BIOS function jumps to itself and hangs the PlayStation.34
GPU Functions
These functions write the GPU ports at 0x1F801810 (GP0) and 0x1F801814 (GP1) directly.35
| Number | Function | Explanation |
|---|---|---|
| A(46h) | GPU_dw(Xdst, Ydst, Xsiz, Ysiz, src) | Transfers an image to VRAM by software |
| A(47h) | gpu_send_dma(Xdst, Ydst, Xsiz, Ysiz, src) | Transfers an image to VRAM by DMA |
| A(48h) | SendGP1Command(gp1cmd) | Writes a GP1 command |
| A(49h) | GPU_cw(gp0cmd) | Waits for the GPU, then writes one GP0 word |
| A(4Ah) | GPU_cwp(src, num) | Waits for the GPU, then writes num GP0 words |
| A(4Bh) | send_gpu_linked_list(src) | Starts a linked-list DMA of an ordering table |
| A(4Ch) | gpu_abort_dma() | Stops GPU DMA and issues GP1(04h), GP1(02h) and GP1(01h) |
| A(4Dh) | GetGPUStatus() | Returns GPUSTAT |
| A(4Eh) | gpu_sync() | Waits until the GPU is ready for a command |
GPU_dw() transfers Xsiz * Ysiz / 2 words. When Xsiz * Ysiz is odd, the last halfword is not sent and the GPU waits for it. In the same way gpu_send_dma() sends Xsiz * Ysiz / 32 blocks of 16 words, and the remainder is lost.35
CD-ROM Functions
These functions control the CD-ROM drive below the file system. They are described on the file I/O page.36
| Number | Function | Explanation |
|---|---|---|
| A(54h), A(71h) | _96_init() | Installs the ISO 9660 file system driver37 |
| A(56h), A(72h) | _96_remove() | Removes the ISO 9660 driver (does not work)38 |
| A(78h) | CdAsyncSeekL(src) | Issues Setloc and SeekL to an MM:SS:FF position |
| A(7Ch) | CdAsyncGetStatus(dst) | Issues GetStat |
| A(7Eh) | CdAsyncReadSector(count, dst, mode) | Issues SetMode and ReadN or ReadS |
| A(81h) | CdAsyncSetMode(mode) | Issues SetMode |
| A(90h) to A(93h) | CdromIoIrqFunc1() and others | Internal CD-ROM interrupt handlers |
| A(94h) | CdromGetInt5errCode(dst1, dst2) | Returns the status and error code of the last INT5 |
| A(95h) | CdInitSubFunc() | Subfunction of _96_init |
| A(96h) | AddCDROMDevice() | Installs the cdrom device |
| A(9Eh) | SetCdromIrqAutoAbort(type, flag) | Internal |
| A(A2h) | EnqueueCdIntr() | Installs the CD-ROM interrupt handlers with priority 0 |
| A(A3h) | DequeueCdIntr() | Removes them (does not work) |
| A(A4h) | CdGetLbn(filename) | Returns the first sector of a file |
| A(A5h) | CdReadSector(count, sector, buffer) | Reads 2048-byte sectors at double speed and waits |
| A(A6h) | CdGetStatus() | Returns the drive status byte |
_96_remove() and DequeueCdIntr() call SysDeqIntRP(), which can remove only the first element of a priority chain. They therefore fail to remove the CD-ROM handlers.3615
Memory Card Functions
These functions are the lower level of the Memory Card file system. They are described on the file I/O page.39
| Number | Function | Explanation |
|---|---|---|
| A(55h), A(70h) | _bu_init() | Initializes the Memory Card file system |
| A(97h) | AddMemCardDevice() | Installs the bu device |
| A(A7h) to A(AAh), A(AEh) | bufs_cb_0() to bufs_cb_4() | Internal completion callbacks |
| A(ABh) | _card_info(port) | Checks a card with a dummy read |
| A(ACh) | _card_load(port) | Reads the directory asynchronously |
| A(ADh) | _card_auto(flag) | Turns automatic formatting on (1) or off (0) |
| A(AFh) | card_write_test(port) | Clears the card change flag with a dummy write to sector 0x3F |
Device Functions
The kernel drivers for its three standard devices are A functions. They are called through the device control blocks and not by applications.40
| Number | Function |
|---|---|
| A(5Bh) to A(5Eh) | dev_tty_init, dev_tty_open, dev_tty_in_out, dev_tty_ioctl |
| A(5Fh) to A(64h) | dev_cd_open, dev_cd_read, dev_cd_close, dev_cd_firstfile, dev_cd_nextfile, dev_cd_chdir |
| A(65h) to A(6Eh) | dev_card_open, dev_card_read, dev_card_write, dev_card_close, dev_card_firstfile, dev_card_nextfile, dev_card_erase, dev_card_undelete, dev_card_format, dev_card_rename |
| A(6Fh) | Clears the error field of a card FCB |
| A(98h) | AddDuartTtyDevice() |
| A(99h) | add_nullcon_driver() |
Other Functions
| Number | Function | Explanation |
|---|---|---|
| A(B2h) | _ioabort_raw(param) | Executes longjmp to the I/O abort buffer |
| A(B4h) | GetSystemInfo(index) | Returns the kernel date (0), flags (1), version string (2) or RAM size in KB (5) |
Unused Numbers
Some numbers have no function. A(57h) to A(5Ah), A(73h) to A(77h), A(79h) to A(7Bh), A(7Dh), A(7Fh), A(80h), A(82h) to A(8Fh), A(B0h), A(B1h) and A(B3h) return 0. A(4Fh), A(50h), A(53h), A(9Ah) and A(9Bh) are SystemError functions that loop forever. A(B5h) to A(BFh) jump to address 0.34 psx-spx also lists A(52h) among these SystemError functions, although the function summary of psx-spx gives A(52h) the name GetSysSp.341
References
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^ a b c d psx-spx. Kernel (BIOS), BIOS Function Summary, A-Functions. https://psx-spx.consoledev.net/kernelbios/
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^ Sony Computer Entertainment Inc. Run-Time Library Reference. January 1999. Page 1-63, SetMem.
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^ psx-spx. Kernel (BIOS), BIOS More Internal Functions. https://psx-spx.consoledev.net/kernelbios/