You can increase fontsize, try downloading a manual at rockbox.org for more info
~ $ dpkg -L rockbox|grep fnt /opt/rockbox/share/rockbox/fonts/14-Terminus-Bold.fnt /opt/rockbox/share/rockbox/fonts/13-Fixed-Bold.fnt /opt/rockbox/share/rockbox/fonts/13-Nimbus.fnt /opt/rockbox/share/rockbox/fonts/24-Terminus-Bold.fnt /opt/rockbox/share/rockbox/fonts/20-Terminus.fnt /opt/rockbox/share/rockbox/fonts/14-Rockbox-Mix.fnt /opt/rockbox/share/rockbox/fonts/10-Sazanami-Mincho.fnt /opt/rockbox/share/rockbox/fonts/28-Terminus-Bold.fnt /opt/rockbox/share/rockbox/fonts/27-Adobe-Helvetica.fnt /opt/rockbox/share/rockbox/fonts/35-Adobe-Helvetica-Bold.fnt /opt/rockbox/share/rockbox/fonts/07-Fixed.fnt /opt/rockbox/share/rockbox/fonts/18-Adobe-Helvetica-Bold.fnt /opt/rockbox/share/rockbox/fonts/08-Nedore.fnt /opt/rockbox/share/rockbox/fonts/08-Schumacher-Clean.fnt /opt/rockbox/share/rockbox/fonts/14-Terminus.fnt /opt/rockbox/share/rockbox/fonts/19-Nimbus.fnt /opt/rockbox/share/rockbox/fonts/13-Fixed-SemiCond-Bold.fnt /opt/rockbox/share/rockbox/fonts/13-Fixed.fnt /opt/rockbox/share/rockbox/fonts/08-Namil.fnt /opt/rockbox/share/rockbox/fonts/35-Nimbus.fnt /opt/rockbox/share/rockbox/fonts/20-Terminus-Bold.fnt /opt/rockbox/share/rockbox/fonts/12-Fixed-SemiCond.fnt /opt/rockbox/share/rockbox/fonts/10-Adobe-Helvetica-Bold.fnt /opt/rockbox/share/rockbox/fonts/10-Nimbus.fnt /opt/rockbox/share/rockbox/fonts/12-ProFont.fnt /opt/rockbox/share/rockbox/fonts/12-Sazanami-Mincho.fnt /opt/rockbox/share/rockbox/fonts/10-Adobe-Helvetica.fnt /opt/rockbox/share/rockbox/fonts/12-Terminus.fnt /opt/rockbox/share/rockbox/fonts/16-Adobe-Helvetica-Bold.fnt /opt/rockbox/share/rockbox/fonts/10-Fixed.fnt /opt/rockbox/share/rockbox/fonts/09-Sazanami-Mincho.fnt /opt/rockbox/share/rockbox/fonts/14-Nimbus.fnt /opt/rockbox/share/rockbox/fonts/10-ProFont.fnt /opt/rockbox/share/rockbox/fonts/15-Adobe-Helvetica.fnt /opt/rockbox/share/rockbox/fonts/32-Terminus-Bold.fnt /opt/rockbox/share/rockbox/fonts/14-Sazanami-Mincho.fnt /opt/rockbox/share/rockbox/fonts/11-ProFont.fnt /opt/rockbox/share/rockbox/fonts/16-GNU-Unifont.fnt /opt/rockbox/share/rockbox/fonts/08-Rockfont.fnt /opt/rockbox/share/rockbox/fonts/21-Adobe-Helvetica-Bold.fnt /opt/rockbox/share/rockbox/fonts/20-Artwiz-Snap.fnt /opt/rockbox/share/rockbox/fonts/08-Fixed.fnt /opt/rockbox/share/rockbox/fonts/08-Atadore.fnt /opt/rockbox/share/rockbox/fonts/16-Adobe-Helvetica.fnt /opt/rockbox/share/rockbox/fonts/15-ProFont.fnt /opt/rockbox/share/rockbox/fonts/12-Nimbus.fnt /opt/rockbox/share/rockbox/fonts/35-Adobe-Helvetica.fnt /opt/rockbox/share/rockbox/fonts/08-Sazanami-Mincho.fnt /opt/rockbox/share/rockbox/fonts/13-Sazanami-Mincho.fnt /opt/rockbox/share/rockbox/fonts/06-Tiny.fnt /opt/rockbox/share/rockbox/fonts/05-Tiny.fnt /opt/rockbox/share/rockbox/fonts/09-Nedore.fnt /opt/rockbox/share/rockbox/fonts/10-Artwiz-Snap.fnt /opt/rockbox/share/rockbox/fonts/18-Fixed.fnt /opt/rockbox/share/rockbox/fonts/16-Terminus.fnt /opt/rockbox/share/rockbox/fonts/29-ProFont.fnt /opt/rockbox/share/rockbox/fonts/13-Fixed-SemiCond.fnt /opt/rockbox/share/rockbox/fonts/28-Terminus.fnt /opt/rockbox/share/rockbox/fonts/09-Fixed.fnt /opt/rockbox/share/rockbox/fonts/32-Terminus.fnt /opt/rockbox/share/rockbox/fonts/11-Sazanami-Mincho.fnt /opt/rockbox/share/rockbox/fonts/22-ProFont.fnt /opt/rockbox/share/rockbox/fonts/24-Terminus.fnt /opt/rockbox/share/rockbox/fonts/14-Adobe-Helvetica-Bold.fnt /opt/rockbox/share/rockbox/fonts/12-Adobe-Helvetica-Bold.fnt /opt/rockbox/share/rockbox/fonts/11-Nimbus.fnt /opt/rockbox/share/rockbox/fonts/18-Fixed-Bold.fnt /opt/rockbox/share/rockbox/fonts/12-Adobe-Helvetica.fnt /opt/rockbox/share/rockbox/fonts/08-Rockbox-Propfont.fnt /opt/rockbox/share/rockbox/fonts/27-Adobe-Helvetica-Bold.fnt /opt/rockbox/share/rockbox/fonts/17-ProFont.fnt /opt/rockbox/share/rockbox/fonts/18-Adobe-Helvetica.fnt /opt/rockbox/share/rockbox/fonts/16-Jackash.fnt /opt/rockbox/share/rockbox/fonts/16-Terminus-Bold.fnt /opt/rockbox/share/rockbox/fonts/21-Adobe-Helvetica.fnt