__ ;* ======================================================================== *; ;* This file is hereby placed into the public domain by its author, *; ;* Joseph Zbiciak. It may therefore be incorporated into programs *; ;* with any license with no restrictions on the resulting program. *; ;* ======================================================================== *; _ ;; ======================================================================== ;; ;; INITMEM ;; ;; ;; ;; Initialize a set of variables to initial values. Initialization ;; ;; records are 1 word each typically. All variables are in the range ;; ;; $0F0 - $35F. So, each record is formatted as follows. ;; ;; ;; ;; 15 10 9 0 ;; ;; +---------------------+-----------------------------------+ ;; ;; | Value | Address | ;; ;; +---------------------+-----------------------------------+ ;; ;; ;; ;; A record of 0 terminates the initializer list. ;; ;; ;; ;; The "value" field is actually encoded. $20 - $3F directly map to ;; ;; the constants $00 - $1F. $00 - $1E map to constants in a separate ;; ;; constants table. $1F indicates the constant appears in the following ;; ;; word. Furthermore, constant table entries $00 - $1F are packed 8-bit ;; ;; contants, whereas $20 - $2E are unpacked 16-bit constants. ;; ;; ;; ;; INPUTS (INITMEM.0) ;; ;; R5 Initializer table. Returns following table. ;; ;; ;; ;; INPUTS (INITMEM.1) ;; ;; R5 Pointer to initializer table. Returns following pointer. ;; ;; ;; ;; INPUTS (INITMEM.2) ;; ;; R5 Return address ;; ;; R4 Initialization table ;; ;; ;; ;; ======================================================================== ;; INITMEM PROC @@0: MOVR R5, R4 ; Read init table from after CALL CLRR R5 ; Flag: Return to R4. INCR PC ; Skip MVI@ @@1: MVI@ R5, R4 ; Read init table from elsewhere @@2: @@next: ;; ------------------------------------------------------------ ;; ;; Decode next initializer symbol. R1 will hold the 10-bit ;; ;; variable address and R2 holds the encoded constant value. ;; ;; ------------------------------------------------------------ ;; MVI@ R4, R2 ; Get next record MOVR R2, R1 ; Save for factoring addr from cst BEQ @@done ; Terminate on zero ANDI #$3FF, R1 ; Factor address from data XORR R1, R2 ; Clear address from data SWAP R2 ; \_ put data in 6 LSBs SLR R2, 2 ; / SUBI #$20, R2 ; $20-$3F are cst $00-$1F. BMI @@cst_tbl ; $00-$1F indicate "constant tbl" MVO@ R2, R1 ; \_ Store decoded constant B @@next ; / and move to next initializer ;; ------------------------------------------------------------ ;; ;; If the encoded value was $00 - $1F, then we have one of ;; ;; the following: ;; ;; $00 - $0F 8 bit constant in packed 8-bit table ;; ;; $10 - $1E 16 bit constant in 16-bit table ;; ;; $1F Escape code for arbitrary constant. ;; ;; ------------------------------------------------------------ ;; @@cst_tbl INCR R2 ; \_ $1F specifies an escape BEQ @@escape ; / ADDI #$F, R2 ; \_ $00-$0F specify 8 bit cst BMI @@8bit ; / $10-$1E specify 16 bit cst ;; ------------------------------------------------------------ ;; ;; R2 now $00-$0E for $10-$1E input. Use it to index into ;; ;; 16-bit constants table. ;; ;; ------------------------------------------------------------ ;; ADDI #CST16, R2 MVI@ R2, R0 ; \_ Copy constant of interest out MVO@ R0, R1 ; / B @@next @@escape MVI@ R4, R2 ; \_ Escape: Copy next word to MVO@ R2, R1 ; / indicated address B @@next @@8bit: ;; ------------------------------------------------------------ ;; ;; R2 is now -$10 to -$01 to specify one of the 16 8-bit csts. ;; ;; We add CST8*2 to the index and then right-shift by 1 to ;; ;; determine the integer index. The C bit will tell us hi or ;; ;; lo byte. We bias the result up by $20 since $00-$1F don't ;; ;; require the constant table. ;; ;; ------------------------------------------------------------ ;; ADDI #$FFFF AND (CST8*2+16), R2 ; IF (DEFINED CST8) AND ((CST8 AND $8000) = 0) CLRC ; MSB of CST8 was 0 ELSE _cst8_fix SETC ; MSB of CST8 was 1 ENDI RRC R2 ; Divide index by 2 MVI@ R2, R0 ; Get pair of 8 bit values ADCR PC ; If idx%2 == 1, take lo half SWAP R0 ; else take hi half ANDI #$FF, R0 ; Clear away upper byte ADDI #$20, R0 ; MVO@ R0, R1 ; Store it out B @@next @@done TSTR R5 ; Return after data? BEQ @@jrr4 ; If R5==0, return after data. JR R5 ; Else return to R5. @@jrr4 JR R4 ENDP