Synopsis #

Header: fxcg/display.h
Syscall index: 0x01A2
Function signature: void Bdisp_DDRegisterSelect(int registerno)

Probably responsible for setting a register on the LCD controller (0xB4000000).

Comments #

This syscall clears bit 4 of 0xA405013C.b, writes registerno (r4) to 0xB4000000 and finally sets bit 4 of 0xA405013C.b again. It looks as if bit 4 controls the LCD-driver’s RS-bit; refer to the R61509-manual for more information.

After every write to 0xA405013C or 0xB4000000, the SH-4A processor instruction SYNCO is performed. You can see this in action by reading the disassembly.


var_2       = -2

        add #-4, r15
        mov.l   #0xA405013C, r3
        mov #~16, r5
        mov r4, r0
        mov.w   r0, @(4+var_2,r15)
        mov.b   @r3, r1     ! Read a byte from the address 0xA405013C and store that byte into R1
        and r5, r1      ! Clear bit four of R1
        mov.b   r1, @r3
        mov #0xFFFFFFB4, r6
        shll8   r6
        shll16  r6      ! R6 = 0xB4000000
        mov.w   r4, @r6
        mov.b   @r3, r0
        or  #16, r0
        mov.b   r0, @r3
        add #4, r15
! End of function Bdisp_DDRegisterSelect