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⌂ ∞ ▽ Elite on the BBC Micro and NES

Market: TT219

[Elite-A, Parasite]

       Name: TT219                                                   [Show more]
       Type: Subroutine
   Category: Market
    Summary: Show the Buy Cargo screen (red key f1) or Special Cargo screen
             (CTRL-f1)

    Context: See this subroutine in context in the source code
 References: This subroutine is called as follows:
             * TT102 calls TT219
             * gnum calls via BAY2
             * TT210 calls via BAY2




 Other entry points:

   BAY2                 Jump into the main loop at FRCE, setting the key
                        "pressed" to red key f9 (so we show the Inventory
                        screen)



.TT219

 LDA #2                 \ Clear the top part of the screen, draw a white border,
 JSR TT66               \ and set the current view type in QQ11 to 2

 JSR CTRL               \ Scan the keyboard to see if CTRL is currently pressed,
                        \ returning a negative value in A if it is

 BPL buy_ctrl           \ If CTRL is not being pressed, jump to buy_ctrl to skip
                        \ the next instruction

 JMP cour_buy           \ CTRL-f1 is being pressed, so jump to cour_buy to show
                        \ the Special Cargo screen, returning from the
                        \ subroutine using a tail call
.buy_ctrl

 JSR TT163              \ Print the column headers for the prices table

 LDA #%10000000         \ Set bit 7 of QQ17 to switch to Sentence Case, with the
 STA QQ17               \ next letter in capitals

 JSR FLKB               \ Flush the keyboard buffer

 LDA #0                 \ We're going to loop through all the available market
 STA QQ29               \ items, so we set up a counter in QQ29 to denote the
                        \ current item and start it at 0

.TT220

 JSR TT151              \ Call TT151 to print the item name, market price and
                        \ availability of the current item, and set QQ24 to the
                        \ item's price / 4, QQ25 to the quantity available and
                        \ QQ19+1 to byte #1 from the market prices table for
                        \ this item

 LDA QQ25               \ If there are some of the current item available, jump
 BNE TT224              \ to TT224 below to see if we want to buy any

 JMP TT222              \ Otherwise there are none available, so jump down to
                        \ TT222 to skip this item

.TQ4

 LDY #176               \ Set Y to the recursive token 16 ("QUANTITY")

.Tc

 JSR TT162              \ Print a space

 TYA                    \ Print the recursive token in Y followed by a question
 JSR prq                \ mark

.TTX224

 JSR dn2                \ Call dn2 to make a short, high beep and delay for 1
                        \ second

.TT224

 JSR CLYNS              \ Clear the bottom three text rows of the upper screen,
                        \ and move the text cursor to column 1 on row 21, i.e.
                        \ the start of the top row of the three bottom rows

 LDA #204               \ Print recursive token 44 ("QUANTITY OF ")
 JSR TT27

 LDA QQ29               \ Print recursive token 48 + QQ29, which will be in the
 CLC                    \ range 48 ("FOOD") to 64 ("ALIEN ITEMS"), so this
 ADC #208               \ prints the current item's name
 JSR TT27

 LDA #'/'               \ Print "/"
 JSR TT27

 JSR TT152              \ Print the unit ("t", "kg" or "g") for the current item
                        \ (as the call to TT151 above set QQ19+1 with the
                        \ appropriate value)

 LDA #'?'               \ Print "?"
 JSR TT27

 JSR TT67               \ Print a newline

 JSR gnum               \ Call gnum to get a number from the keyboard, which
                        \ will be the quantity of this item we want to purchase,
                        \ returning the number entered in A and R

 BCS TQ4                \ If gnum set the C flag, the number entered is greater
                        \ than the quantity available, so jump up to TQ4 to
                        \ display a "Quantity?" error, beep, clear the number
                        \ and try again

 STA P                  \ Otherwise we have a valid purchase quantity entered,
                        \ so store the amount we want to purchase in P

 JSR tnpr               \ Call tnpr to work out whether there is room in the
                        \ cargo hold for this item

 LDY #206               \ Set Y to recursive token 46 (" CARGO{sentence case}")
                        \ to pass to the Tc routine if we call it

 BCS Tc                 \ If the C flag is set, then there is no room in the
                        \ cargo hold, jump up to Tc to print a "Cargo?" error,
                        \ beep, clear the number and try again

 LDA QQ24               \ There is room in the cargo hold, so now to check
 STA Q                  \ whether we have enough cash, so fetch the item's
                        \ price / 4, which was returned in QQ24 by the call
                        \ to TT151 above and store it in Q

 JSR GCASH              \ Call GCASH to calculate:
                        \
                        \   (Y X) = P * Q * 4
                        \
                        \ which will be the total price of this transaction
                        \ (as P contains the purchase quantity and Q contains
                        \ the item's price / 4)

 JSR LCASH              \ Subtract (Y X) cash from the cash pot in CASH

 LDY #197               \ If the C flag is clear, we didn't have enough cash,
 BCC Tc                 \ so set Y to the recursive token 37 ("CASH") and jump
                        \ up to Tc to print a "Cash?" error, beep, clear the
                        \ number and try again

 LDY QQ29               \ Fetch the current market item number from QQ29 into Y

 LDA R                  \ Set A to the number of items we just purchased (this
                        \ was set by gnum above)

 PHA                    \ Store the quantity just purchased on the stack

 CLC                    \ Add the number purchased to the Y-th byte of QQ20,
 ADC QQ20,Y             \ which contains the number of items of this type in
 STA QQ20,Y             \ our hold (so this transfers the bought items into our
                        \ cargo hold)

 LDA AVL,Y              \ Subtract the number of items from the Y-th byte of
 SEC                    \ AVL, which contains the number of items of this type
 SBC R                  \ that are available on the market
 STA AVL,Y

 PLA                    \ Restore the quantity just purchased

 BEQ TT222              \ If we didn't buy anything, jump to TT222 to skip the
                        \ following instruction

 JSR dn                 \ Call dn to print the amount of cash left in the cash
                        \ pot, then make a short, high beep to confirm the
                        \ purchase, and delay for 1 second

.TT222

 LDA QQ29               \ Move the text cursor to row QQ29 + 5 (where QQ29 is
 CLC                    \ the item number, starting from 0)
 ADC #5
 STA YC

 LDA #0                 \ Move the text cursor to column 0
 STA XC

 INC QQ29               \ Increment QQ29 to point to the next item

 LDA QQ29               \ If QQ29 >= 17 then jump to BAY2 as we have done the
 CMP #17                \ last item
 BCS BAY2

 JMP TT220              \ Otherwise loop back to TT220 to print the next market
                        \ item

.BAY2

 LDA #f9                \ Jump into the main loop at FRCE, setting the key
 JMP FRCE               \ "pressed" to red key f9 (so we show the Inventory
                        \ screen)