; ***************************************************************************
; Determine which model of ZX Spectrum the code is running on.
;
; Author: Peter Mount, Area51.dev & Contributors
; URL: https://area51.dev/sinclair/asm/machinetype/
; ***************************************************************************

; The model's to detect
machine_48      = 0                 ; Spectrum 48k
machine_128     = 1                 ; Spectrum 128K UK
machine_128es   = 2                 ; Spectrum 128K Spanish
machine_plus2   = 3                 ; Spectrum +2
machine_plus3   = 4                 ; Spectrum +2A/+3

;
; detectMachine         Detect the type of machine running this code
;
; Exit:
;   A       Model type
;   Z       Set for a 16K/48K machine, Reset for any 128K machine
;
detectMachine:
            PUSH    BC                  ; Save registers as BC is needed for ROM selection
            PUSH    DE                  ; and D for passing the result back
            CALL    detectMachine1      ; Call detection routine
            LD      A, D                ; Copy result into A
            POP     DE                  ; Restore registers
            POP     BC
            AND     A                   ; CP 0 so Z is true for a 48K and NZ for any 128K machine
            RET

detectMachine1:
            LD      A, (0x5B5C)         ; Switch rom
            PUSH    AF                  ; Save current rom
            AND     &EF                 ; to ensure non-48k rom is selected, bit 4 is 0
            CALL    romSel1             ; change rom1, will do nothing on a 48K
            CALL    detectMachine2      ; run tests
            POP     AF                  ; Restore rom

; romSel1   Update rom selection port on 128K and later machines
;
; Entry:
;   A       New value of port, based on current value in 0x5BFC
;
; Exit:
;   A       undefined
;   BC      undefined
;
romSel1:    LD      BC, 0x7FFD          ; Select rom on 128K and later
            DI                          ; Switch the port between DI/EI
            LD      (0x5B5C), A
            OUT     (C), A
            EI
            RET

detectMachine2:
            LD      D, machine_48       ; Test for a 48K
            LD      A, (0x153B)         ; Address of 1 in (C)1982 in spectrum 48k rom
            CP      '1'
            RET     Z

            LD      A, (0x5B67)         ; Switch rom on +3
            PUSH    AF                  ; Save current rom
            AND     &FB                 ; This time bit 2 is 0 on second port, does nothing on 128/+2
            CALL    romSel2
            CALL    detectMachine3      ; run tests
            POP     AF                  ; restoring old rom

; romSel2   Update rom selection port on +2A and +3 machines
;
; Entry:
;   A       New value of port, based on current value in 0x5B67
;
; Exit:
;   A       undefined
;   BC      undefined
;
romSel2:    LD      BC, 0x1FFD          ; Select rom on +2A/+3
            DI                          ; Switch the port between DI/EI
            LD      (0x5B67), A
            OUT     (C), A
            EI
            RET

detectMachine3:
            LD      D, machine_plus3    ; Test for +3
            LD      A, (0x168e)         ; Address of "SPECTRUM" in +3 rom 0
            CP      'S'
            RET     Z

            LD      D, machine_plus2    ; Test for +2
            LD      A, (0x0562)         ; See if we are a +2
            CP      '1'                 ; This is 1 in "(C)1982 Amstrad"
            RET     Z

            LD      D, machine_128es    ; See if Spanish 128K
            LD      A, (0x0508)
            CP      '1'                 ; This is 1 in "(C) 1985 Sinclair"
            RET     Z

            LD      D, machine_128      ; We must be a 128K if we got here
            RET